Corrosion Engineering Pune University MCQs
Corrosion Engineering Pune University MCQs
This set of Corrosion Engineering Multiple Choice Questions & Answers focuses on “Corrosion and its Classification – 1”.
1. What is Corrosion?
a) Destruction or deterioration of a material
b) Conversion of metal atoms to metallic ions
c) Conversion of metal ions to metal atoms
d) Destruction of materials involving in the conversion of metal atoms into metal ions
Answer: d
Explanation: Corrosion is a destructive or deterioration of a material because of reaction with its environment. It occurs due to the higher stability of metal ions than the metal atoms.
2. Corrosion of metals is considered as the reverse of extractive metallurgy.
a) True
b) False
Answer: a
Explanation: Extractive metallurgy is a process of conversion of metal ions from the compounded state to metal atoms in the elemental state, whereas the corrosion occurs by the conversion of metal atoms into metal ions.
3. The chemical formula of rust is ______
a) Fe 1 O
b) Fe 2 O 3
c) Fe 3 O 4
d) Fe 2
Answer: b
Explanation: Corrosion of Iron is generally known as rusting. The chemical reaction can be represented as 4Fe + 3O 2 ==> 2Fe 2 O 3 .
4. Which of the following materials will undergo Corrosion?
a) Metals only
b) Metals and Non-metals
c) Metals, Non-metals, Ceramics and Plastics
d) Metals, Non-metals, Ceramics, Plastics and Rubbers
Answer: d
Explanation: Corrosion is defined as the destruction or deterioration of a material because of reaction with its environment. Every material in the universe will undergo corrosion but it varies in time and form. Any Physical, Chemical or Mechanical deviation of the original material is known as Corrosion.
5. Corrosion of material by furnace gases is classified as _____
a) wet corrosion
b) dry corrosion
c) galvanic corrosion
d) crevice corrosion
Answer: b
Explanation: Dry corrosion occurs in the absence of moisture usually by vapors and gases whereas the wet corrosion, galvanic corrosion and crevice corrosion occurs in aqueous state or in the presence of moisture.
6. Which of the following is an example of wet corrosion?
a) Corrosion of metal in the water
b) Corrosion of iron in the presence of anhydrous calcium chloride
c) Corrosion of titanium in dry chlorine
d) Corrosion due to furnace gases
Answer: a
Explanation: Wet corrosion occurs when the liquid is present. This usually involves aqueous solutions or electrolytes as corrosive mediums. Corrosion of iron in the presence anhydrous calcium chloride, by furnace gases and by dry chlorine are classified under dry corrosion.
7. Corrosion maintenance is vital in _____ industries.
a) paper
b) petroleum
c) plastic toy
d) both petroleum and paper
Answer: d
Explanation: The operating conditions in both the petroleum and paper industry are mainly in aqueous state with various chemicals in it. Hence these are likely prone to various electrochemical reactions which causes corrosion. Maintenance works include periodic inspection and replacements of partially corroded parts. It minimizes costly catastrophic failures, unscheduled down time, resulting in increased production and revenue.
8. Which of the following subjects are important in understanding and controlling corrosion?
a) Thermodynamics
b) Electrochemistry
c) Both Thermodynamics and Electrochemistry
d) Material Characterization
Answer: c
Explanation: Thermodynamic studies and calculations indicate the spontaneous direction of the reaction. The thermodynamic stability of corrosion product is relatively higher than reactant. Whereas the electrochemistry deals with electrode kinetics of the reaction.
9. Deterioration of paint and rubber by sunlight or chemicals is not a corrosion.
a) True
b) False
Answer: b
Explanation: Any deviation in the physical, chemical and mechanical properties of a material is considered as corrosion. Here we can notice physical change so it is a corrosion.
10. Which of the following is an incorrect statement?
a) Corrosion is an irreversible process
b) Corrosion is a non-spontaneous process
c) Corrosion is a degradation process
d) Corrosion is a spontaneous process
Answer: b
Explanation: Corrosion is a spontaneous process which results in degradation of materials and it is irreversible in nature. Spontaneous reaction is a reaction which results in the formation of stable products from unstable without need of any external energy.
11. Which of the following is considered as high corrosive resistant material?
a) Mild steel
b) Cast iron
c) Zinc
d) Stainless steel
Answer: d
Explanation: Corrosion resistant material is the material which has less corrosion rate in a particular atmosphere without much degradation. Stainless steel is considered as corrosion resistant material. This is because it forms chromic oxide layer over its surface to avoid physical contact with the outside environment.
12. Corrosion involves _______ reactions.
a) oxidation
b) reduction
c) displacement
d) both oxidation and reduction
Answer: d
Explanation: Corrosion is an electrochemical reaction. It occurs by therelease and gain of electrons from various species which are termed as oxidation and reduction respectively. It can be observed with change in the oxidation state of the species.
13. Which of the following are necessary in the process of corrosion?
a) Anode
b) Cathode
c) Electrolyte
d) Anode, Cathode and Electrolyte
Answer: d
Explanation: Corrosion occurs by the creation of electrochemical cell which includes a cathode, an anode and an electrolyte. A high reduction potential will act as cathode and other will acts as anode preferentially and electrolyte is needed to transfer ions between these two electrodes.
14. What is the reason for corrosion?
a) Stability of a metal ion
b) Stability of a metal atom
c) Passivation
d) Use of coatings
Answer: a
Explanation: Negative or less Gibbs free energy of the metal ions is the reason for corrosion whereas passivation and use of coatings decreases the extent of corrosion.
15. What are the advantages of corrosion?
a) Protection of metals by surficial oxide layer
b) Zn-carbon electrochemical reactions in the battery
c) Decrease in the strength of material
d) Protection of metals by the surficial oxide layer and Zn-carbon electrochemical reactions in the battery
Answer: d
Explanation: Initially passivating metals undergoes corrosion in order to form oxide layer. These thick, dense oxide layer acts as a strong barrier and protects the inner metal against corrosion. The Zn-carbon batteries works on the principle of galvanic corrosion. It involves conversion of chemical energy into electrical energy by these electrochemical reactions.
This set of Corrosion Engineering Interview Questions and Answers focuses on “Corrosion and its Classification – 2”.
1. Which of the following factors affect the corrosion rate of metal?
a) Relative surface area of an anode and cathode
b) Nature of the oxide layer
c) Purity of metal
d) Relative surface area of an anode and cathode, nature of oxide layer and purity of metal
Answer: d
Explanation: As the cathodic to anodic area increases, the more oxygen reduction, or more corrosion can occur. The corrosion resistance of aluminum can be attributed to the formation of the thick, dense oxide layer. Impure metals undergo corrosion at a faster rate than the pure metals.
2. The cathodic reaction that occurs during corrosion in oxygenated acidic solution is ______
a) 2H + +2e – ==>H 2
b) 4H + +O 2 +4e – ==>2H 2 O
c) 2H 2 O+2e – ==>H 2 +2OH –
d) 2H 2 O+O 2 +4e – ==>4OH –
Answer: b
Explanation: The common hydrogen reduction reaction in corrosion will proceed based on the pH and the amount of oxygen present in the solution. Then oxygenated acidic solution will react as
4H + +O 2 +4e – ==>2H 2 O.
3. If a metal undergoes uniform corrosion it becomes _____
a) thinner
b) thicker
c) perforated
d) thicker and perforated
Answer: a
Explanation: Uniform corrosion is the most common form of corrosion. It is characterized by an electrochemical reaction that proceeds uniformly over the entire exposed surface. Thus, the metal becomes thinner.
4. Which theory explains the oxidation of metals?
a) Collison theory
b) Molecular orbital theory
c) Wagner’s theory
d) Mixed potential theory
Answer: c
Explanation: Wagner’s theory states that the oxidation of metal is electrolytic in nature and the rate of oxidation is determined by the electrical properties of the corrosion product.
5. What is the mechanism of dry corrosion?
a) Absorption
b) Electrochemical
c) Differential solubility
d) Both electrochemical and differential solubility
Answer: a
Explanation: Dry corrosion occurs in the absence of a liquid phase. Vapors and gases are usually the corrodents. These will hit and adsorbed on the metal surface to form corrosion. So dry corrosion can be explained by an absorption mechanism.
6. Which of the following corrosion contaminant will act as a protective layer?
a) AgCl
b) SnCl 2
c) Fe 2 O 3
d) CaO
Answer: a
Explanation: Silver on reaction with chlorine forms silver chloride. It acts as a protective layer and prevents chlorine to corrode further. Here SnCl 2 and CaO are volatile in nature whereas Fe 2 O 3 is porous in nature. Hence, they can’t act as protective layers.
7. Corrosion of iron takes place even in the solid ice.
a) True
b) False
Answer: b
Explanation: Though ice is the solid form of water but it doesn’t conduct electrons. The function of an electrolyte is to transfers ions from one electrode to another. Thus, given statement is false. Corrosion needs an anode, a cathode and a conductive electrolyte.
8. What are the factors that affect corrosion?
a) Temperature
b) Humidity
c) Conductance of the corroding medium
d) Temperature, humidity and conductance of the corroding medium
Answer: d
Explanation: The main factors that affect the rate of corrosion includes the effect of pH, temperature, humidity, conductance of the corroding medium, oxygen concentration, presence of impurities. These factors are based on the nature of environment.
9. _______ is a chemical substance which reduces the corrosion rate.
a) Corrosion inhibitor
b) Corrosion initiator
c) Electrolyte
d) Corrosive medium
Answer: a
Explanation: An inhibitor is a substance that, when added in small concentrations to an environment, decreases the corrosion rate.
Following are the types of inhibitors:
i. Adsorption-type
ii. Hydrogen-evolution poisons
iii. Scavengers
iv. Vapor-phase
10. In the given figure, what does point A denote?
a) Cathodic spot
b) Anodic spot
c) Electrolyte
d) Oxide layer
Answer: a
Explanation: Cathodic spot, a place on the metal surface where the reduction reaction takes place. Reduction is a process in which atoms of the chemical reaction accepts electrons in order to form anion.
11. In the given figure, what does point B denote?
a) Cathodic spot
b) Anodic spot
c) Electrolyte
d) Oxide layer
Answer: b
Explanation: Anodic spot, a place on the metal surface where the oxidation reaction takes places. Oxidation is a loss of electrons or increase in the oxidation state during a reaction by a molecule or atom. Molecules or atoms on oxidation forms cations. Ex: Fe ==> Fe +2 + 2e – .
12. In the given figure, what does point C denote?
a) Cathodic spot
b) Anodic spot
c) Electrolyte
d) Oxide layer
Answer: c
Explanation: Electrolyte is a conductive medium between anode and cathode. It undergoes ionization when dissolved in water or ionizing solvents. The function of an electrolyte is to transfers ions from one electrode to another.
This set of Corrosion Engineering Multiple Choice Questions & Answers focuses on “Corrosion Damage”.
1. Which of the following are the destructive effects of corrosion?
a) Contamination of product
b) Effect on safety
c) Reliability
d) Contamination of product, effect on safety and reliability
Answer: d
Explanation: The market value of the product depends on purity and quality. Contamination of product decreases the market value of the product. Safety and reliability are the major concerns due to the catastrophic nature of corrosion. Economizing on materials of construction is not desirable if safety is risked.
2. Preventive action on corrosion is necessary and economical.
a) True
b) False
Answer: a
Explanation: Preventive action involves the replacement of partially corroded or failed equipment. It avoids plant shutdowns and contamination of a product. Hence, the process become more economical.
3. Which of the following corrosion damage is more emphasized in the construction material of restaurants?
a) Loss of appearance
b) Maintenance and operating cost
c) Effect of safety
d) Both loss of appearance and effect of safety
Answer: d
Explanation: Restaurants and in many other public places, the main concern about the corrosion is that the loss of appearance and effect of safety. Badly corroded and rusted products would leave a poor impression on the observer.
4. Etchants react with metallic surface and get corroded in order to use for the metallurgical investigation.
a) True
b) False
Answer: a
Explanation: We can’t differentiate grain and grain boundaries in a non-etched polished sample. Etchant is used to react with the grain boundaries in order to reveal grain and grain boundaries.
5. Main form of ceramic degradation is _________
a) dissolution
b) swelling
c) weathering
d) dissolution and swelling
Answer: c
Explanation: Weathering is the main form of degradation of ceramics. Weathering involves breakdown of ceramics through contact with the earth’s atmosphere, water, and biological organisms.
6. Which of the following are included in maintenance and operating costs?
a) Use of corrosion-resistant material
b) Loss of product
c) Regular inspections
d) Use of corrosion-resistant material and regular inspection
Answer: d
Explanation: Maintenance and operating costs are the preventive measures in order to avoid the plant shutdowns and catastrophic accidents. Plant shutdowns usually cost 5-10 times more than the maintenance and operating costs.
7. The effect of acid rains on Taj Mahal is also a corrosion.
a) True
b) False
Answer: a
Explanation: Oxides of carbon, Sulphur and nitrogen on reacting with rain water, forms dilute acids. These acids on reaction with the marble of Taj mahal degrades its appearance, hence it is regarded as corrosion. Acid rains also accelerates the natural corrosion and erosion.
8. Portable water pipelines of lead are replaced by various types of steels, due to _____
a) cheaper cost
b) more availability
c) contamination caused by lead
d) shiny appearance
Answer: c
Explanation: Lead exposure is a public health hazard as it causes development effects in infants and young children. Lead contamination in drinking water is the most contributor of lead exposure to humans. To avoid exposure, various steels such chromium steels and coated steels are being used for this purpose.
9. Which of the following tragediesthat occurred due to corrosion?
a) Bhopal tragedy
b) Crude oil leak in Canada
c) Both Bhopal tragedy and crude oil leak in Canada
d) Fukushima
Answer: c
Explanation: Bhopal gas tragedy is caused by the immediate flow of water into Methyl isocyanate gas tank. This resulted in the formation of much carbon dioxide and the temperature inside the tank reach over 200°C. Crude oil leakage in Canada occurred in 2017, occurred due to corrosion at the sealing.
10. Thermal gradients across the metal wall causes Stress cracking corrosion.
a) True
b) False
Answer: a
Explanation: Thermal gradients across the metal wall induces higher stresses in the metal. Internal stresses in the corrosive environments is the reason for the stress corrosion cracking.
This set of Advanced Corrosion Engineering Questions and Answers focuses on “Corrosion Rate Expression”.
1. What is meant by MPY in corrosion?
a) Mils penetration per year
b) Meter penetration per year
c) Milli meter penetration per year
d) Micro meter penetration per year
Answer: a
Explanation: MPY in corrosion is abbreviated as Mils penetration per year . It is usually used in the U.S. measurement system in order to estimate the corrosion rate of pitting corrosion.
2. Which of the following expression is used to calculate MPY?
a) MPY=/DAT
b) MPY=/DAT
c) MPY=W/DAT
d) MPY=DAT/
Answer: b
Explanation: W = weight loss in milligrams, D=Density of a specimen (g/cm 3 ), A=Area of specimen, T=time of exposure in hours and 534 is a conversion factor. MPY means mils penetration per year I.e. milli inches penetration per year.
3. MDD in corrosion is abbreviated as ______
a) milligrams/sq. decimeter/decade
b) millimeters/sq. decimeter/day
c) milligrams/sq. decimeter/day
d) microns/decimeter/decade
Answer: c
Explanation: MDD in corrosion known as milligrams/sq.decimeter/day. It is the common unit to measure weight loss of metal per unit area. It is usually used for uniform and galvanic corrosion.
4. MPY is used to measure weight loss per unit area.
a) True
b) False
Answer: b
Explanation: Usually mils per year is used to measure the penetration rate. Penetration is the average depth of metal loss in the specimen. MPY is usually used for pitting corrosion. MDD is used to measure the weight loss per unit area.
5. _____ is/are used to measure the extent of pitting corrosion.
a) MPY
b) MDD
c) Both MPY and MDD
d) MPK
Answer: a
Explanation: Pitting corrosion involves loss of metal at the selected spots on the surface of a metal. It penetrates into various depths based on the concentration of corrosive medium and nature of metal. MPY measures penetration range.
6. Which of the following law is used to derive the corrosion rate expression?
a) Newton’s law
b) Henry’s law
c) Raoult’s law
d) Faraday’s law
Answer: d
Explanation: Faraday’s law is used in order to derive the corrosion rate expression [W/At=I*a m /n*F]. W/At denotes the corrosion rate, I=current density, a m =molecular weight, n=number of electrons transferred, F=faraday constant .
7. Which following expression is used to find the corrosion rate from current density of a corroding specimen?
a) W/At = [(I × a m ) / ]
b) W/At = [(I × a m ) / ]
c) W/At = [534 × (I × a m ) / ]
d) W/At = [(I × a m ) / ] and W/At = [(I × a m ) / ]
Answer: d
Explanation: W/At denotes the corrosion rate, I= current density, am=molecular weight, n=number of electrons transferred, F=faraday constant , d=density of a specimen. [(I*a m ) / ] is used to calculate the MDD whereas the [(I*a m ) / ] is used to calculate the MPY.
8. Rate of oxidation is equals to the rate of reduction in corrosion.
a) True
b) False
Answer: a
Explanation: It is the second statement in the mixed potential theory that the number of electrons generated and consumed are same. Anode produces the same number of electrons that require for the cathode.
9. Iron is corroding at a current density of 1.69*10 -4 amp/cm 2 . What would be the corrosion rate in MDD?
a) 773
b) 723
c) 423
d) 473
Answer: c
Explanation: We know MDD = W/At = (I*a m ) / . We should convert the given unit values in milligrams/sq. Decimeter/day.
Given, I = 1.69*10 -4 amp/cm 2
Atomic weight of iron = a m = 55.86 g/mol
n = number of electrons = 2 [Fe ==> Fe +2 +2e – ]
F = faraday’s constant = 96500 coulombs
= (1.96×10 -4 coulombs /sec*cm 2 ) × ÷ (2×96500 coulombs )
= [(1.96×10 -4 )***(55.86 *10 3 )] / [2*96500]
= 422.53 MDD.
10. Iron is corroding at a current density of 1.69*10 -4 amp/cm 2 . What would be the corrosion rate in MPY?
a) 423
b) 77
c) 473
d) 97
Answer: b
Explanation: We know MDD = W/At = (I*a m ) / . We should convert the given unit values in milli inches per year.
Given, I = 1.69*10 -4 amp/cm 2
Atomic weight of iron = a m = 55.86 g/mol
n = number of electrons = 2 [Fe ==> Fe +2 +2e – ]
F = faraday’s constant = 96500 coulombs
d=density of iron = 7.875 g/cm 3
= [(1.96×10 -4 coulombs/sec*cm 2 ) × ] ÷ [(7.874 g/cm 3 ×2×96500 coulombs)]
= [(1.96×10 -4 coulombs /sec* cm 2 ) × ] ÷ [(7.874 g/ cm 2 *cm×2×96500 coulombs )]
= [(1.96×10 -4 1/sec) × ] ÷ []
= [1.69×10 -4 × × × 10 3 ] / [2 × 96500 × 7.875 × 2.54]
= 77.117 MPY.
11. _____ is used to measure the extent of uniform corrosion.
a) MDD
b) MPY
c) Both MPY and MDD
d) MPE
Answer: a
Explanation: Uniform corrosion is the corrosion that occurs throughout the entire exposed surface of a metal and it is uniform in depth of corrosion layer. Weight loss method I.e. MDD is used to know the extent of uniform corrosion.
12. Corrosion rate of aluminum is _________ when compared with corrosion of mild steel in open oxygenated atmosphere.
a) small
b) medium
c) large
d) very small
Answer: d
Explanation: In oxygenated atmosphere aluminum has high corrosion resistant than the mild steel due to its oxide layer formation. Hence the corrosion rate of aluminum is very small when compared to the corrosion rate of mild steel.
13. ___________ will occur, if current pass from an electrode to electrolyte.
a) Oxidation
b) Reduction
c) Oxidation and reduction
d) Anion formation
Answer: a
Explanation: The direction of current flow is exactly opposite to the movement of electrons. We know electrons starts at the anode and travels towards cathode whereas current will flow from anode to electrolyte. This results in oxidation or corrosion on that electrode.
14. Oxidizing impurities in electrolyte increases the corrosion rate.
a) True
b) False
Answer: a
Explanation: Mixed potential theory states that any electrochemical reaction can be divided into two or more partial reactions . Presence of oxidizing impurities such as Fe +3 increases the number of reduction reactions. It correspondingly increases the oxidation rate or corrosion rate.
15. What are the uses of corrosion rate estimation of materials in daily life?
a) To predict the life time of a component
b) To compare the corrosive-resistant of materials
c) To increases the corrosion rate
d) To predict the life time and to compare the corrosive resistant of materials
Answer: d
Explanation: Corrosion rate expression is used to quantify the corrosion process. This helps us to predict the life time of a component and to compare with different materials. This also helps us to change the process variables in order to decrease the corrosion rate.
This set of Corrosion Engineering Multiple Choice Questions & Answers focuses on “Corrosion Principles – Electrochemical Aspects – 1”.
1. Which of the following products are obtained when a zinc metal is dipped in dilute HCl solution?
a) H 2 , ZnCl 2
b) Cl 2 , ZnH 2
c) H 2 , Cl 2 and ZnH 2
d) Zn, H 2 and Cl 2
Answer: a
Explanation: When zinc is placed in dilute hydrochloric acid, a vigorous reaction occurs. Hydrogen gas is evolved and the zinc dissolves, by forming a solution of zinc chloride.
Anodic reaction: Zn==>Zn +2 +2e(Zn +2 +2Cl – ==>ZnCl 2 )
Cathodic reaction: 2H + +2e==>H 2
2. Which of the following reactions occurs when iron is immersed in sea water?
a) Fe==>Fe +2 +2e, 2H + +2e==>H 2
b) Fe==>Fe +2 +2e, O 2 +2H 2 O+4e==>4OH –
c) Fe +2 +2e==>Fe +2 , 4H + +O 2 +4e==>2H 2 O
d) Fe +2 +2e==>Fe +2 , 2H + +2e==>H 2
Answer: b
Explanation: Iron dissolution Fe==>Fe +2 +2e. Oxygenated hydrogen reaction in a neutral solution is O 2 +2H 2 O+4e==>4OH – .
3. Which of the following is more stable form of iron in an oxygenated solution?
a) Fe 2 O 3
b) Fe 2
c) 2Fe 3
d) Fe 3 O 4
Answer: c
Explanation: +3 oxidation state of iron is more stable state of iron than +2 oxidation state. The reaction is follows as
Fe+H 2 O+½O 2 ==>Fe 2
2Fe 2 +H 2 O+1/2O 2 ==>2Fe 3 .
4. Which of the following are the types of chemical reactions?
a) Combination and Decomposition reactions
b) Combination and Single displacement
c) Single and Double displacement reaction
d) Combination, Decomposition, Single displacement and double displacement
Answer: d
Explanation: Combination reaction: A+B==>C,
Decomposition reaction: A==>B+C,
Single displacement reaction: AB+C==>AC+B
Double displacement reaction: AB+CD==>AC+BD
5. More than one anodic and cathodic reactions are possible in corrosion.
a) True
b) False
Answer: a
Explanation: Mixed potential theory states that any electrochemical reaction can be divided into two or more partial reactions . Dissolution of an alloy in pure acid involves more than one anodic reaction. Corrosion of pure metal in oxygenated impure acid involves more than one cathodic reaction.
6. Oxygenated acids are more corrosive than oxygen-free acids.
a) True
b) False
Answer: a
Explanation: Case1
Anodic reaction: M==M> +n +ne
Cathodic reaction: 2H + +2e==>H 2
Case2
Anodic reaction: M==>M +n +ne
Cathodic reaction: 2H + +2e==>H 2 , O 2 +4H + +4e==>2H 2 O
This oxygen reduction increases the cathodic rate which correspondingly increases the anodic rate or corrosion rate.
7. Which of the following parameter of electrolyte decreases the corrosion rate?
a) Dissolved oxygen
b) Temperature
c) High electrical resistance
d) Presence of ferric ions
Answer: c
Explanation: The Function of an electrolyte is to transfer the ions between anode and cathode. Increase in electrical resistance in electrolyte shows obstruction for the free flow of ions, hence the corrosion rate decreases. Whereas dissolved oxygen, temperature and presence of ferric ions increases the mobility of ions and increases the corrosion rate.
8. Which of the following are the types of polarization?
a) Activation polarization
b) Activation and Concentration polarization
c) Resistance polarization
d) Activation, Concentration and Resistance polarization
Answer: d
Explanation: Polarization is the potential difference occurred due to the non-equilibrium conditions, due to the change in concentration or temperature. These are classified into three types. They are i) Activation polarization ii) Concentration polarization iii)Resistance polarization.
9. Which of the following is depicted in the given figure?
a) Activation polarization
b) Concentration polarization
c) Resistance polarization
d) Concentration and Resistance polarization
Answer: a
Explanation: Activation polarization refers to an electrochemical process that is controlled by the reaction sequence at the metal-electrolyte interface.
Step 1: Species adsorbed on the metal surface
Step 2: Electron transfer
Step 3: Reduction of species
Step 4: Combine to form a bubble of hydrogen molecule.
10. Which of the following is depicted in the given figure?
a) Activation polarization
b) Concentration polarization
c) Resistance polarization
d) Both Activation and Resistance polarization
Answer: b
Explanation: Concentration polarization refers to an electrochemical process that is controlled by the diffusion of ions from bulk solution to the metal-electrolyte interface. This usually occurs in low concentration electrolytes.
This set of Corrosion Engineering Questions and Answers for Freshers focuses on “Corrosion Principles – Electrochemical Aspects – 2”.
1. Concentration polarization is considered in both anodic and cathodic reactions.
a) True
b) False
Answer: b
Explanation: Concentration polarization refers to the electrochemical reaction that is controlled by the diffusion of ions in an electrolyte. This occurs in the low concentration of electrolyte. It is neglected in the case of anodic reaction because there is a sufficient supply of metal atoms in a metallic piece and there is no need for diffusion.
2. Which of the following polarization will be influenced by electrolytic agitation?
a) Activation polarization
b) Resistance polarization
c) Concentration polarization
d) Both Activation and Resistance polarization
Answer: c
Explanation: Concentration polarization refers to the electrochemical reaction that is controlled by the diffusion of ions in an electrolyte. With an increase in the velocity or agitation of the electrolyte the contact of ions with metal interface increases.
3. What is meant by passivation?
a) Loss of reactivity
b) Increase in reactivity
c) Increase in corrosion rate
d) Deterioration of metal
Answer: a
Explanation: Passivation is the state of metal in which stable films or barriers are formed. These stable films obstruct the contact of corrosive medium to the metal surface. Most of the engineering metals undergo passivation under different atmospheric conditions.
4. Which of the following metal is depicted in the given graph?
a) Active metal
b) Passive metal
c) Active-Passive metal
d) Trans passive state of metal
Answer: a
Explanation: The corrosion rate of active metal increases with an increase in the oxidizing potential of the environment. In the case of passive metal, it remains almost constant at a lower corrosion rate value. Whereas in the case of trans passive state of metal the corrosion increases from a certain value due to the damage of protective film.
5. Which of the following metal is depicted is in the given figure?
a) Active metal
b) Passive metal
c) Active-Passive transition metal
d) Trans passive state of metal
Answer: c
Explanation: Active-Passive transition metal is a metal that undergoes a transition from active to passive state after a certain oxidation potential. The oxidation potential from which the passivation starts is called critical oxidation potential. Fortunately, most of the engineering metals are active-passive metals that protect from corrosion.
6. What is the trans passive region?
a) Region after passive state
b) Formed by breakage of the protective film in the passive region
c) Constant corrosion rate
d) Region formed after passive state by breakage of the passive oxide layer
Answer: d
Explanation: Trans passive region is formed in an active-passive transition metal after crossing the limiting oxidizing potential after a passive region. This occurs due to the breakage of the protective layer due to the unbearable oxidizing potential of the corrosive medium.
7. Which of the following is denoted as // in an electrochemical cell notation?
a) Anode
b) Cathode
c) Electrolyte
d) Salt bridge
Answer: d
Explanation: Salt bridge is a connection between two half cells used to neutralize the ions with respective opposite charged ions. Usually, strong electrolytes such as KCl along with agar-agar gel are used.
8. Which of the following gives Standard cell potential of a cell (E o )?
a) E o cathode -E o anode
b) E o anode -E o cathode
c) E o cathode *E o anode
d) E o anode /E o cathode
Answer: a
Explanation: A electrochemical cell consist of two electrodes with a potential difference preferentially one acts as a cathode and other as an anode. The standard state of each specific electrode is constant and it measured against the hydrogen electrode at 25°C and 1 atm pressure. And standard cell potential is calculated as E o cathode -E o anode .
9. Which of the following is a Nernst equation?
a) E cell =E o cell –RT/nF ln
b) E cell =E o cell –nF/RT ln
c) E 0 cell =E cell –RT/nF ln
d) E 0 cell =E cell –nF/RT ln
Answer: a
Explanation: E cell =E o cell –RT/nF ln is the Nernst equation. E o cell is the potential of a cell in the standard state, R is Universal gas constant, n is the valency of ion, T is absolute temperature, F is Faraday’s constant and K is the reaction quotient, E cell is the cell potential.
Answer: a
Explanation: Chemical reaction can be written as Zn + 2Ag +1 ==>Zn +2 +2Ag
E o cell =0.80- (since E o silver=0.80V, E o zinc=-0.763V)
E o cell =1.563V
E cell =E o cell –RT/nF ln
E cell =1.563-[/2*96500)]ln
E cell =1.563-[/2*96500)]ln
E cell =1.563-[/2*96500)]ln
E cell =1.563+0.01283
E cell =1.57583 V.
This set of Corrosion Engineering Multiple Choice Questions & Answers focuses on “Corrosion Principles – Effect of Oxygen and Velocity”.
1. What is the nature of region number 1 in the given figure?
a) Active region
b) Passive region
c) Trans passive region
d) Active-Passive transition region
Answer: a
Explanation: The active region is the region in which the corrosion rate increases with an increase in oxidizer concentration. Iron in oxygenated water is the best example of an active region. Because iron will not undergo the transition to passive region irrespective of the concentration of oxygen present at room temperature.
2. What is the nature of region number 2 described in the given figure?
a) Active region
b) Passive region
c) Trans passive region
d) Active-Passive transition region
Answer: b
Explanation: The passive region is the region in which the corrosion rate is very less and even become independent with the concentration of oxygen. Hastelloy C in FeCl 3 solution is the best example of a passive state region.
3. What is the nature of region number 3 in the given figure?
a) Active region
b) Passive region
c) Trans passive region
d) Active-Passive transition region
Answer: c
Explanation: Trans passive transition is obtained from passive state due to the presence of a high concentration of oxidizers. This transition initiated with the breakage of protective films and it increases exponentially with the increase in oxidizer concentration.
4. Passivity is achieved only if a sufficient quantity of oxidizer is added to the medium.
a) True
b) False
Answer: a
Explanation: In practical cases, the corrosion rate is estimated based on the current density generated. We know that the current density increases with the increase in oxidizer concentration and passivity will only be achieved when the current density crosses critical current density value (i c ).
5. Which of the following metal-acid combination will shift metal from active to passive state with an increase in oxidizer concentration?
a) Monel in HCl+O 2
b) 18Cr-8Ni in H 2 SO 4 +Fe +3
c) Fe in H 2 O+O 2
d) 18Cr-8Ni in HNO 3 + Cr 2 O 3
Answer: b
Explanation: Initially corrosion rate of Stainless steel in sulfuric acid increases with an increase in the concentration of ferric ion (Fe +3 ). And then it is followed by a rapid decrease in corrosion rate due to the formation of a passive layer. Critical current density (i c ) must be achieved to undergo the transition from active to passive.
6. What is the nature of copper corrosion in oxygenated sulfuric acid?
a) Active region
b) Passive region
c) Active-Passive transition region
d) Trans-passive region
Answer: a
Explanation: Copper will act as an active metal in sulfuric acid, the corrosion rate increases with an increase in oxygen concentration. And the passivity is not achieved irrespective of the oxidizer added.
7. The corrosion rate depends on both the medium and the metal involved.
a) True
b) False
Answer: a
Explanation: We know that different metals will respond differently in the same medium. In another case, the same metal shows different characters in different mediums. Thus, the corrosion rate depends on both the medium and the metal involved in the reaction.
8. What is the other name of concentration polarization?
a) Anodic diffusion control
b) Cathodic diffusion control
c) Erosion corrosion
d) Activation polarization
Answer: b
Explanation: Concentration polarization is also called as cathodic diffusion control. Concentration polarization is controlled by the diffusion of ions from the bulk solution to the metal electrolyte interface. This diffusion can be accelerated by agitation or by increasing the velocity of the solution.
9. Which of the following metals are more corrosion resistant in a high-velocity corrosive solution?
a) Stainless steel
b) Lead
c) Titanium
d) Both stainless steel and titanium
Answer: d
Explanation: Stainless steel and titanium are easily passivating material and easily get passivated in high-velocity mediums. These metals form a stable oxide layer that can resist high velocities of corrosive medium.
10. Which of the following corrosion is indicated by the C curve in the given figure?
a) Uniform corrosion
b) Galvanic corrosion
c) Erosion corrosion
d) Stress cracking corrosion
Answer: c
Explanation: Erosion corrosion is the mechanical damage of the material due to the high velocity of the medium. The effect of agitation or velocity will have a negligible effect until the mechanical damage initiates.
11. Which of the following reaction is depicted by curve A in the given figure?
a) Fe in dilute HCl
b) Pb in dilute H 2 SO 4
c) 18Cr–8Ni in H 2 SO 4
d) 18Cr–8Ni in H 2 SO 4 +Fe +3
Answer: d
Explanation: Stainless steel in H 2 SO 4 with the impurity of ferric ions (Fe +3 ) follows curve A. Initially, the corrosion rate of stainless-steel increases with the increase in velocity up to critical current density (i c ). Then the corrosion rate of stainless-steel decreases rapidly and becomes almost constant due to passivation.
This set of Corrosion Engineering Interview Questions and Answers for freshers focuses on “Effect of Temperature and Corrosive Concentration”.
1. The rate of chemical reaction increases with an increase in temperature.
a) True
b) False
Answer: a
Explanation: Temperature increases the rate of almost all the reactions because it increases the kinetic energies of atoms or ions. This increase in kinetic energy makes them react to each other to get stable products. It also increases the mobility of ions in the electrolyte.
2. What is the corrosion rate behavior of curve A with the increase in temperature, described in the given figure?
a) Constant
b) Exponential increase
c) Exponential decreases
d) Slightly decreases
Answer: b
Explanation: Curves A and B represent the corrosion behavior of different materials with an increase in temperature. Here curve A indicates the exponential increase in corrosion rate with the temperature. Example: Iron in hydrofluoric acid.
3. What is the corrosion rate behavior of curve B with the increase in temperature, described in the given figure?
a) Exponential increase
b) Exponential decrease
c) Constant up to high temperatures
d) Slightly decreases
Answer: c
Explanation: Here curve B indicates the uniform corrosion rate up to very high temperatures, this is due to the formation of protective oxide layers. At very high temperatures, it results in the transformation of trans passive region which increases the corrosion rate exponentially.
4. In which of the following reactions, we observe the exponential increase in corrosion rate with an increase in temperature?
a) 18Cr-8Ni in H 2 SO 4
b) 18Cr-8Ni in HNO 3
c) Ni in NaOH
d) Monel in HF
Answer: a
Explanation: Stainless steel in sulfuric acid will corrode exponentially with the increase in temperature. Whereas stainless steel in nitric acid, nickel in sodium hydroxide, monel for hydrofluoric acid are the best corrosion-resistant materials in respective mediums and suffer less corrosion with the increase in temperature.
5. In which of the following reactions, we observe the unaffected corrosion rate with the increase in temperature?
a) 18Cr–8Ni in HNO 3
b) 18Cr-8Ni in H 2 SO 4
c) Ni in HCl
d) Fe in HF
Answer: a
Explanation: Stainless steel in the HNO 3 medium will have a negligible effect on the corrosion rate with the increase in temperature. It forms a stable oxide layer and avoids the exposure of a corrosive atmosphere to the metallic surface. It is stable up to very high temperatures.
6. What is the corrosion rate behavior of curve B with the increase in corrosive concentration, described in the given figure?
a) Exponential increases
b) Exponential decreases
c) Constant
d) First increases and then decreases
Answer: d
Explanation: The given figure represents the corrosion behavior of different materials with an increase in the concentration of the corrosive medium. Curve B represents the group of materials where the corrosion rate increases rapidly at first and then decreases with increases in corrosive concentration. This is due to the 1. formation of the passive layer 2. decrease in the ionization of acids.
7. What is the corrosion rate behavior of curve A with the increase in corrosive concentration, described in the given figure?
a) Almost constant
b) Exponential increase
c) Exponential decrease
d) First increases and then decreases
Answer: a
Explanation: Curve A represents the group of materials in which an increase in corrosive concentrations has a negligible effect on it until very high concentrations are reached. This is due to the formation of the passive layer. After that, it results in mechanical damage at very high corrosive concentrations.
8. The concentration of the corrosive medium increases with the increase in impurity ion concentration.
a) True
b) False
Answer: a
Explanation: Concentration of corrosive medium depends on the concentration of impurity ions present in it. General impurities are dissolved oxygen, ferric ions, and many other metal oxides.
9. In which of the following reactions, we observe an increase in corrosion rate with the increase in corrosive concentration?
a) 18Cr–8Ni in HNO 3
b) Ni in NaOH
c) Pb in H 2 SO 4
d) Fe in H 2 SO 4
Answer: d
Explanation: Iron in sulfuric acid, the corrosion rate of iron increases at first and then it decreases with an increase in corrosive concentration. This is because, at low concentrations, iron will dissolve in sulfuric acid whereas at high concentrations it forms a passive layer on the sample surface.
Answer: b
Explanation: Nickel in caustic soda is the best corrosive resistant material at various corrosive concentrations. Thus, it shows a negligible change in the corrosion rate even with the increase in the corrosive concentration.
Sanfoundry Global Education & Learning Series – Corrosion Engineering.
This set of Corrosion Engineering Multiple Choice Questions & Answers focuses on “Principles – Effect of Galvanic Coupling”.
1. The effect of Galvanic Coupling is due to the contact of dissimilar metals in a conductive electrolyte.
a) True
b) False
Answer: a
Explanation: If two dissimilar metals are placed in contact with each other in a conductive electrolyte, the potential difference produces electron flow between them. This results in the acceleration of preferential anode dissolution. This is known as the effect of Galvanic coupling.
2. What are the factors that affect Galvanic coupling?
a) Type of metals
b) Relative size of electrodes
c) Environmental conditions
d) Types of metals, the relative size of electrodes and environmental conditions
Answer: d
Explanation: Metal combinations used for galvanic contact will affect based on the potential difference between them. Relative size of electrodes, environmental conditions such as temperature, humidity and salinity alter the chemical kinetics of the reaction.
3. Preferential cathode and anode are formed based on the potential value of a metal electrode.
a) True
b) False
Answer: a
Explanation: Electrode with relatively high reduction potential preferentially act as a cathode and the other electrode will act as an anode. The effect of galvanic coupling can be minimized by selecting metal combinations with less potential difference.
4. Which of the following type of corrosion is depicted in the given figure?
a) Uniform corrosion
b) Erosion corrosion
c) Galvanic corrosion
d) Crevice corrosion
Answer: c
Explanation: Galvanic corrosion is an electrochemical corrosion in which preferential anode will corrode rapidly due to the effect of galvanic coupling.
5. In which of the following cases, we observe the galvanic effect?
a) Bolts and Nuts metal joining’s
b) Piping arrangements
c) Machinery of a different metal combination
d) Bolts and nuts metal joining’s, piping arrangements and machinery of a different metal combinations
Answer: d
Explanation: The galvanic effect is due to the contact of two dissimilar metals in a conductive solution. The corrosion caused due to galvanic effect is known as galvanic corrosion. It can be usually observed at bolts and nuts metal joining’s, piping arrangements and machinery of different metal combinations.
6. What is the abbreviation of SHE?
a) Substitute hydrogen electrode
b) Standard hydrogen electrode
c) Significant hydrogen electrode
d) Standard hydride electrode
Answer: b
Explanation: SHE means a Standard hydrogen electrode. It is used to calculate the potential of other elements by arbitrarily defined as zero. The standard conditions of SHE is 1 atm pressure of H 2 gas, 25°C temperature and non-corroding conditions for pure metals.
7. Which of the following are Reference electrodes?
a) Standard hydrogen electrode
b) Calomel electrode
c) Silver electrode
d) Standard hydrogen electrode and a calomel electrode
Answer: d
Explanation: In EMF series all metals are referenced against the hydrogen electrode (H 2 /H+) which is arbitrarily defined as zero. This is known as the Standard hydrogen electrode . The saturated calomel electrode also acts as a reference electrode based on the reaction between elemental mercury and mercury chloride (Hg 2 Cl 2 ). And the electrode potential value of the calomel electrode is +0.241 V.
8. Which of the following is/are the characteristics of a Galvanic series?
a) Used only for pure metals
b) Less accurate prediction than EMF series
c) Includes active and passive potentials of a metal
d) Measured only at room temperature
Answer: c
Explanation: Galvanic series is the arrangement of various engineering materials in a decreasing reduction potential value in seawater. Galvanic series is more accurate than EMF series and it can be measured at various temperatures of a specific medium. It includes the active state potential and passive state potential of a metal.
9. Which of the following is/are the preventions of the galvanic effect?
a) Insulating dissimilar metals
b) Selection of close metal combinations in a galvanic series
c) Neglecting area effect
d) Insulating dissimilar metals and selection of close metal combinations in a galvanic series
Answer: d
Explanation: The galvanic effect is due to the contact of two dissimilar metals in a conductive solution. It can be minimized by insulating dissimilar metals with non-conductive materials. And it can be reduced by the selection of close metal combinations in a galvanic series.
10. Which of the following effect is described in the given figure?
a) Crevice
b) Pitting
c) Beneficial galvanic effect
d) Erosion
Answer: c
Explanation: The galvanic effect is due to the contact of two dissimilar metals in a conductive solution. Here beneficial galvanic effect takes place as zinc is corroding preferentially by protecting steel.
This set of Corrosion Engineering Questions and Answers for Experienced people focuses on “Principles – Metallurgical and Other Aspects”.
1. Which of the following are the types of materials, that are categorized based on its atomic arrangement?
a) Crystalline
b) Amorphous
c) Semi-crystalline
d) Crystalline, amorphous and semi-crystalline
Answer: d
Explanation: The atoms in the crystalline materials are regularly arranged with the same repeating unit in a long-range order. Examples of crystalline materials are metals.
The atoms in which the atoms are not regularly arranged over a long-range are called amorphous materials. Example: Glass, rubbers.
Whereas semi-crystalline is the combination of both crystalline and amorphous materials.
2. What is the crystal structure of Austenitic stainless steel?
a) Face centered cubic structure
b) Body-centered cubic structure
c) Hexagonal close packed structure
d) Simple cubic structure
Answer: a
Explanation: Austenitic stainless steel is an alloy of iron, chromium, and nickel. Due to the high content of chromium, the resultant stabilizes in the austenitic phase. Austenite usually exists in the FCC crystal structure.
3. What is the crystal structure of Magnesium?
a) Face centered cubic structure
b) Body-centered cubic structure
c) Hexagonal close packed structure
d) Simple cubic structure
Answer: c
Explanation: HCP is abbreviated as hexagonal close packed structure. Conditions for HCP is a 1 =a 2 ≠a 3 and α=β=60, Îł̈=120, where a 1 , a 2 , a 3 are unit vectors in three directions and α, β, Îł̈ are angles between them. Magnesium possesses an HCP crystal structure.
4. Which of the following crystal structure is depicted in the given figure?
a) Face centered cubic structure
b) Hexagonal close packed structure
c) Body-centered cubic structure
d) Simple cubic structure
Answer: c
Explanation: Simple cubic structure is a cube with lattice atoms only at the corners.
Face centered cubic structure is a cube with lattice atoms at the corners along with at the centers of cubic faces.
BCC is abbreviated as a Body-centered cubic structure. It is a cube with lattice atoms at the corner along with a single atom at the center of the cube.
5. Which of the following is/are the properties of metals?
a) Ductility
b) Electrical conductivity
c) Thermal conductivity
d) Ductility, electrical and thermal conductivity
Answer: d
Explanation:
Ductility, malleability, conductors of heat and electricity, lustrous, definite melting and boiling point, lustrous, high strength, sonorous, etc are the properties of metals.
6. Which of the following types of bonds are non-directional in nature?
a) Covalent bond
b) Ionic bond
c) Metallic bond
d) Covalent and metallic bond
Answer: d
Explanation: Non-directional bonding is a type in which each atom is bonded to many of its neighbors. Covalent and metallic bonds are non-directional in nature whereas ionic bond is directional in nature.
7. Grain boundaries are the mismatch regions formed between two grains during solidification.
a) True
b) False
Answer: a
Explanation: Every metal microstructure consists of grains and grain boundaries. Grain boundaries are high energy areas, formed due to the mismatch between the grains during the solidification.
8. Which of the following is an example of a homogenous alloy?
a) 18-8 stainless steel
b) Low carbon steel
c) High carbon steel
d) Spheroidal cast iron
Answer: a
Explanation: Homogenous alloy is the alloy in which the components are completely soluble in each other and it has only one phase. 18-8 stainless steel is a homogenous alloy with uniform composition and a single-phase structure.
9. Which of the following is an example of Heterogenous alloy?
a) High carbon steel
b) 18-8 stainless steel
c) Ni-Cu alloy
d) Bronze
Answer: a
Explanation: Heterogenous alloy is the alloy in which the components are partially dissolved in each other and it has two or more phases. High carbon steel consists of alpha iron, cementite phase, and lamellar structure.
10. Grain boundaries are highly prone to corrosion than the grain faces.
a) True
b) False
Answer: a
Explanation: Grain boundaries are the high energy area and are more active chemically. Hence, grain boundaries are highly prone to corrosion than the grain faces. This is used to develop a contrast between grain and grain boundaries in the inspection of microstructure.
11. Which of the following type of alloys are highly corrosion resistant in nature?
a) Homogenous alloys
b) Heterogenous alloys
c) Homogenous and heterogeneous alloys
d) Precipitation strengthened alloys
Answer: a
Explanation: Homogenous alloys are highly corrosion resistant alloys than other alloy types. Since the galvanic effect is not present in homogenous alloys because of its single phase.
12. Which of the following conditions are applied to the orthorhombic crystal structure?
a) a 1 =a 2 =a 3 and α=β=\
a 1 =a 2 ≠a 3 and α=β=\
a 1 ≠a 2 ≠a 3 and α=β=\
a 1 ≠a 2 ≠a 3 and α=β=\(\ddot{\gamma}\)≠90
Answer: c
Explanation: Crystal structures are divided into 14 different types based on the structure of the unit cell and arrangement of atoms in it. These 14 different types are called Bravais lattice. And the conditions for orthorhombic crystal structure is a 1 ≠a 2 ≠a 3 and α=β=Îł̈=90
, where a 1 , a 2 , a 3 are unit vectors in three directions and α, β, Îł̈ are angles between them.
13. Which of the following is the correct option regarding the packing efficiency of crystal structures?
a) FCC=HCP>BCC
b) FCC>HCP=BCC
c) FCC<BCC<HCP
d) HCP>FCC>BCC
Answer: a
Explanation: Packing efficiency = *100. Packing-efficiency of FCC, HCP, and BCC is 74%, 74%, and 68%. Therefore, the correct order is FCC=HCP>BCC.
14. What is the ROI in economic consideration of corrosion?
a) Refund on investment
b) Return on investment
c) Refund on income
d) Return on income
Answer: b
Explanation: ROI means Return on investment.
ROI=[(O a +I a /n a )–(O b +I b /n b )/I b –I a ]*100 where O = annual costs including maintenance cost, I=Investment, n=anticipated life in years, and subscripts a and b refer to the present and proposed installations, respectively.
15. What is NPV in economic consideration of corrosion?
a) Net profit volume
b) Net present value
c) Net profit value
d) Net precision value
Answer: b
Explanation: NPV provides the most accurate basis for analyzing business costs and can be directly applied to the economics of corrosion control. But it needs extensive calculations.
This set of Corrosion Engineering Multiple Choice Questions & Answers focuses on “Eight Forms – Uniform Corrosion”.
1. What is the important basis for the classification of corrosion?
a) Appearance of corroded metal
b) Nature of metal
c) Environmental conditions
d) Corrosion rate
Answer: a
Explanation: The basis for the classification of corrosion is the appearance of corroded metal. Each form can be identified by visual observation as it has a unique form of appearance.
2. Which of the following is/are types of corrosion?
a) Erosion corrosion
b) Galvanic corrosion
c) Pitting corrosion
d) Erosion, galvanic and pitting corrosion
Answer: d
Explanation:
Types of corrosion: i. Uniform corrosion
ii. Galvanic corrosion
iii. Crevice corrosion
iv. Pitting corrosion
v. Intergranular corrosion
vi. Selective leaching
vii. Erosion corrosion
viii. Stress corrosion
3. Which of the following type of corrosion is depicted in the given figure?
a) Pitting corrosion
b) Uniform corrosion
c) Erosion corrosion
d) Selective leaching
Answer: b
Explanation: Uniform corrosion is an electrochemical corrosion in which metal undergoes uniform depth of deterioration over its entire exposed surface. Example: Rusting of iron in atmospheric air.
4. Which of the following is an example of uniform corrosion?
a) Zinc dissolution in dilute H 2 SO 4
b) Dezincification of brass in acids
c) Rusting of iron
d) Zinc dissolution in dilute H 2 SO 4 and rusting of iron
Answer: d
Explanation: Uniform corrosion is characterized by an electrochemical reaction that proceeds uniformly over the entire exposed surface. Zinc dissolution in dilute H 2 SO 4 and rusting of iron are examples of uniform corrosion. Dezincification of brass in acids is an example of selective leaching.
5. Tarnishing of silver is an example of which type of corrosion?
a) Crevice corrosion
b) Pitting corrosion
c) Uniform corrosion
d) Erosion corrosion
Answer: c
Explanation: Outermost layers of silver undergoes a chemical reaction with hydrogen sulfide results in tarnish. This is known as the tarnishing of silver. Metals like brass, copper, aluminum, silver, and magnesium undergoes tarnishing under various corrosive environments.
6. What is/are the preventions of uniform corrosion?
a) Proper material coatings
b) Inhibitors
c) Cathodic protection
d) Proper material coatings, inhibitors, and cathodic protection
Answer: d
Explanation: Uniform corrosion can be prevented by proper material coatings, inhibitors, and cathodic protection. Proper material coatings minimize the exposure area of metal. An inhibitor is a chemical substance that decreases the corrosion rate of metal by modifying the surface of anode or cathode.
7. Which of the following is/are the causes of catastrophic failures of corrosion?
a) Incomplete weld penetration
b) Extremely porous casting
c) Improper heat treatment
d) Incomplete weld penetration, extremely porous casting and improper heat treatment
Answer: d
Explanation: Corrosion is an electrochemical reaction that results in the degradation of a material. Corrosion failures are usually catastrophic in nature. And the causes are incomplete weld penetration, extremely porous casting, and improper heat treatment.
8. What is the standard electrode potential of Fe +2 /Fe?
a) 0.0 V
b) +0.36
c) -0.44
d) -0.76
Answer: c
Explanation: Standard reduction potential of hydrogen ion, copper, iron, and zinc Is 0.0V, +0.36V, -0.44V and -0.76V respectively. These are measured against the standard hydrogen electrode which arbitrarily defined as zero.
9. Pure metals are more corrosion resistant than commercial materials.
a) True
b) False
Answer: a
Explanation: In most of the cases of corrosion, pure metals are more corrosion resistant than commercial materials. This is due to the absence of galvanic effect and selective leaching in pure metals.
10. Which of the following are the types of metallic coatings that prevent corrosion?
a) Metal cladding
b) Electroplating
c) Metal coat extrusion
d) Metal cladding, electroplating and metal coat extrusion
Answer: d
Explanation: Corrosion is an electrochemical reaction that results in the degradation of a material. It can be prevented by various metal coating methods such as metal cladding, electroplating and metal coat extrusion.
This set of Corrosion Engineering Multiple Choice Questions & Answers focuses on “Eight Forms – Galvanic Corrosion – 1”.
1.What is the other name of galvanic corrosion?
a) Bi-metallic corrosion
b) Mono-metallic corrosion
c) Localized corrosion
d) Mono-metallic and localized corrosion
Answer: a
Explanation: Galvanic corrosion can be termed as bi-metallic corrosion or two-metal corrosion. This is because the driving force for current transfer and corrosion is the potential developed between the two metals.
2. Corrosion of less corrosion-resistant metal is usually increased and the attack of the more corrosion-resistant is decreased in galvanic corrosion.
a) True
b) False
Answer: a
Explanation: As galvanic corrosion is a bi-metallic corrosion, relatively less corrosion-resistant metal preferentially acts as anode and relatively high corrosion-resistant metal preferentially acts as a cathode. This increases attack on the less corrosion-resistant metal and decreases on high corrosion-resistant metal .
3. Which of the following is the driving force in galvanic corrosion?
a) Conductivity of electrolyte
b) Crystal structure of metals
c) The potential difference between the two metals
d) Temperature of electrolyte
Answer: c
Explanation: The principle driving force for current transfer and corrosion is the potential developed between the two metals. This potential difference can be altered by various factors such as conductivity of electrolyte and temperature of the electrolyte.
4. Which of the following will act as cathode and anode respectively in a dry-cell battery?
a) Zinc and carbon
b) Carbon and zinc
c) Magnesium and zinc
d) Zinc and ammonium chloride
Answer: b
Explanation: Battery is a combination of cells in which chemical energy is converted into electrical energy. Carbon acts as cathode and zinc acts as an anode. Moist ammonium chloride is used as an electrolyte.
5. Which of the following is the primary characteristic of an electrolyte to form corrosion?
a) Electrical resistivity
b) Thermal resistivity
c) Thermal conductivity
d) Electrical conductivity
Answer: d
Explanation: Electrical conductivity is the primary characteristic of an electrolyte. Electrolyte is a medium to transfer electrons from anode to cathode, this results in corrosion. The conductivity of the electrolyte is one of the main factors in the regulation of corrosion.
6. What are the conditions to measure the standard reduction potential of metals against SHE?
a) 2 atm pressure, 25°C temperature, 2M concentration of H +
b) 2 atm pressure, 25°C temperature, 1M concentration of H +
c) 1 atm pressure, 25°C temperature, 1M concentration of H +
d) 1 atm pressure, 25°C temperature, 2M concentration of H +
Answer: c
Explanation: The conditions to measure the standard reduction potential of metal electrodes against standard hydrogen electrode are 1 atmospheric pressure, 25°C temperature and 1 molarity concentration of H + ions.
7. What is the standard reduction potential value of gold in the EMF series?
a) +1.498 V
b) +1.2 V
c) +0.987 V
d) +0.799 V
Answer: a
Explanation: Standard reduction potential values of metal are measured against SHE.
Standard reduction potential of gold (Au-Au +3 ), platinum (Pt-Pt +2 ), palladium (Pd-Pd +2 ), silver (Ag-Ag +1 ) are +1.498V, +1.2V, +0.987V and +0.799V respectively.
8. What is the standard reduction potential value of potassium in the EMF series?
a) +0.337 V
b) -2.925 V
c) -0.763 V
d) -1.662 V
Answer: b
Explanation: Standard reduction potential values of metal are measured against SHE, which is arbitrarily defined as zero. Standard reduction potential of potassium (K-K + ), aluminum (Al-Al +3 ), zinc (Zn-Zn +2 ), copper (Cu-Cu +2 ) are –2.925V, -1.662V, -0.763V and +0.337V respectively.
9. What is the abbreviation of EMF?
a) Electromagnetic force
b) Electromotive frequency
c) Electromotive force
d) Electrode motive force
Answer: c
Explanation: EMF is abbreviated as an electromotive force. It is defined as the potential difference between two points in a circuit. It is the cause of the flow of current in the circuit.
10. Which of the following electrolyte is used for the preparation of a general galvanic series?
a) Polluted seawater
b) Unpolluted river water
c) Polluted river water
d) Unpovlluted seawater
Answer: d
Explanation: Galvanic series is the most accurate prediction of galvanic relationships of metals. It is based on potential measurements and galvanic corrosion tests in unpolluted seawater. This includes metals and alloys along with their active and passive states.
11. Which of the following metal combination has a minimum galvanic effect?
a) Monel and copper
b) Inconel and Inconel
c) 18-8 stainless steel and 18-8 stainless steel
d) Titanium and lead
Answer: a
Explanation: The galvanic effect can be reduced by selecting close metal combinations. The position of a metal or an alloy in galvanic is mainly affected by its composition and its state . Monel and copper is the close metal combination, hence it has a minimum galvanic effect.
12. What does the square bracket [] in the galvanic series indicates?
a) Most practical metal combinations
b) High corrosion-resistant metals
c) Low corrosion-resistant metals
d) Avoidable metal combinations
Answer: a
Explanation: The bracket in the galvanic series indicates the most practical metal combinations. This metal combination results in little danger of galvanic corrosion.
Example: [ Monel, bronzes, copper, brasses]
13. The potential generated by two dissimilar metal combinations can change with time.
a) True
b) False
Answer: a
Explanation: The potential developed between two dissimilar metals is usually decreases. This is due to the accumulation of reaction or corrosion products at the anode or cathode. This results in a reduction of corrosion kinetics.
14. Which of the following is the most corrosion-resistant metal at room temperature?
a) Titanium
b) Platinum
c) Gold
d) Tantalum
Answer: d
Explanation: Tantalum is the most corrosion-resistant metal at room temperature. It is a rare, hard and lustrous transition metal. It is denoted by Ta and its atomic number is 73.
15. Which of the following corrosion is depicted in the given figure?
a) Crevice corrosion
b) Pitting corrosion
c) Galvanic corrosion
d) Uniform corrosion
Answer: c
Explanation: Voltaic cell is the cell in which chemical energy is converted into electrical energy by participating in redox reactions. In this cell, preferential cathode and anode are formed and the galvanic effect is observed. Thus, galvanic corrosion is depicted in the given figure.
This set of Corrosion Engineering Interview Questions and Answers for Experienced people focuses on “Eight Forms – Galvanic Corrosion – 2”.
1. The reason for the noble nature of titanium is that it cathodically polarizes readily in seawater.
a) False
b) True
Answer: b
Explanation: Titanium is one of the noble metals in the galvanic series and the reason is that it cathodically polarizes readily in seawater. It replaces many materials as best corrosive resistant metal in the seawater applications and high-velocity corrosive solutions.
2. Corrosion is greater near the seashore than in a dry rural atmosphere.
a) True
b) False
Answer: a
Explanation: Corrosion occurs due to the presence of oxygen and moisture . The electrical conductivity of the electrolyte is one of the factors of corrosion. Corrosion increases with an increase in electrical conductivity of the electrolyte. Moisture with salt content relatively has high electrical conductivity, hence corrosion is greater at the seashore.
3. Define the distance effect regarding galvanic corrosion?
a) Corrosion occurs only at the junction of two metals
b) Corrosion occurs only at the edges of two metals
c) Corrosion decreases with increase in distance from the junction
d) Corrosion increases with increase in distance from the junction
Answer: c
Explanation: The galvanic effect is the potential difference formed between two or more metals at its junction. It decreases on moving away from the junction. Hence corrosion decreases with an increase in distance from the junction.
4. Define area effect regarding galvanic corrosion?
a) cathodic area * anodic area
b) anodic area/cathodic area
c) cathodic area/anodic area
d) cathodic area + anodic area
Answer: c
Explanation: It is the ratio of cathodic to anodic areas. An unfavorable area ratio with a large cathodic area and small anodic area results in high current density at the anode. The greater the current density at an anodic area the greater the corrosion rate.
5. Which of the following is/are the preventions of galvanic corrosion?
a) Avoid the unfavorable area effect of a small anode and large cathode
b) Select the close combination of metals in galvanic series
c) Select the far combination of metals in galvanic series
d) Avoid the unfavorable area effect of a small anode and large cathode and select the close combination of metals in galvanic series
Answer: d
Explanation: In industrial applications avoiding a dissimilar metal combination is impossible. But it can be minimized by avoiding the unfavorable area effect, selecting the close combination of metals. Proper material selection and regular inspection are other preventive measures.
6. Which of the following principle is utilized in the concept of cathodic protection?
a) Principle of galvanic corrosion
b) Principle of crevice corrosion
c) Principle of pitting corrosion
d) Principle of selective leaching
Answer: a
Explanation: Cathodic protection is a protection of a base structure metal by making it as a cathode. It can be protected by the use of sacrificial anode. The order of metals in the galvanic series is the basis for cathodic protection.
7. Which of the following is an example of cathodic protection?
a) Electroplating of steel
b) Galvanization of steel
c) Magnesium connected to steel pipes
d) Electroplating of steel, galvanization of steel and magnesium connected to steel
Answer: d
Explanation: Electroplating and galvanization are cathodic protections of steel based on the galvanic effect. If steel under zinc or other metal coating exposed to corrosive atmosphere, zinc corrodes preferentially than steel. Magnesium acts as a sacrificial anode when it is connected to underground steel pipes.
8. Which of the following are the limitations of the EMF series?
a) Available for metals and alloys
b) Limited to pure metals only
c) Measured only at standard conditions
d) Limited to pure metals and measured only at standard conditions
Answer: d
Explanation: EMF series is a list of pure metals arranged according to their electrode potential value measured against SHE. It is measured at standard conditions such as 25°C, 1atm pressure, and 1M concentration of hydrogen ions.
9. Which of the following chemical is responsible for the stains on silver?
a) Hydrogen peroxide
b) Hydrogen sulfide
c) Sulfur dioxide
d) Sulfur trioxide
Answer: b
Explanation: The stains on sliver is usually due to the presence of hydrogen sulfide. It can be removed by the application of galvanic corrosion. It can be done with silver-aluminum galvanic attachment in the presence of baking soda.
10. Which of the following type of corrosion is depicted in the given figure?
a) Crevice corrosion
b) Pitting corrosion
c) Galvanic corrosion
d) Erosion corrosion
Answer: c
Explanation: Here zinc and iron preferentially act as the anode and cathode respectively. This is the galvanic effect. And zinc corrodes more rapidly and iron gets protected.
This set of Corrosion Engineering Multiple Choice Questions & Answers focuses on “Eight Forms – Crevice Corrosion”.
1. Which of the following is/are the reasons for the cause of crevice corrosion?
a) The stagnant solution in the holes and gasket surfaces
b) The stagnant solution in the lap joints and surface deposits
c) Dissimilar metal contact
d) The stagnant solution in the holes, gasket surfaces, lap joints, and surface deposits
Answer: d
Explanation: Crevice corrosion is a type of corrosion in which dissolution of metal is due to the presence of stagnant solution in the small gaps such as holes, gasket surfaces, lap joints, and surface deposits, etc.
2. Which of the following type of corrosion is localized in nature?
a) Crevice corrosion
b) Galvanic corrosion
c) Uniform corrosion
d) Inter-granular corrosion
Answer: a
Explanation: Crevice corrosion is localized corrosion because it occurs only at discrete sites on the metal surface. This occurs due to the presence of a stagnant solution in crevices . This crevice corrodes rapidly by cathodically protecting adjacent surfaces.
3. Which of the following is the other name of crevice corrosion?
a) Filiform corrosion
b) Deposit or gasket corrosion
c) Two-metal corrosion
d) Surface corrosion
Answer: b
Explanation: Crevice corrosion occurs due to the presence of a stagnant solution in the crevices. These crevices are formed due to the corrosion deposits or gaps at the metal-gasket interface. Thus, it is also called as deposit or gasket corrosion.
4. Which of the following metal is more susceptible to crevice corrosion?
a) Titanium
b) Hastelloy C
c) Stainless steel-430
d) Titanium and stainless steel
Answer: c
Explanation: Stainless steel-430 is highly prone to crevice corrosion. The reasons are as follows:
1. Large critical current density
2. Wide active-passive transitions
3. Limited passive region
5. Which of the following combination results in crevice corrosion?
a) Metal and absorbent gaskets
b) Continuous weld metals
c) Metal and non-absorbent gaskets
d) Single metal piece
Answer: a
Explanation: Metal and absorbent gasket combination results in the crevice corrosion. Absorbent gaskets absorb water vapor from surrounding and make them stagnant at the metal–gasket interface. This results in crevice corrosion.
6. Which of the following characteristics of the crevice is a must to act as a corrosion site?
a) It should be wide enough to permit liquid entry
b) It should be narrow enough to maintain a stagnant zone
c) It should be wide enough to avoid a stagnant zone
d) It should be wide enough to permit liquid entry and narrow enough to maintain a stagnant zone
Answer: d
Explanation: Crevice is a small volume region formed between the interface of metal and gaskets. It acts as a corrosion site if is wide enough to permit liquid entry and narrow enough to maintain a stagnant zone.
7. What is the primary condition regarding the velocity of an electrolyte to form crevice corrosion?
a) The velocity of the electrolyte should be greater than 10cm/s
b) The velocity of the electrolyte should be less than 10cm/s
c) The velocity of the electrolyte should be equal to 10cm/s
d) The stagnant electrolytic solution should be present
Answer: d
Explanation: Crevice corrosion occurs due to the presence of stagnant electrolytic solution in the crevices. It acts at the corrosion sites and it results in the formation of localized corrosion. An increase in the velocity of the electrolyte decreases the extent of crevice corrosion.
8. The difference in metal ion or oxygen concentration between the crevice and its surroundings is the main reason for crevice corrosion.
a) True
b) False
Answer: a
Explanation: Crevice corrosion is mainly occurred due to the difference in metal ion or oxygen concentration between the crevice and its surroundings. This is due to the unavailability of oxygen in the crevice, this results in the dissolution of metal in a crevice by protecting adjacent surface cathodically.
9. Which of the following chemical reaction that usually occurs in the crevice?
a) M + +H 2 O=MOH
b) M + +Cl – =MCl
c) M + Cl – +H 2 O=MOH +H + Cl –
d) 4OH – =O 2 +2H 2 O+4e –
Answer: c
Explanation: As the metallic ion concentration increases in the crevice, the migration of chloride ions takes place to neutralize that. After that, metal chlorides undergo hydrolysis and results in the formation of insoluble metal hydroxide and free acid.
10. Which of the following ions that accelerate the dissolution rate of metals or alloys in a crevice?
a) H + , OH –
b) H + , Cl –
c) OH – , Cl –
d) OH – , Cl – and H –
Answer: b
Explanation: H + and Cl – ions accelerate the dissolution rate of metals and alloys in the crevice. These are produced by hydrolysis of metal chlorides. It accelerates corrosion because hydrogen ion decreases pH value and chloride ion attacks the metallic surface in the crevice.
11. Which of the following metal is highly resistant to crevice corrosion?
a) Stainless steel
b) Copper
c) Aluminum
d) Hastelloy C-276
Answer: d
Explanation: Hastelloy C-276 is the best crevice corrosion-resistant metal. The composition of Hastelloy C-276 is 15.5%Cr, 54.7%Ni, 15.5%Mo, 3.8%W, and 0.5%Mn. Whereas the other metals depend on oxide film for their corrosion resistance.
12. As the metal dissolution within the crevice increases, the rate of oxygen reduction on adjacent surfaces increases.
a) True
b) False
Answer: a
Explanation: Metallic dissolution in the crevice cathodically protects the external surface. Electrons transfer from M==>M +n +ne to compensate O 2 +H 2 O+4e==>4OH .
13. What is the incubation period associated with a crevice attack?
a) 1 month – 10 months
b) 1 hour – 10 hours
c) 1 day – 10 days
d) 6 months – 1 year
Answer: d
Explanation: The incubation period is the time required to initiate the crevice corrosion on metal. It usually in the range of 6 months to 1 year. It depends on many factors such as the material used, corrosive medium, temperature, etc.
14. Metals or alloys that depend on oxide films for corrosive resistance are highly susceptible to crevice corrosion.
a) True
b) False
Answer: a
Explanation: Metals or alloys that depend on oxide films for corrosive resistance are highly susceptible to crevice corrosion. These passive films are destroyed by high concentrations of hydrogen and chloride ions, and the metallic dissolution increases rapidly.
15. Which of the following type of corrosion is depicted in the given figure?
a) Galvanic corrosion
b) Uniform corrosion
c) Crevice corrosion
d) Pitting corrosion
Answer: c
Explanation: Crevice corrosion is localized corrosion that occurs due to the formation of crevices on various metal or gasket junction. A crevice will act as a corrosion site when it is wide enough to permit liquid entry and narrow enough to maintain a stagnant zone.
This set of Corrosion Engineering Multiple Choice Questions & Answers focuses on “Eight Forms – Filiform Corrosion”.
1. Which of the following characteristics of active-passive metal will acquire optimize crevice corrosion resistance?
a) A narrow active-passive transition
b) A small critical current density
c) An extended passive region
d) A narrow active-passive transition, a small critical current density, and an extended passive region
Answer: d
Explanation: The optimum crevice corrosion resistance of active-passive transition metal is acquired by having the following characteristics: i. A narrow active-passive transition
ii. A small critical current density
iii. An extended passive region
2. Which of the following corrosion testing describe the test for crevice corrosion?
a) Occluded cell corrosion
b) Galvanic effect
c) Atmospheric exposure testing
d) Kesternich chamber testing
Answer: a
Explanation: Occluded cell corrosion is a corrosion testing that describes crevice corrosion. In this test, a narrow gap is maintained between two metal in a stagnant corrosive solution. An occluded cell is also known as crevice corrosion.
3. The incubation period is the amount of time required to initiate crevice corrosion on a corrosive site.
a) True
b) False
Answer: a
Explanation: The incubation period is the time required to initiate the crevice corrosion on a corrosive site. It depends on many factors such as
i. Type of crevice formed
ii. Nature of material used
iii. Temperature
iv. The difference in the concentration of oxygen in the crevice and its surroundings
4. The crevice corrosion index is an index is to assist the selection of materials for construction.
a) True
b) False
Answer: a
Explanation: Crevice corrosion index is developed by Streicher. CCI is an index used to assist the selection of materials for construction. It minimizes the chances of crevice formation by proper material selection.
5. Which of the following are the methods and procedures to minimize crevice corrosion?
a) Use of welded joints instead of riveted joints
b) Avoid sharp edges and stagnant areas
c) Removal of deposits frequently
d) Use of welded joints instead of riveted joints, avoid sharp edges and stagnant areas and removal of deposits frequently
Answer: d
Explanation: Combating or minimizing crevice corrosion can be done as follows:
l. Use of welded joints instead of riveted or bolted joints
ll. Avoid sharp edges and stagnant areas
lll. Regular inspection
lV. Removal of deposits frequently
V. Use of non-absorbent gaskets
6. Which of the following is a non-absorbent gasket?
a) Polyethylene
b) Isoprene
c) Teflon
d) Polyethylene and isoprene
Answer: c
Explanation: Teflon (CF 2 =CF 2 ) is a non-absorbent gasket. It is used in the industrial application to minimize the crevice corrosion. Whereas polyethylene and isoprene is absorbent to fluids such as water and acids.
7. Which of the following is also known as under film corrosion?
a) Crevice corrosion
b) Filiform corrosion
c) Galvanic corrosion
d) Pitting corrosion
Answer: b
Explanation: Filiform corrosion is a special type of crevice corrosion. It is also known as under film corrosion as it occurred under protective coatings or films. It usually seen on food and beverage cans.
8. Which of the following is/are the effects of filiform corrosion?
a) Weakens the metal
b) Decreases tensile strength
c) Affects surface appearance
d) Weakens the metal, decreases tensile strength and affects the surface appearance
Answer: c
Explanation: This filiform corrosion affects only surface appearance on metal-coated food and beverage cans that are exposed to the high humid atmosphere. It doesn’t weaken the metal as well as decreases the tensile strength.
9. Which of the following industry has major concern on filiform corrosion?
a) Petroleum industry
b) Canning industry
c) Automobile industry
d) Petroleum and automobile industry
Answer: b
Explanation: The Canning industry has a major concern on filiform corrosion. As canning is a preservation method by sealing the container’s airtightly and applying epoxy coating on the metal surface. Whereas the petroleum and automobile industry face uniform and galvanic corrosion as a major concern.
10. Which of the following ion/ions that result in the blue-green color of the active head in a corrosion filament?
a) Ferrous ions
b) Ferric oxide ions
c) Hydrated ferric oxide ions
d) Ferric oxide and hydrated ferric oxide ions
Answer: a
Explanation: A under film corrosion filament consists of an active head and inactive tail. The active head contains ferrous ions, that have a characteristic color of blue-green. Whereas inactive tail contains ferric oxide and hydrated ferric oxide ions, that has a characteristic color of red-brown.
11. Which of the following type of corrosion filament interaction is depicted in the given figure?
a) Reflection of corrosion filament
b) Splitting of corrosion filament
c) Joining of corrosion filament
d) Death trap of corrosion filament
Answer: d
Explanation: Since the growing filaments can’t cross inactive tails, they frequently get trapped and dies as the available space is decreased. This is known as the death trap.
12. Which of the following is the most environmental factor of filiform corrosion?
a) Relative humidity of the atmosphere
b) Temperature
c) pH of the environment
d) Temperature and pH of the environment
Answer: a
Explanation: Relative humidity of the surroundings is the most environmental factor of filiform corrosion. It occurs primarily between 65% to 90% relative humidity. If the relative humidity is less than 65%, the metal is unaffected.
13. What are the preventions of filiform corrosion?
a) Use of coatings with low water permeability
b) To store in low-humidity environment
c) To store in high-humidity environment
d) Use of coatings with low water permeability and to store in a low-humidity environment
Answer: d
Explanation: Filiform corrosion is a special type of crevice corrosion, occurs under metal coatings in a relatively high-humidity environment
Preventions to filiform corrosion:
i. Use of coatings with low water permeability
ii. To store in a low-humidity environment
iii. Use of brittle films or coatings
14. Which of the following type of corrosion is depicted in the given figure?
a) Crevice corrosion
b) Galvanic corrosion
c) Filiform corrosion
d) Uniform corrosion
Answer: c
Explanation: Here, the figure depicts the corrosion of steel under film or coating. This corrosion is called filiform corrosion and it is caused due to the relative humidity of the atmosphere.
This set of Corrosion Engineering Multiple Choice Questions & Answers focuses on “Eight Forms – Pitting Corrosion”.
1. Pitting is a form of extremely localized attack that results in holes in the metal.
a) True
b) False
Answer: a
Explanation: Pitting and crevice corrosion are the localized corrosion types, that results in the corrosion on very confined corrosive sites. Localized attack of pitting results in holes in the metal.
2. Which of the following is the characteristic of a pit?
a) Cavity with the surface diameter about the less than the depth
b) Cavity with the surface diameter about the same as or less than the depth
c) Cavity with the surface diameter about the same as or high than the depth
d) Cavity with the surface diameter about the high than the depth
Answer: b
Explanation: Pitting is extremely localized corrosion that results in pits or cavity. A pit is a cavity with the surface diameter about the same as or less than the depth.
3. Which of the following form of corrosion is more destructive and insidious in nature?
a) Uniform corrosion
b) Intergranular corrosion
c) Pitting corrosion
d) Galvanic corrosion
Answer: c
Explanation: Pitting is one of the most destructive and insidious forms of corrosion. It causes equipment to fail because of perforation with only a small percent weight loss of the entire structure.
4. Which of the following are the reasons that make it difficult to detect pits?
a) Small size
b) Varying depths
c) Pits covered with corrosion products
d) Small size, varying depths and covered with corrosion products
Answer: d
Explanation: It is difficult to measure the pitting quantitatively because of its small size, varying depth, and due to covered corrosion products. It fails the equipment because of perforation over the entire surface with only a small percent weight loss.
5. Which of the following metal is highly prone to pitting corrosion?
a) 18-8 stainless steel by sulfuric acid with FeCl 3
b) Titanium by sulfuric acid with FeCl 3
c) Nickel by sulfuric acid with FeCl 3
d) Copper by sulfuric acid with FeCl 3
Answer: a
Explanation: Pitting is one of the most destructive and insidious forms of corrosion. 18-8 stainless steel is highly prone to pitting corrosion by sulfuric acid in the presence of FeCl 3 . Whereas other metals are relatively resistant to pitting. Because it mainly depends on oxide film for its corrosion-resistant.
6. What is the usual direction for the growth of pits?
a) Vertically downwards
b) Vertically upwards
c) Horizontally sideward
d) Any primary direction
Answer: a
Explanation: Pits usually grow in the direction of gravity i.e. vertically downwards. Gravitational force holds the corrosive solution vertically downwards in a cavity, that makes the pit growth downwards. And very a smaller number of pits grown vertically upwards.
7. Pitting usually requires an incubation period ranges from months to years.
a) False
b) True
Answer: b
Explanation: Pitting can occur in two steps: i. Pit initiation ii. Pit growth.
The incubation period is the time required for a system to initiate pits on the metal surface. It usually ranges from months to years.
8. Which of the following corrosion form is depicted in the given figure?
a) Crevice corrosion
b) Uniform corrosion
c) Intergranular corrosion
d) Pitting corrosion
Answer: d
Explanation: Here, pitting corrosion is depicted in the figure. Pitting is extremely localized corrosion that results in pits or cavity and it is the most destructive and insidious form of corrosion.
9. Which of the following corrosion form is considered as the intermediate stage between uniform corrosion and complete corrosion resistance?
a) Galvanic corrosion
b) Pitting corrosion
c) Intergranular corrosion
d) Erosion corrosion
Answer: b
Explanation:
Case A: No corrosion of metal
Case B: Intense pitting on specific points
Case C: Uniform corrosion
10. Which of the following corrosion form is/are autocatalytic in nature?
a) Pitting and crevice corrosion
b) Crevice corrosion only
c) Pitting corrosion only
d) Pitting and intergranular corrosion
Answer: a
Explanation: Autocatalytic is a phenomenon of rapid corrosion that occurs within the pit or crevice, while oxygen reduction takes place on adjacent surfaces. This process is self-stimulating and self-propagating. It occurs in both pitting and crevice corrosion.
11. Which of the following statement is correct regarding pitting corrosion?
a) Adjacent surfaces cathodically protect pits
b) Pits cathodically protect adjacent surfaces
c) Neither pits nor adjacent surfaces protect each other
d) Both pits and adjacent surfaces protect each other
Answer: b
Explanation: Pits cathodically protect adjacent surfaces of metal; this is also called as cathodic protection. This is due to the autocatalytic nature of pitting corrosion. Hence, pits cathodically protect adjacent surfaces is the correct statement.
12. Which of the following is/are the difference between the crevice and pitting corrosion?
a) Autocatalytic nature
b) Corrosion mechanism
c) Initiation method
d) Both the corrosion mechanism and initiation method
Answer: c
Explanation: Pitting is a special case of crevice corrosion. But in the view of the initiation method, these two-corrosion processes are different. Pitting corrosion is a self-initiating corrosion form, whereas crevice corrosion needs the formation of crevice with differential concentration from outside.
13. Which of the following ions have a high tendency to pitting corrosion?
a) Chlorides
b) Bromides
c) Hypo chlorites
d) Chlorides, bromides, and hypochlorites
Answer: d
Explanation: In practical applications, most pitting failures are caused by chloride ions, hypochlorites, and bromide ions. Oxidizing metal ions with chlorides are aggressive pitters. Cupric, ferric, and mercuric halides are extremely aggressive.
14. Which of the following ions, that can reduce pitting corrosion?
a) Hydroxide salts
b) Chromate salts
c) Silicate salts
d) Hydroxide, chromate and silicate salts
Answer: d
Explanation: Pitting is one of the most destructive and insidious forms of corrosion. The tendency of pitting can be increased with the presence of chloride, bromide, and hypochlorites. But this tendency can be prevented or minimized with the presence of hydroxide, chromate, and silicate salts.
15. Which of the following corrosion test is most reliable to know the extent of pitting corrosion?
a) To measure the average depth of pits
b) To measure the maximum depth of a pit
c) Weight loss method
d) Weight gain method
Answer: b
Explanation: The measurement of maximum depth of pit would be a more reliable way of expressing pitting corrosion. As metal loss or metal gain is very small and does not indicate the depth of penetration.
This set of Corrosion Engineering Multiple Choice Questions & Answers focuses on “Eight Forms – Intergranular Corrosion – 1”.
1. Which of the following is/are more reactive in intergranular corrosion?
a) Grain
b) Grain boundary
c) Both grain and grain boundary
d) Neither grain nor grain boundary
Answer: b
Explanation: Intergranular corrosion occurs when grain interfaces or grain boundaries are very reactive than the face of grain. Whereas in the uniform attack, grains are more reactive than the grain boundaries.
2. What is Intergranular corrosion?
a) Localized attack at the grain boundaries
b) Localized attack at the grain faces
c) Uniform attack on grains
d) Localized attack at and adjacent to the grain boundaries
Answer: d
Explanation: Intergranular corrosion means corrosion in between two or more grains. Intergranular corrosion is a localized attack at and adjacent to the grain boundaries.
3. Which of the following is/are the causes of intergranular corrosion?
a) Impurities at the grain boundaries
b) Enrichment of one of the alloying elements at the grain boundary
c) Depletion of one of the alloying elements at the grain boundary
d) Impurities at the grain boundaries, enrichment, and depletion of one of the alloying elements at the grain boundary
Answer: d
Explanation: Intergranular corrosion is the corrosion occurs between two or more grains. It causes due to the presence of a differential concentration of alloying elements at the grains and grain boundaries. And the causes for this are as follows I. Presence of impurities at the grain boundaries
II. Enrichment of one of the alloying elements
III. Depletion of one of the alloying elements
4. Which of the following alloys is/are prone to intergranular corrosion?
a) Iron in aluminum
b) Zinc in brass
c) 18-8 Stainless steel
d) Iron in aluminum, zinc in brass and 18-8 stainless steel
Answer: d
Explanation: All the given alloys are prone to intergranular corrosion. Iron in aluminum and zinc in brass are susceptible to this corrosion, due to the segregation of iron and zinc respectively at the grain boundaries. Whereas 18-8 Stainless steel is susceptible due to the depletion of chromium at the grain boundaries.
5. Numerous failures of 18-8 Stainless steel have occurred in the temperature range of 950 to 1450°F
a) True
b) False
Answer: a
Explanation: Numerous failures of 18-8 stainless steel have occurred in the temperature range of 950 to 1450°F. When these steels are heated in the range of 950 to 1450°F they become sensitized or susceptible to intergranular corrosion due to the depletion of chromium at the grain boundary.
6. What is the molecular formula of chromium carbide formed due to the depletion of chromium in 18-8 stainless steel?
a) Cr 3 C
b) Cr 5 C 3
c) CrC
d) Cr 23 C 6
Answer: d
Explanation: Intergranular corrosion in 18-8 stainless steel is due to the depletion of chromium content at the grain boundary. This results in the formation of chromium carbide (Cr 23 C 6 ) at the grain boundary. Chromium depleted zone is highly prone to corrosion and it is known as intergranular corrosion.
7. Which of the following areas is/are corroded in the intergranular corrosion of stainless steel?
a) Grain only
b) Grain boundary only
c) Chromium depleted zone near the grain boundary
d) Both grain and grain boundary
Answer: c
Explanation: !8-8 stainless steel is susceptible to intergranular corrosion due to sensitization in the temperature of 950 to 1450°F. At this stage, chromium reacts with carbon near the grain boundary and results in the formation of the chromium depleted zone. This chromium depleted zone is prone to intergranular corrosion.
8. What is the minimum percent of chromium is needed to make stainless steel?
a) 2%
b) 20%
c) 1%
d) 11%
Answer: d
Explanation: Stainless steel is a family of iron-based alloys that contain a minimum of 11% chromium. Chromium imparts corrosive resistance to steel. There are 4 types of stainless steel.
They are i. Austenitic stainless steels
ii. Martensitic stainless steels
iii. Ferritic stainless steels
iv. Duplex stainless steels
9. Which of the following characteristics of the impoverished area, results in a rapid corrosion attack?
a) Less corrosion resistance
b) The high content of chromium
c) The large unfavorable area ratio
d) Less corrosion resistance and large unfavorable area ratio
Answer: d
Explanation: Rapid corrosion attack in impoverished or chromium depleted zone is due to
i. Less corrosion resistance
ii. Two dissimilar metal compositions are in contact
iii. Large unfavorable area ratio is present
10. Which of the following corrosion type is depicted in the given figure?
a) Intergranular corrosion
b) Galvanic corrosion
c) Crevice corrosion
d) Pitting corrosion
Answer: a
Explanation: Intergranular corrosion is the corrosion occurs between two or more grains. It causes due to the presence of a differential concentration of alloying elements at the grains and grain boundaries. Stainless steels are highly prone to this intergranular corrosion.
11. What is the structure of chromium carbide that precipitates at the grain boundaries?
a) Acicular structure
b) Leaflike structure
c) Lamellar structure
d) No specific structure
Answer: b
Explanation: Mahla and Nielsen of Du Pont, using the electron microscope, have shown that the carbides form on the envelope around the grains in a leaflike structure.
12. Which of the following term is associated with intergranular corrosion in welded structures?
a) Intergranular weld
b) Weld failure
c) Weld decay
d) Weld corrosion
Answer: c
Explanation: The intergranular corrosion associated with the welded structures and metals is known as weld decay. The depletion of alloying takes place adjacent to the weld bead as it exposed to high temperature .
13. Which of the following is used to visualize the heat flow and temperatures during welding?
a) Weld decay
b) Intergranular corrosion
c) Tablecloth analogy
d) Weld decay and intergranular corrosion
Answer: c
Explanation: Tablecloth analogy of heat flow and temperatures is used during welding. To visualize a mountain like a block with the rise and fall of each stripe represents the rise and fall of temperature in a welded plate.
14. Electric arc welding is used more than the gas welding for stainless steel to reduces the chances of weld decay.
a) True
b) False
Answer: a
Explanation: Welding time and the peak temperature of welding are the two parameters of weld decay. Electric arc welding produces more intense heat in a shorter time whereas in gas welding it is less intense and requires more time for welding.
15. Which of the following corrosives that induce intergranular corrosion in austenitic stainless steel?
a) Acetic acid
b) Acetic acid+salicylic acid
c) Ammonium nitrate
d) Acetic acid, acetic acid+salicylic acid, ammonium nitrate
Answer: d
Explanation: Stainless steel is highly susceptible to intergranular corrosion. These corrosives such as acetic acid, acetic acid+salicylic acid, ammonium nitrate, etc. Induces the intergranular corrosion in austenitic stainless steel.
This set of Corrosion Engineering Quiz focuses on “Eight Forms – Intergranular Corrosion – 2”.
1. Which of the following is/are the methods to control intergranular corrosion of austenitic stainless steel?
a) Employing solution-quenching
b) Adding stabilizers
c) Lowering the carbon content to below 0.03%
d) Employing solution-quenching, adding stabilizers and lowering the carbon content to below 0.03%
Answer: d
Explanation: Austenitic stainless steels are highly prone to intergranular corrosion. It can be minimized by
i. Employing quench-annealing or solution-quenching
ii. Adding stabilizers that forms strong carbides
iii. Lowering the carbon content to below 0.03%
2. Which of the following temperature range is required for commercial solution-quenching treatment?
a) 200°F-500°F
b) 800°F-1200°F
c) 1300°F-1700°F
d) 1950°F-2050°F
Answer: d
Explanation: Commerical solution-quenching treatment consists of heating to 1950°F to 2050°F followed by water quenching. Chromium carbide is dissolved at these temperatures, and a more homogenous alloy is formed. It minimizes the susceptibility of weld metal to weld decay.
3. Which of the following is/are the stabilizing elements to minimize intergranular corrosion of stainless steel?
a) Niobium
b) Columbium
c) Titanium
d) Niobium, columbium, and titanium
Answer: d
Explanation: Stabilizing elements are the elements that form strong carbides than chromium. These elements have a much greater affinity to carbon than does chromium, this minimizes the chromium depleted zone.
4. Which of the following region is indicated as BC in the given figure?
a) Weld bead
b) Heat affected zone
c) Weld decay
d) Neither weld decay nor bead
Answer: c
Explanation: Here in the given figure, region BC represents the weld decay zone and it is exposed to sensitizing temperature range during welding. This weld decay zone is highly susceptible to intergranular corrosion.
5. Carbon pickup during the production of austenitic stainless steels has caused premature failures of intergranular corrosion.
a) True
b) False
Answer: a
Explanation: Carbon pickup or surface carburization during the production of austenitic stainless steel has caused premature failures. It occurs when these steels are cast into molds that contain carbonaceous materials such as organic binders and baked oil sand. It reduces the corrosive resistance of these steels in the viewpoint of intergranular attack.
6. The intergranular attack is evident in the resin shell casting but not on the ceramic mold casting.
a) True
b) False
Answer: a
Explanation: Intergranular attack is evident in the resin shell casting but not on the ceramic mold casting. It is because of organic binders or organic content used for mold making in resin shell casting. It increases the surface carbon content of casting by the phenomenon known as carbon pickup.
7. What is the abbreviation of KLA regarding intergranular corrosion?
a) Knife-Line Attack
b) Knight-Line Attack
c) Knife-Life Action
d) Knight-Life Action
Answer: a
Explanation: KLA is abbreviated as Knife-Line Attack. Knife-Line Attack is similar to weld decay in that they both results from intergranular corrosion and both are associated with welding.
8. Which of the following is/are the characteristics of the Knife-line attack?
a) KLA occurs immediately adjacent to the weld
b) KLA occurs in the stabilized steels only
c) KLA occurs in the non-stabilized steels only
d) KLA occurs in the stabilized steels and it occurs immediately adjacent to the weld
Answer: d
Explanation: KLA occurs in a narrow band in the parent metal adjacent to weld and it occurs in the stabilized steels that are alloyed with niobium, titanium, and columbium.
9. Which of the following is the best remedy for the Knife-Line attack?
a) Heating the welded stabilized steel in the range of 950°F to 1400°F
b) Heating the welded stabilized steel in the range of 1400°F to 1900°F
c) Heating the welded stabilized steel to 1950°F
d) Heating the welded stabilized steel in the range of 1950°F to 2500°F
Answer: c
Explanation: The temperature range of 950°F to 1400°F is the sensitizing zone where only chromium carbide precipitates. Heating the welded stabilized steel to 1950 0 F results in the dissolution of chromium carbide and precipitation of columbium carbide.
10. Which of the following alloys exhibits intergranular corrosion by steam and marine atmospheres?
a) Die-cast zinc alloy
b) Duralumin alloy
c) Both die-cast zinc alloy and duralumin alloy
d) Neither die-cast zinc alloy nor duralumin alloy
Answer: a
Explanation: Die-cast zinc alloys containing aluminum exhibit intergranular corrosion by steam and marine atmosphere. Whereas duralumin alloys are also susceptible to intergranular corrosion in a different atmosphere.
This set of Corrosion Engineering Multiple Choice Questions & Answers focuses on “Eight Forms – Selective Leaching”.
1. Selective Leaching is the removal of one element from a solid alloy by the corrosion process.
a) True
b) False
Answer: a
Explanation: Selective leaching is one of the types of corrosion that results in the removal of one element from a solid alloy by the corrosion process. Dezincification, dealuminumification, and decobaltification are examples of selective leaching.
2. What is the percent of zinc that consists of common yellow brass?
a) 70%
b) 30%
c) 40%
d) 60%
Answer: b
Explanation: The composition of common yellow brass is approximately 30% zinc and 70% copper. Dezincification alloy assumes a red or copper color that contracts to the original yellow color.
3. Which of the following is/are the types of dezincification?
a) Layer-type
b) Plug-type
c) Layer-type and Plug-type
d) Neither Layer-type nor Plug-type
Answer: c
Explanation: There are two common types of dezincification types. They are
i. Layer-type or uniform
ii. Plug-type or localized
4. The Alloying of zinc to copper lowers the corrosion resistance of the copper.
a) True
b) False
Answer: a
Explanation: Alloying of zinc to copper lowers the corrosion resistance of the copper. The oxide film of copper is highly dense, stable, and has a high resistance to corrosion. Whereas zinc-copper alloy has a relatively less stable oxide film.
5. Which of the following is/are the characteristics of dezincified brass alloy?
a) Weak
b) Permeable
c) Porous
d) Weak, permeable and porous
Answer: d
Explanation: Dezincified brass alloy is an alloy in which the zinc is removed in a particular corrosive solution by selective leaching. Weak, permeable, and porous are the characteristics of dezincified brass alloy.
6. Which of the following type of brasses is/are highly prone to the uniform or layer-type dezincification?
a) Low brasses
b) High brasses
c) Low and high brasses
d) Neither high nor low brasses
Answer: b
Explanation: The composition of high brasses is usually 65% copper and 35% zinc. High brasses are highly prone to the uniform or layer-type dezincification in acidic environments.
7. Which of the following type of brasses is/are highly prone to localize or plug-type dezincification?
a) Low brasses
b) High brasses
c) Low and high brasses
d) Neither low nor high brasses
Answer: a
Explanation: The composition of low brasses are usually 80% copper and 20% zinc. Low brasses are highly prone to localize or plug-type dezincification in alkaline, neutral, and slightly acidic environments.
8. Which of the following is/are the preventions of dezincification?
a) Minimizing oxygen concentration
b) Use of less susceptible alloy
c) Adding a small amount of arsenic, antimony
d) Removal of oxygen concentration, use of less susceptible alloy and adding a small amount of arsenic, antimony
Answer: d
Explanation: Dezincification can be minimized or reduced by
i. Minimizing the oxygen concentration in the environment
ii. Use of less susceptible alloy such as red brass
iii. Adding small amounts of arsenic, antimony, and phosphorus as an inhibitor
9. Which of the following phenomenon that results in the dissolution of iron by leaving porous graphite on the surface of grey cast iron?
a) Dezincification
b) Decalcification
c) Graphitization
d) Dezincification and graphitization
Answer: c
Explanation: Graphite is cathodic to iron in grey cast iron that results in the dissolution of iron by leaving porous graphite in a mild corrosive solution. This phenomenon is known as graphitization.
10. Which of the following type of cast irons that exhibits graphitization?
a) Grey cast iron
b) Nodular cast iron
c) Malleable cast iron
d) Grey cast iron, nodular cast iron, and malleable cast iron
Answer: a
Explanation: Graphitization occurs only in grey cast iron whereas it doesn’t occur in nodular, malleable, and white cast iron as the graphite network is not present to hold together at the surface.
11. Which of the following acid that results in selective removal of aluminum in aluminum bronzes?
a) Hydrochloric acid
b) Hydrofluoric acid
c) Nitric acid (HNO 3 )
d) Hydrochloric, hydrofluoric and nitric acid
Answer: b
Explanation: Selective Leaching is the removal of one element from a solid alloy by the corrosion process. And selective removal of aluminum from aluminum bronzes can be resulted by using hydrofluoric acid.
12. Which of the following is/are the other names of selective leaching?
a) Dealloying
b) Parting
c) Dealloying and parting
d) Neither dealloying nor parting
Answer: c
Explanation: Selective Leaching is the removal of one element from a solid alloy by the corrosion process. The other names of selective leaching are dealloying and parting.
13. Which of the following is/are the benefits of selective leaching?
a) Enrichment of silicon on stainless steel for better passivity
b) Preparation of Raney nickel catalyst
c) Extraction of metals using hydrometallurgy
d) Enrichment of silicon on stainless steel for better passivity, preparation of Raney nickel catalyst and extraction of metals using hydrometallurgy
Answer: d
Explanation: The benefits associated with selective leaching are
i. Enrichment of silicon on Stainless steel for better passivity
ii. Preparation of Raney nickel catalyst
iii. Extraction of metals using hydrometallurgy
14. Which of the following type of corrosion is depicted in the given figure?
a) Galvanic corrosion
b) Uniform corrosion
c) Selective leaching
d) Erosion corrosion
Answer: c
Explanation: Selective Leaching is the removal of one element from a solid alloy by the corrosion process. And in selective leaching, it is a layer or uniform type of zincification. It highly occurs in high brasses that contain 35% zinc approximately.
This set of Corrosion Engineering Multiple Choice Questions & Answers focuses on “Eight Forms – Erosion Corrosion”.
1. Erosion corrosion accelerates the rate of attack on a metal because of relative movement between corrosive fluid and the metal surface.
a) True
b) False
Answer: a
Explanation: Erosion corrosion is one of the types of corrosion that accelerates the rate of deterioration or attack on a metal because of the relative movement of corrosive fluid and the metal surface.
2. Which of the following type of directional patterns usually exhibit by erosion-corrosion?
a) Grooves
b) Waves
c) Rounded holes
d) Grooves, waves and rounded holes
Answer: d
Explanation: Erosion corrosion results in wear or abrasion of the surface of the metal. It is characterized in appearance by grooves, gullies, waves, rounded holes, and valleys.
3. Which of the following type of corrosion is depicted in the given figure?
a) Uniform corrosion
b) Erosion corrosion
c) Galvanic corrosion
d) Selective leaching
Answer: b
Explanation: Erosion corrosion is depicted in the given figure. Erosion corrosion accelerates the rate of deterioration or attack on a metal because of the relative movement of corrosive fluid and the metal surface.
4. Erosion corrosion results when the protective oxide films are damaged and the metal or alloy are attacked at a rapid rate.
a) True
b) False
Answer: a
Explanation: As the relative movement of the corrosive solution and the surface of the metal increases the intensity of erosion-corrosion increases. At higher velocities, it results in the damage or worn out of oxide film and it attacks the metal rapidly.
5. Which of the following metals is/are susceptible to erosion-corrosion?
a) Aluminum
b) Lead
c) Stainless steel
d) Aluminum, lead and stainless steel
Answer: d
Explanation: Aluminum, lead, copper, and stainless steel are the metals that are susceptible to erosion-corrosion. Because these metals mainly depend on their oxide film for its corrosive resistance.
6. Which of the following type of equipment is/are highly prone to erosion-corrosion?
a) In piping arrangements at elbows and bends
b) Measuring devices such as orifice and turbine blades
c) In piping arrangements at straight lines
d) In piping arrangements at elbows and bends and measuring devices such as orifice and turbine blades
Answer: d
Explanation: Erosion corrosion can be affected by the relative velocity of the corrosive solution and metal surface and along with impingement velocity at the edges and turnings. In piping arrangements at elbows and bends and measuring devices such as orifice and turbine blades are the equipment that is prone to erosion-corrosion.
7. Which of the following is/are the characteristics of oxide film that exhibits better resistance to erosion-corrosion?
a) Hard
b) Dense
c) Adherent
d) Hard, dense and adherent
Answer: d
Explanation: Erosion corrosion is the type of corrosion that results in mechanical damage of the metal due to the high velocities of corrosive solutions. And a hard, dense, and adherent oxide film can exhibit better resistance to erosion-corrosion.
8. Which of the following characteristics of titanium, makes it resistant to erosion-corrosion?
a) Stability of titanium oxide
b) Instability of titanium oxide
c) The low reactivity of titanium
d) The low reactivity of titanium and instability of titanium oxide
Answer: a
Explanation: Titanium is a reactive metal but is resistant to erosion-corrosion in many environments because of the stability of the titanium oxide (TiO 2 ) film. It reforms its oxide layer within a fraction of seconds after wearing out.
9. Which of the following metal is resistant to seawater, chlorides, and fuming nitric acid?
a) Aluminum
b) Lead
c) Titanium
d) Stainless steel
Answer: d
Explanation: Titanium is highly resistant to seawater, chlorides, and fuming nitric acid. It is also resistant to erosion-corrosion because of its high reactivity and stability of oxide film.
10. Which of the following environmental factor plays an important role in erosion-corrosion?
a) Velocity
b) Corrosive concentration
c) pH of the environment
d) Relative humidity of the atmosphere
Answer: a
Explanation: Erosion corrosion accelerates the rate of attack on a metal because of relative movement between corrosive fluid and the metal surface. It increases as the velocity of the corrosive solution increases.
11. Define critical velocity regarding erosion-corrosion.
a) Velocity at which erosion-corrosion starts
b) Velocity at which erosion-corrosion stops
c) Velocity after which erosion-corrosion increases exponentially
d) Velocity after which erosion-corrosion decreases exponentially
Answer: c
Explanation: Critical velocity is the velocity after which the erosion-corrosion increases exponentially. Case 1 :
Erosion corrosion increases linearly with increase with velocity.
Case 2 :
Erosion corrosion increases exponentially with increase with velocity.
12. Which of the following metal shows a decrease in corrosion attack with an increase in velocity in fuming nitric acid?
a) Aluminum
b) Carbon steel
c) Stainless steel 347
d) Copper
Answer: c
Explanation: Under stagnant conditions, stainless steel 347 in nitric acid is attacked autocatalytically because of the formation of nitrous acid as a cathodic reaction product. An increase in velocity sweeps away the corrosive nitrous acid in the environment.
13. Which of the following is/are the preventions of erosion-corrosion?
a) Selection of better resistant materials
b) Alteration of the environment
c) Applying protective coatings
d) Selection of better resistant materials, alteration of the environment and applying protective coatings
Answer: d
Explanation: Methods for minimizing or preventing erosion-corrosion
i. Selection of better resistant materials
ii. Design of equipment
iii. Alteration of environment
iv. Applying protective coatings
v. Cathodic protection of equipment.
14. Which of the following is/are the aspects of design to minimize erosion-corrosion?
a) Increasing pipe diameter
b) Avoiding sharp edges and turnings
c) Readily replaceable impingement plates should be inserted
d) Increasing pipe diameter, avoiding sharp edges and turnings and readily replaceable impingement plates should be inserted
Answer: d
Explanation: Design is an important factor to minimize or combat erosion-corrosion. The design includes increasing pipe diameter, avoiding sharp edges and turnings, readily replaceable impingement plates should be inserted, and maintaining certain angles to minimize impingement area.
15. Which of the following is/are the aspects of alteration of the environment to minimize erosion-corrosion?
a) Deaeration of corrosive solution
b) Decrease the temperature
c) Use of Settling and filtration to remove suspended solids
d) Deaeration of the corrosive solution, decrease the temperature and use of settling and filtration to remove suspended solids
Answer: d
Explanation: Alteration of the environment is also one of the methods to minimize erosion-corrosion. This includes the deaeration of corrosive solution, decrease the temperature and use of settling and filtration to remove suspended solids.
This set of Corrosion Engineering MCQs focuses on “Eight Forms – Cavitation and Fretting Corrosion”.
1. Which of the following type of corrosion is caused by the formation and collapse of vapor bubbles in a liquid near the metal surface?
a) Filiform corrosion
b) Fretting corrosion
c) Cavitation damage
d) Crevice corrosion
Answer: c
Explanation: Cavitation damage is the special form of erosion-corrosion that occurs by the formation and collapse of vapor bubbles in a liquid near a metal surface.
2. Which of the following equipment encounters cavitation damage in the service?
a) Hydraulic turbines
b) Ship propellers
c) Pump impellers
d) Hydraulic turbines, ship propellers, and pump impellers
Answer: d
Explanation: Cavitation damage occurs in hydraulic turbines, ship propellers, pump impellers, and other surfaces where high-velocity liquid flow and pressure changes are encountered.
3. Which of the following condition is/are correct regarding the boiling point of a liquid with an increase in pressure?
a) Decreases up to triple point
b) Increases up to triple point
c) Increases up to the critical point
d) Decreases up to the critical point
Answer: a
Explanation: As the pressure of a liquid decreases, its boiling point decreases up to its triple point. As the pressure increases its increases up to a critical point.
Example: At higher altitudes boiling point of liquids reaches low as atmospheric pressure decreased.
4. Which of the following will result due to cavitation damage of a metal?
a) Mechanical action
b) Chemical dissolution
c) Both mechanical action and chemical dissolution
d) Neither mechanical action nor chemical dissolution
Answer: c
Explanation: Cavitation damage is the special form of erosion-corrosion that occurs by the formation and collapse of vapor bubbles in a liquid near a metal surface. It results in the mechanical and chemical dissolution of metal.
5. Cavitation damaged can be reduced by changing the design to minimize hydrodynamic pressure differences in process streamflow.
a) False
b) True
Answer: b
Explanation: Cavitation damaged can indeed be reduced by changing the design to minimize hydrodynamic pressure differences in process streamflow. It reduces the impingement area and force of the stream.
6. Which of the following type of corrosion is depicted in the given figure?
a) Fretting corrosion
b) Crevice corrosion
c) Cavitation damage
d) Pitting corrosion
Answer: c
Explanation: Cavitation damage is depicted in the given figure. It occurs by the formation and collapse of vapor bubbles in a liquid near a metal surface. And it results in mechanical action and chemical dissolution of metal.
7. Which of the following type of corrosion that occurs at contact areas between materials under load subjected to vibration or relative motion?
a) Fretting corrosion
b) Crevice corrosion
c) Cavitation damage
d) Pitting corrosion
Answer: a
Explanation: Fretting corrosion is the special type of erosion-corrosion that occurs at the contact areas between materials under load subjected to vibration or relative motion.
8. Which of the following is/are the other names of fretting corrosion?
a) Friction oxidation
b) Wear oxidation
c) False brinelling
d) Friction oxidation, wear oxidation and false brinelling
Answer: d
Explanation: Fretting corrosion is one of the special types of erosion-corrosion. It also called friction oxidation, wear oxidation, chafing, and false brinelling. Because it gets initiated with wear or friction and oxides debris are formed during corrosion.
9. Which of the following is/are the classic cases of fretting corrosion?
a) Bolted tie plates on railroad rails
b) Press-fitted ball bearing race on a shaft
c) On ball bearings
d) Bolted tie plates on railroad rails and press-fitted ball bearing race on a shaft
Answer: d
Explanation: Fretting corrosion occurs at contact areas between materials under load subjected to vibration or repeated relative motion. And it doesn’t occur on materials in continuous motion such as on ball bearings.
10. Which of the following is/are the basic requirements for the occurrence of fretting corrosion?
a) The interface must be under load
b) Vibration or repeated relative motion between the two surfaces
c) The interface must be under load and vibration or repeated relative motion between the two surfaces
d) The relative motion should be high
Answer: c
Explanation: The basic requirements for the occurrence of fretting corrosion are:
i. The interface must be under load
ii. Vibration or repeated relative motion between the two surfaces
iii. The load and the relative motion of the interface must be sufficient to produce deformation.
11. Which of the following is/are the preventive measures of fretting corrosion?
a) Lubricate with low-viscosity, high-tenacity oil
b) Increasing surface hardness by shot-peening or cold working
c) Use gaskets to absorb vibrations
d) Lubricate with low-viscosity, high-tenacity oil, increasing surface hardness by shot-peening and use gaskets to absorb vibrations
Answer: d
Explanation: Preventive measures to minimize fretting corrosion:
i. Lubricate with low-viscosity, high-tenacity oil, and greases
ii. Increasing surface hardness by shot-peening or cold working
iii. Use gaskets to absorb vibrations and exclude oxygen at bearing surfaces
iv. Increase the load to decrease slip between two metals.
This set of Corrosion Engineering Multiple Choice Questions & Answers focuses on “ Eight Forms – Stress Corrosion”.
1. What is the abbreviation of SCC regarding corrosion?
a) Stress-corrosion cracking
b) Stress-cracking corrosion
c) Stress-corrosion contact
d) Stress-contact corrosion
Answer: a
Explanation: SCC can be abbreviated as stress-cracking corrosion. It is referred to the simultaneous action of corrosion and stress on a metal structure. Tensile stress is the most common stress that encounters in the industrial world.
2. Stress-corrosion cracking occurs due to the simultaneous presence of tensile stress and a specific corrosive medium.
a) True
b) False
Answer: a
Explanation: Stress–corrosion cracking occurs due to the simultaneous presence of tensile stress either is caused by residual or external stress and a specific corrosive medium. Residual stress is caused due to welding, cold working, etc.
3. Which of the following is/are the classic examples of stress-corrosion cracking?
a) Season cracking of brass
b) Caustic embrittlement of steel
c) Season cracking of brass and caustic embrittlement of steel
d) Neither season cracking of brass nor caustic embrittlement of steel
Answer: c
Explanation: The two main classic examples of stress-corrosion cracking are:
i. Season cracking of brass
ii. Caustic embrittlement of steel.
4. What is meant by season cracking of brass?
a) Stress-corrosion cracking failure of brass cat ridge cases due to ammonia
b) Stress-corrosion cracking failure of brass cat ridge cases due to caustic soda
c) Stress-corrosion cracking failure of brass cat ridge cases due to caustic soda and ammonia
d) Stress-corrosion cracking failure with brittle fracture
Answer: a
Explanation: Season cracking refers to the stress-corrosion cracking failure of brass cat ridge cases. The main important environmental component in season cracking is ammonia, which results from the decomposition of organic matter.
5. What is meant by caustic embrittlement of steel?
a) Failure of cold-worked rivets by a brittle fracture in the presence of ammonia
b) Failure of cold-worked rivets by a brittle fracture in the presence of caustic soda
c) Failure of cold-worked rivets by a brittle fracture in the presence of caustic soda and ammonia
d) Failure of cold-worked rivets by the cup and cone fracture in the presence of caustic soda
Answer: b
Explanation: Explosions of riveted boilers that occurred in early steam-driven locomotives are due to the cold working during the operation. Hence, brittle fracture in the presence of caustic resulted in caustic embrittlement.
6. In which of the following environments that stainless steel will undergo stress-corrosion cracking?
a) Chlorides
b) Caustics
c) Ammonia
d) Chlorides and caustics
Answer: d
Explanation: Stainless steel undergoes stress-corrosion cracking in chlorides and caustics. They do not crack in ammonia, sulfuric acid, nitric acid, acetic acid, and pure water.
7. Which of the following is/are the most important variables that affect stress-corrosion cracking?
a) Temperature
b) Metal composition
c) Type and amount of stress applied
d) Temperature, metal composition, and type and amount of stress applied
Answer: d
Explanation: The most important variables that affect stress-corrosion cracking are:
i. Temperature
ii. Metal composition
iii. Corrosive solution composition
iv. Type and amount of stress applied
v. Design of metal structure.
8. Which of the following alloy in which both intergranular and trans-granular cracking occurs?
a) High-nickel alloys
b) iron-chromium alloys
c) Brasses
d) High-nickel alloys, iron-chromium alloys, and brasses
Answer: d
Explanation: Stress-corrosion cracking can be intergranular and trans-granular cracking. Alloys such as high-nickel alloys, iron-chromium alloys, and brasses often crack both in intergranular and transgranular manner.
9. Define Threshold stress regarding stress-corrosion cracking.
a) The maximum stress at which the specimen ruptures
b) The maximum stress required to prevent cracking
c) The minimum stress required to prevent cracking
d) The minimum stress at which cracking starts
Answer: c
Explanation: Increasing stress decreases the time before cracking occurs. Threshold stress is the minimum stress required to prevent cracking. It depends on temperature, alloy composition, and environment composition.
10. As stress-corrosion cracks penetrate the material, the cross-sectional area gets reduced under constant tensile load.
a) False
b) True
Answer: b
Explanation: Stress-corrosion cracking is the simultaneous attack of corrosion and stress. A stress-corrosion crack penetrates the material; the cross-sectional area gets reduced under constant tensile stress.
11. Which of the following is/are the environments that cause stress-corrosion cracking to titanium?
a) Red fuming nitric acid
b) Methanol-HCl
c) Nitrogen tetroxide (N 2 O 4 )
d) Red fuming nitric acid, methanol-HCl, and nitrogen tetroxide
Answer: d
Explanation: Stress-corrosion cracking is the simultaneous action of stress and corrosive environment on a metal. Red fuming nitric acid, methanol-HCl, and nitrogen tetroxide are the environments that may cause stress-cracking corrosion.
12. Which of the following is/are the metallurgical factors that affect stress-corrosion cracking?
a) Chemical composition
b) Distribution of precipitates
c) Dislocation interactions
d) Chemical composition, distribution of precipitates and dislocation interactions
Answer: d
Explanation: Metallurgical factors that affect stress-corrosion cracking are:
i. Average chemical composition
ii. Preferential orientation of grains
iii. Distribution of precipitates
iv. Dislocation interactions
v. Degree of metastability.
13. Which of the following type of stress has an important role in rupturing protective films during both the initiation and propagation of cracks?
a) Tensile stress
b) Compressive stress
c) Shear stress
d) Compressive and shear stress
Answer: a
Explanation: Tensile stress has an important role in rupturing protective films during both the initiation and propagation of cracks. Breaks in the passive layer of metal induce a rapid attack.
14. Which of the following stress-corrosion cracking mechanism is highly acceptable?
a) Dissolution mechanics
b) Mechanical mechanics
c) Both dissolution and mechanical mechanics
d) Hydrogen mechanics
Answer: a
Explanation: Dissolution mechanics is highly acceptable than mechanical mechanics. The dissolution model describes anodic dissolution at the crack tip, as strain ruptures the passive film at the tip.
15. Which of the following is/are the preventions of stress-corrosion cracking?
a) Lowering working stress below the threshold value
b) Shot peening to produce residual compressive stresses
c) Applying for cathodic protection
d) Lowering working stress below the threshold value, shot peening to produce residual compressive stresses and applying for cathodic protection
Answer: d
Explanation: Methods to prevent stress-corrosion cracking are:
i. Lowering working stress below the threshold value
ii. Shot peening to produce residual compressive stresses
iii. Applying cathodic protection to the structure
iv. Adding inhibitors to the system
v. Eliminating the critical environment species.
This set of Corrosion Engineering Multiple Choice Questions & Answers focuses on “Eight Forms – Corrosion Fatigue”.
1. Corrosion fatigue is defined as the reduction of fatigue resistance due to the presence of a corrosive medium.
a) True
b) False
Answer: a
Explanation: Corrosion fatigue is a simultaneous action of corrosion and fatigue on a metal. It is defined as the reduction in fatigue resistance due to the presence of a corrosive medium.
2. What is meant by fatigue?
a) The tendency of a metal to fracture under static loading
b) The tendency of a metal to fracture under repeated cyclic loading
c) The tendency of a metal to fracture under non-repeating cyclic loading
d) The tendency of a metal to fracture after heavy deformation
Answer: b
Explanation: Fatigue is defined as the tendency of a metal to fracture under repeated cyclic loading. Bridges, machines will usually fail due to fatigue. It fails the metals even below the yield stress of that metal due to repeated cyclic loading.
3. What is the nature of fatigue fracture?
a) Brittle fracture
b) Cup and cone fracture
c) Tensile fracture
d) Brittle and tensile fracture
Answer: a
Explanation: A fatigue crack propagates until the cross-sectional area of the metal is reduced to the point where the ultimate strength is exceeded and rapid brittle fracture occurs. The nature of fatigue fracture is brittle.
4. Which of the following type of corrosion is depicted in the given figure?
a) Cavitation damage
b) Fretting corrosion
c) Corrosion fatigue
d) Uniform corrosion
Answer: c
Explanation: Corrosion fatigue is defined as the simultaneous effect of corrosion and fatigue on a metal. A fatigue crack propagates until the cross-sectional area of the metal is reduced to the point where the ultimate strength is exceeded and rapid brittle fracture occurs. And the other part experience corrosion.
5. Define the fatigue limit of a metal.
a) Stress below which metal will endure an infinite number of cycles without fracture
b) Stress above which metal will endure an infinite number of cycles without fracture
c) Stress at which metal will endure a less finite number of cycles
d) Stress at which metal will endure a more finite number of cycles
Answer: a
Explanation: Fatigue limit is the stress below which metal will endure an infinite number of cycles without fracture. The fatigue limit can be calculated by stress and the number of cycles curve.
6. Which of the following metal is depicted by curve A of given SN graph?
a) Aluminum
b) Tungsten
c) Steel
d) Calcium
Answer: a
Explanation: The given figure is an SN curve with the stress of the y-axis and the number of cycles on the x-axis. Curve A depicts the SN curve of nonferrous metals such as aluminum, copper, and nickel. Fatigue resistance for these metals increases with decreases in stress applied.
7. Which of the following metal is depicted in curve B of a given SN graph?
a) Aluminum
b) Copper
c) Steel
d) Zinc
Answer: c
Explanation: Ferrous alloys exhibit an increase in fatigue resistance with a decrease in stress, after that, it remains independent of stress applied. This point is known as the fatigue limit of the metal. It is defined as the stress below which the metal will endure an infinite number of cycles without fracture.
8. Which of the following is/are the factors that influence corrosion fatigue?
a) Type of metal
b) Composition of corrosive solution
c) Temperature
d) Type of metal, corrosive solution composition, and temperature
Answer: d
Explanation: The factors that influence corrosion fatigue:
• Type of metal
• Composition of corrosive solution
• Temperature
• PH of the environment
• Percentage of oxygen content.
9. Which of the following is/are the facts that indicate the reduction in fatigue resistance of metal?
a) Corrosion pits act as stress raisers
b) Corrosion pits act as initiate cracks
c) Corrosion pits act as a stress raiser and initiate cracks
d) Corrosion pits neither act as stress raiser nor initiate cracks
Answer: c
Explanation: Corrosion fatigue is the combination of both corrosion and fatigue simultaneously. Fatigue resistance is reduced because corrosion pits act as stress raisers and initiate cracks.
10. Which of the following is/are the preventions of corrosion fatigue?
a) Use of high tensile strength metals
b) Perform shot penning to induce compressive stresses
c) Use coatings such as electrodeposited zinc, nickel
d) Use of high tensile strength metals, perform shot penning to induce compressive stresses and use of coatings such as electrodeposited zinc, nickel
Answer: d
Explanation: Methods to prevent corrosion fatigue:
• Use of high tensile strength metals
• Perform shot penning to induce compressive stresses
• Use coatings such as electrodeposited zinc, nickel, chromium, copper and nitride coatings.
This set of Corrosion Engineering Multiple Choice Questions & Answers focuses on “Eight Forms – Hydrogen Damage”.
1. Hydrogen damage refers to the mechanical damage of a metal caused by the presence of or interaction of hydrogen.
a) True
b) False
Answer: a
Explanation: Hydrogen damage refers to the mechanical damage of a metal caused by the presence of or interaction of hydrogen. And hydrogen damage can be classified into four types based on the mechanism of failure.
2. Which of the following is/are the types of hydrogen damage?
a) Hydrogen blistering
b) Hydrogen embrittlement
c) Decarburization
d) Hydrogen blistering, hydrogen embrittlement, and decarburization
Answer: d
Explanation: Classification of hydrogen damage:
Hydrogen blistering
Hydrogen embrittlement
Decarburization
Hydrogen attack.
3. What is meant by hydrogen blistering?
a) Entrapment of hydrogen molecules in the metal voids
b) Formation of brittle metal hydrides
c) Entrapment of metal hydrides in the metal voids
d) Entrapment of hydrogen molecules and metal hydrides in the metal voids
Answer: a
Explanation: Hydrogen blistering refers to the local deformation of a metal due to the entrapment of hydrogen molecules in the metal voids. Initially, hydrogen atoms diffuse into metal and react with each other to form a hydrogen molecule.
4. What is meant by hydrogen embrittlement?
a) Entrapment of hydrogen molecules in the metal voids
b) Formation of brittle metal hydrides
c) Entrapment of metal hydrides in the metal voids
d) Entrapment of hydrogen molecules and metal hydrides in the metal voids
Answer: b
Explanation: Hydrogen embrittlement refers to the loss of ductility and strength of a metal due to the formation of brittle metal hydrides. Strong hydride forming metals such as titanium, results in brittle fracture.
5. Which of the following types of hydrogen damage processes are high-temperature processes?
a) Hydrogen blistering and hydrogen attack
b) Hydrogen attack and Decarburization
c) Decarburization and hydrogen embrittlement
d) Hydrogen attack only
Answer: b
Explanation: Hydrogen attack and decarburization are high-temperature processes. Decarburization refers to the removal of carbon from metal, is often produced by moist hydrogen at high temperatures. Hydrogen attack refers to the interaction of hydrogen and metal at high temperatures.
6. Which of the following industries has a major concern on hydrogen blistering?
a) Petroleum industry
b) Chemical manufacturing industries
c) Oil and natural gas refineries
d) Oil and natural gas refineries, petroleum and chemical manufacturing industries
Answer: d
Explanation: Hydrogen blistering refers to the local deformation of a metal due to the entrapment of hydrogen molecules in the metal voids.
Industries that have a major concern on hydrogen blistering are:
Petroleum industry
Chemical manufacturing industries
Oil and natural gas refineries
Welding workshops.
7. Which of the following type of compounds act as an inhibitor for hydrogen-ion reduction?
a) Sulfide ions
b) Phosphorous compounds
c) Arsenic compounds
d) Sulfide ions, phosphorous and arsenic compounds
Answer: d
Explanation: Hydrogen atoms diffuse into steel and other metals, which results in hydrogen blistering and hydrogen embrittlement. These inhibitors such as sulfide ions , phosphorous, and arsenic compounds reduce the rate of hydrogen-ion reduction.
8. Which of the following type of corrosion is depicted in the given figure?
a) Filiform corrosion
b) Hydrogen embrittlement
c) Hydrogen blistering
d) Uniform corrosion
Answer: c
Explanation: Hydrogen blistering is depicted in the given figure. It refers to the local deformation of metal with the entrapment of hydrogen molecules in the metal voids.
9. Which of the following type of corrosion is depicted in the given figure?
a) Hydrogen blistering
b) Hydrogen embrittlement
c) Filiform corrosion
d) Selective leaching
Answer: b
Explanation: Hydrogen embrittlement is depicted in the given figure. It refers to the loss of ductility and tensile strength of metal due to the formation of the respective metal hydride.
10. Which of the following metal is highly susceptible to hydrogen embrittlement?
a) Titanium
b) Nickel
c) Martensitic iron-base alloys
d) Titanium and martensitic iron-base alloys
Answer: d
Explanation: Hydrogen embrittlement refers to the brittle cracking failure of reactive metals due to the formation of metal hydrides. Titanium, ferritic, and martensitic iron-base alloys are susceptible to hydrogen embrittlement.
11. Which of the following type of corrosion in which corrosion occurs due to the presence of hydrogen sulfide?
a) Hydrogen embrittlement
b) Hydrogen blistering
c) Sulfide stress corrosion
d) Erosion corrosion
Answer: c
Explanation: Sulfide stress cracking occurs in the presence of water and hydrogen sulfide. It is highly concerned with petroleum industries and oil refining industries.
12. Which of the preventions is/are the preventions of hydrogen blistering?
a) Use of clean steel instead of rimmed steel
b) Applying metallic, inorganic and organic coatings
c) Use of substituting alloys such as nickel-based alloys
d) Use of clean steel instead of rimmed steel, applying metallic, inorganic and organic coatings and use of nickel-based alloys
Answer: d
Explanation: Preventions of hydrogen blistering are:
Use of clean steel instead of rimmed steel
Applying metallic, inorganic and organic coatings
Use of substituting alloys such as nickel-based alloys
Removing poisons such as sulfides, arsenic compounds, cyanides, and phosphorus ions.
13. Which of the following is/are the preventions of hydrogen embrittlement?
a) Baking of steels at low temperatures
b) Alloying with nickel or molybdenum reduces susceptibility
c) Practicing proper welding with low hydrogen welding rods
d) Baking of steels at low temperatures, alloying with nickel or molybdenum reduces susceptibility and practicing proper welding with low hydrogen welding rods.
Answer: d
Explanation: Preventions of hydrogen embrittlement are:
Baking of steels at low temperatures
Alloying with nickel and molybdenum reduces susceptibility
Practicing proper welding with low hydrogen welding rods.
This set of Corrosion Engineering Multiple Choice Questions & Answers focuses on “Exposure Techniques and its Factors – 1”.
1. Well-planned and executed tests usually result in reproducibility and reliability.
a) True
b) False
Answer: a
Explanation: Well-planned and executed corrosion tests result in reproducibility and reliability. The test needs to duplicate the actual plant service conditions as closely as possible.
2. Which of the following is/are the types of corrosion testing?
a) Laboratory testing
b) Pilot-plant testing
c) Field testing
d) Laboratory, pilot-plant and field testing
Answer: d
Explanation: Types of corrosion testings:
Laboratory testing
Pilot-plant testing
Actual plant service test
Field test.
3. Which of the following type of corrosion tests are usually best and more desirable?
a) Laboratory testing
b) Pilot-plant testing
c) Both laboratory and pilot-plant testing
d) Neither laboratory nor pilot-plant testing
Answer: b
Explanation: Pilot-plant tests are usually best and more desirable. It duplicates the intended large-scale operation environment by using the same raw materials, concentrations, temperature, and volume of corrosive solution to the area of metal exposed.
4. Which of the following is/are the purpose of corrosion testings?
a) Evaluation and selection of materials for a specific environment
b) To know the effect on the corrosion of metals by addition of inhibitors
c) To study the mechanism of corrosion
d) Evaluation and selection of materials for a specific environment, to know the effect on the corrosion of metals by addition of inhibitors and to study the mechanism of corrosion
Answer: d
Explanation: Purpose of corrosion testing are:
Evaluation and selection of materials for a specific environment
To know the effect of corrosion on metals by the addition of inhibitors
To study the mechanism of corrosion
To control the corrosion resistance of metal or corrosiveness of the environment.
5. What is the purpose of the salt-spray test?
a) To evaluate painted surfaces
b) To evaluate electroplated parts
c) To evaluate painted surfaces and electroplated parts
d) Neither to evaluate painted surfaces nor to evaluate electroplated parts
Answer: c
Explanation: Salt-spray test is a type of corrosion testing in which specimen is exposed to seawater or salt water in a box. It is usually used to evaluate painted surfaces and electroplated parts.
6. Which of the following statement is/are true regarding the Huey test?
a) Boiling 65% nitric acid is used as a corrosive solution
b) Used to evaluate the heat treatment of steels
c) Used to evaluate the heat treatment of stainless steels
d) Boiling 65% nitric acid is used as a corrosive solution and used to evaluate the heat treatment of stainless steels
Answer: d
Explanation: The Huey test is used to check the heat treatment of stainless steels. It uses boiling 65% nitric acid as a corrosive solution. Stainless steel is an alloy of iron, carbon, chromium, and nickel.
7. Which of the following specifications of the specimen is must increase the reliability of a corrosion test?
a) Chemical composition
b) Fabrication history
c) Metallurgical history
d) Chemical composition, fabrication history, and metallurgical history
Answer: d
Explanation: Exact chemical composition, fabrication history, and metallurgical history of a specimen are must increase the reliability of a corrosion test. Specimen with 1/16 to ¼ inch thick, 1 inch wide, and 2-inch-long are commonly employed for laboratory testing.
8. A standard surface condition is also desirable and necessary to facilitate comparison with other results.
a) True
b) False
Answer: a
Explanation: A surface finish of a specimen is one of the factors of corrosion. It is necessary to have a standard surface condition to facilitate comparison with another result. A common and widely used surface finish is produced by polishing with 120 numbered abrasive cloth.
9. Which of the following methods is/are used for the surface preparation of a specimen?
a) Polishing belts
b) Emery papers
c) Electrolytic polishing
d) Polishing belts, emery papers, and electrolytic polishing
Answer: d
Explanation: The surface finish of the specimen is one of the factors of corrosion. Surface preparation of a specimen can be done by using polishing belts, emery papers, and electrolytic polishing.
10. Which of the following type of corrosion testing is depicted in the given figure?
a) Field testing
b) Pilot-plant testing
c) Laboratory testing
d) Both field testing and pilot-plant testing
Answer: c
Explanation: Laboratory testing is one of the classifications of corrosion tastings. It serves as a most useful function as screening tests to determine which materials warrant further investigation.
11. Which of the following is the formula to calculate the minimum testing time for a corrosion test?
a) 2000/milli meters per year
b) 2000/mils per year
c) 1000/millimeters per year
d) 1000/mils per year
Answer: b
Explanation: A rough rule for checking results concerning minimum test time is 2000/mils per year. Here mils are also known as milli inches i.e. 1/1000th of an inch.
2000/mils per year = hours
12. Which of the following metals is/are subjected to increased attack in the presence of oxygen?
a) Aluminum and its alloys
b) Copper and its alloys
c) Cast iron and steel
d) Copper and its alloys, cast iron and steels
Answer: d
Explanation: Dissolved oxygen will be reduced cathodically into hydroxide ions in many of the corrosion systems and it increases the dissolution of metal anodically. Metals such as copper and its alloys, cast iron and steels are subjected to increase attack in the presence of oxygen.
13. Which of the following metals are resistant to dissolved oxygen?
a) Stainless steels
b) Aluminum and its alloys
c) Stainless steels, aluminum, and its alloys
d) Cooper and its alloys
Answer: c
Explanation: Metals such as aluminum and its alloys, stainless steel is highly resistant to oxygenated corrosive solutions. These metals result in the formation of respective stable oxides.
14. What is liquid-line corrosion?
a) Corrosion on the external surface of a fully-loaded water tank
b) Corrosion at the interface of liquid and gases in a pipeline or tank
c) Preferential corrosion of rivets over sheets in a storage container
d) Corrosion on the external surface of a half-loaded storage tank
Answer: b
Explanation: Liquid-line corrosion is a special type of corrosion that occurs at the interface of liquid and gas in a pipeline or tank. It occurs due to the availability of water vapor and oxygen at the interface along with impurities.
15. Which of the following is/are the cleaning methods after the exposure of specimen?
a) Sandblasting
b) Rubber-stopper
c) Use of chemical and solvents
d) Sandblasting, rubber-stopper and use of chemical and solvents
Answer: d
Explanation: Cleaning methods after the exposure of specimen:
Mechanical methods such as scraping, brushing, sandblasting and the rubber stopper
Chemical methods in which chemical solutions and solvents are used for removal
Electrolytic methods in which specimen is made cathode under an impressed current.
This set of Corrosion Engineering Multiple Choice Questions & Answers focuses on “Testing – Exposure Techniques and its Factors – 2”.
1. The Corrodibility of the metal in a corrosion test may decrease or increase as a function of time.
a) True
b) False
Answer: a
Explanation: Corrodibility of the metal is defined as the capability of being corroded. It may decrease or increase during the corrosion test as a function of time. It increases as it owing to the formation of a protective layer or it decreases as it owing removal of the more resistant surface layer.
2. Which of the following is/are the factors that affect corrosion testing?
a) Temperature
b) Dissolved oxygen
c) Nature of metal
d) Temperature, dissolved oxygen, and nature of metal
Answer: d
Explanation: The factors that affect corrosion testing are:
i. Temperature
ii. Dissolved oxygen
iii. Nature of metal
iv. The concentration of the corrosive solution
v. Specifications of the specimen .
3. Which of the following metals in which corrosion decreases with an increase in temperature in oxygenated corrosive solutions?
a) Copper and its alloys
b) Steels
c) Cast irons
d) Aluminum and its alloys
Answer: a
Explanation: Temperature is one of the important factors of corrosion. In many cases, an increase in temperature increases the corrosion rate of metals. Whereas it decreases in copper alloys due to the removal of dissolved oxygen.
4. Which of the following standard expression is used to measure the corrosion rate of a metal?
a) Mils per year = W/DAT
b) Mils per year = 534W/DAT
c) Milligrams decimeter per day = 534W/DAT
d) Milligrams decimeter per day = W/DAT
Answer: b
Explanation: Standard expression to measure the corrosion rate in mils per year = 534W/DAT.
Where D is the density of metal, W is weight loss in milligrams, A is the area of exposure in sq. inches, T is time in hours.
5. Which of the following units are used in terms of penetration of pits on a metal?
a) Milligram sq. decimeter per day
b) Mils per year
c) Both MDD and MPY
d) Neither MDD nor MPY
Answer: b
Explanation: Mils per year is commonly used corrosion rate expression as it measures corrosion rate in terms of depth of penetration of pit. Whereas milligram sq. decimeter per day measures the corrosion rate in terms of weight loss of metal.
6. Which of the following expression is used for electrochemical techniques to determine the corrosion penetration rate?
a) Corrosion penetration rate = K
b) Corrosion penetration rate = K
c) Corrosion penetration rate =
d) Corrosion penetration rate =
Answer: b
Explanation: The corrosion rate expression that is used for electrochemical techniques to determine corrosion penetration rate is K where a is the atomic weight of the metal, i is current density , n is the number of electrons lost, D is the density of metal, K is constant depends on the penetration rate desired.
7. Calculate the corrosion penetration rate of iron that corroding at an electrochemical corrosion rate of 1 microampere/sq. centimeters?
a) 0.212 mpy
b) 0.11 mpy
c) 0.46 mpy
d) 0.64 mpy
Answer: c
Explanation: Corrosion penetration rate = K
a = atomic weight of iron = 55.8 g
i = current density = 1 micrometer/sq. Centimeters
n = valency change = 2
D = density of iron = 7.86 g/cm 3
K = 0.129 for steel
Corrosion penetration rate = 0.129 * [ / ] = 0.46 mpy.
8. Which of the following is/are the corrosion testing’s for stainless steels?
a) Warren test
b) Streicher test
c) Huey test
d) Warren test, Streicher test and huey test
Answer: d
Explanation: Warren test, Streicher test and huey test are the corrosion testing’s for stainless steel. The primary function of these testing’s is to find out the sensitized stainless-steel metal specimens.
9. Which of the following method is the best approach to report the results of the pitting corrosion test?
a) Reporting the number of pits per unit area
b) Reporting maximum depth of a pit
c) Reporting average depth of pits
d) Reporting weight loss of a metal
Answer: b
Explanation: Pitting corrosion is one of the types of corrosion in which perforated metal is formed due to the formation of holes on the metal surface. The best way to report the corrosion testing of pitting is to report the maximum depth of a pit.
10. Which of the following factors are considered to evaluate the paint test?
a) Appearance of coating
b) Presence and extent of corrosion
c) Under film corrosion
d) The appearance of coating, presence, and extent of corrosion and under film corrosion
Answer: d
Explanation: The factors that are considered to evaluate the paint test are:
i. Appearance of coating
ii. Presence and extent of corrosion
iii. Under film corrosion.
This set of Corrosion Engineering Multiple Choice Questions & Answers focuses on “Corrosion of Plastics and Elastomers”.
1. The polymer is a large and heavy molecular chain formed from the interaction of many monomeric units.
a) True
b) False
Answer: a
Explanation: Polymers are the large and heavy molecular chains formed from the interaction of many monomeric units. It includes plastics, elastomers, and materials like polystyrene, etc.
2. Which of the following is/are characteristics of plastics?
a) High stiffness and strength
b) Less thermal and electrical conductivity
c) High corrosive resistance
d) High stiffness and strength, less thermal and electrical conductivity and high corrosive resistant
Answer: d
Explanation: Plastics are one of the classifications of polymers. It has high stiffness and strength, less thermal and electrical conductivity, and high corrosive resistance.
3. Which of the following statement is/are correct regarding elastomers?
a) It has high elastic properties
b) It has weak intermolecular forces of attraction between molecules
c) Rubber is a good example of an elastomer
d) Elastomers have high elastic properties, weak intermolecular forces of attraction and rubber is a good example of an elastomer
Answer: d
Explanation: Elastomers are the part of polymers which have high viscous and weak intermolecular forces of attraction between molecules. It has high elastic properties such as high resilience, elastic deformation. Rubber is a good example of an elastomer.
4. The corrosion mechanism of polymeric and metallic materials are the same in all corrosive environments.
a) True
b) False
Answer: b
Explanation: Polymeric materials corrode differently rather than processes associated with metallic corrosion. Metallic corrosion results in the electrochemical reactions with the dissolution of metal into metal ions. Whereas polymers result in physicochemical processes.
5. Which of the following is/are the physicochemical processes that occur in polymers?
a) Swelling
b) Dissolution
c) Bond rupture
d) Swelling, dissolution and bond rupture
Answer: d
Explanation: The physicochemical processes that occur in polymers due to the corrosive environment are:
Swelling
Dissolution
Bond rupture.
6. Which of the following is/are the causes for the bond rupturing in polymers?
a) Chemical reaction
b) Heat
c) Radiation
d) Chemical reaction, heat, and radiation
Answer: d
Explanation: Causes for the bond rupturing in polymers are:
Chemical reactions such as oxidation, reduction, and dehydrogenation, etc.
Heat
Radiation by sunlight.
7. Which of the following is/are the effects of polymeric corrosion?
a) Alteration of mechanical properties
b) Cracks formation due to internal stress
c) Loss of appearance
d) Alteration of mechanical properties cracks formation due to internal stress and loss of appearance
Answer: d
Explanation: Effects of polymeric corrosion:
Alteration in physical, chemical and mechanical properties
Cracks initiation and formation due to internal stress
Loss of appearance.
8. Which of the following is depicted in the given figure?
a) Metallic dissolution
b) Polymer-solvent interaction
c) Mechanism of polymeric degradation
d) Uniform corrosion of metals
Answer: b
Explanation: The given figure describes various layers formed by polymer-solvent interaction. These layers are solvent, liquid layer, Gel layer, Solid swollen layer, Infiltration layer, and polymer.
9. Which of the following corrosive environments that mostly results in polymeric dissolution?
a) Strongly oxidizing environments
b) Strong acids
c) Strong alkalis
d) Strong oxidizing environments, acids, and alkalis
Answer: d
Explanation: Corrosive environments that mostly results in polymeric dissolution are:
Strong oxidizing environments
Strong acids
Strong alkalis
Water-miscible solvents
Strong solvents.
10. What is Nelson’s method regarding the presentation of corrosion data?
a) A rapid and ready conversion table for various corrosion rate units
b) Schematic arrangement of corrosion data with the change in temperature and concentration
c) Formula oriented method to find corrosion rate
d) A specific corrosion test regarding galvanic corrosion of stainless steel
Answer: b
Explanation: Nelson’s method is a method of summarizing data of corrosion in which the corrosion rate of particular metal is reported with a change in temperature and concentration of the corrosive solution.
11. What is meant by nomography for corrosion rates?
a) Formula oriented method to find corrosion rate
b) A rapid and ready conversion table for various corrosion rate units
c) Schematic arrangement of corrosion data with the change in temperature and concentration
d) A specific corrosion rate measurement method
Answer: b
Explanation: Nomography for corrosion rate is a table in which it readily converts one corrosion rate unit into another corrosion another unit. Units of corrosion rate are namely mils per year , milligram sq. Decimeter per day .
This set of Corrosion Engineering Multiple Choice Questions & Answers focuses on “Materials – Metals and Alloys – 1”.
1. Which of the following properties of metal is often required to consider by corrosion engineer?
a) Physical properties
b) Mechanical properties
c) Chemical properties
d) Physical, mechanical and chemical properties
Answer: d
Explanation: Properties of a metal that is often required to consider by corrosion engineers are:
Physical properties such as density, modulus of elasticity
Mechanical properties such as strength, hardness
Chemical properties such as corrosion resistance, reactivity.
2. Which of the following is not a mechanical property of a metal?
a) Impact strength
b) Creep strength
c) Modulus of elasticity
d) Stress-rupture
Answer: c
Explanation: At a certain point, modulus of elasticity is considered as the physical property of a metal. Because it is an inherent property that cannot be changed by heat treatment or cold working.
3. Which of the following is/are the types of cast irons?
a) Gray cast iron
b) Malleable cast iron
c) Nodular cast iron
d) Gray cast iron, malleable cast iron, and nodular cast iron
Answer: d
Explanation: Cast iron is a generic term that applies to the high carbon-iron alloys containing silicon. Types of cast irons are gray cast iron, white cast iron, malleable cast iron, and nodular cast iron.
4. What is the composition of high-silicon cast iron named Durichlor that has the highest corrosion resistance among cast irons?
a) 14% silicon, 0.95% carbon and 3% molybdenum
b) 10% silicon, 1% carbon and 3% molybdenum
c) 14% silicon and 0.95% carbon
d) 10% silicon and 1% carbon
Answer: a
Explanation: The composition of Durichlor is 14% silicon, 0.95% carbon, and 3% molybdenum. It is a high-silicon cast iron that has the highest corrosion resistance among cast irons.
5. The excellent corrosion resistance of high-silicon irons is due to the formation of a passive SiO 2 surface layer.
a) True
b) False
Answer: a
Explanation: High-silicon cast iron is the type of alloy cast Irons that are formed with high silicon content . The excellent corrosion resistance of these alloys is due to the formation of a passive SiO 2 layer.
6. Which of the following metal is/are regarded as pure iron commercially?
a) Ingot iron
b) Armco iron
c) Wrought iron
d) Ingot and Armco iron
Answer: d
Explanation: Ingot and Armco iron are regarded as pure irons commercially. These are relatively weak and not used where strength is a major requirement. Whereas wrought iron is a mechanical mixture of slag and low-carbon steel.
7. Which of the following are the parameters of the iron-carbon diagram on the x and y-axis respectively?
a) Carbon percentage and Iron percentage
b) Carbon percentage and temperature
c) Temperature and carbon percentage
d) Iron percentage and temperature
Answer: b
Explanation: The iron-carbon phase diagram is an equilibrium phase diagram formed with carbon percentage and temperature parameters on the x and y-axis respectively. It consists of various phases such as alpha iron, austenite phase, delta iron, and its combinations.
8. Which of the following is/are the classification types of stainless steel?
a) Martensitic stainless steels
b) Ferritic stainless steels
c) Austenitic stainless steels
d) Martensitic, ferritic and austenitic stainless steels
Answer: d
Explanation: Stainless steel is a generic term that applies to iron-carbon-chromium and nickel alloy system. Types of stainless steels are Martensitic stainless steels, ferritic stainless steels, austenitic stainless steels, and precipitation-hardened steels.
9. Which of the following statements are correct regarding the austenite phase in an iron-carbon phase diagram?
a) It is non-magnetic in nature
b) The maximum percentage of carbon is 2.1%
c) It has a face-centered cubic structure
d) The austenitic phase has a face-centered cubic structure with a 2.1% maximum percent carbon and non-magnetic in nature.
Answer: d
Explanation: Austenite is one of the phases in the iron-carbon phase diagram. It has a face-centered cubic structure with 2.1% maximum percent carbon and it is non-magnetic in nature.
10. Which of the following properties of aluminum contributing to its widespread applications?
a) High corrosive resistance
b) Good strength-weight ratio
c) Nontoxic corrosion products
d) High corrosive resistance, good strength-weight ratio, and nontoxic corrosion products
Answer: d
Explanation: The properties of aluminum that contribute to its widespread applications are high corrosion resistance, good strength-weight ratio, nontoxic corrosion products, appearance, and electrical and thermal conductivity.
11. Which of the following metal is utilized in trucks, automobile engines, aircraft, and missiles?
a) Stainless steel
b) Carbon steels
c) Magnesium
d) Cast irons
Answer: c
Explanation: Magnesium is one of the lightest commercial metal with specific gravity 1.74. It is utilized in trucks, automobile engines, aircraft, and missiles. Whereas metals such as stainless steel, carbon steels, and cast irons are regarded as heavy metals.
12. Which of the following corrosion products of lead serve as protective films?
a) Lead sulfates
b) Lead oxides
c) Lead phosphates
d) Sulfates, oxides, and phosphates of lead
Answer: d
Explanation: Lead and its alloys are usually used piping, radiation shield, and storage batteries. It is resistant to corrosion in sulfuric acid, chromic acid, and phosphoric acid. Sulfates, oxides, and phosphates of lead are the corrosion products of lead that act as protective films.
13. Which of the following alloying element of stainless steel that attributes a large increase in stress-corrosion resistance?
a) Nickel
b) Chromium
c) Carbon
d) Nickel and chromium
Answer: a
Explanation: Stainless steel is a generic term that attributes to the alloy system of iron-carbon-chromium and nickel. Addition of nickel as alloying element up to 10% attributes in a rapid and large increase in stress-corrosion resistance of stainless steel.
14. Which of the following metal/alloy has the highest stress-corrosion resistance?
a) Aluminum
b) Inconel
c) Stainless steel
d) Titanium
Answer: b
Explanation: Typical composition of an Inconel is chromium 20-23%, iron 5%, molybdenum 8-10% and nickel around 60-65%. Inconel has the highest stress-corrosion resistance whereas aluminum, stainless steel, and titanium are prone to stress corrosion cracking.
15. Which of the following metals will have the same crystal structure as that of the given figure?
a) Zinc
b) Nickel
c) Titanium
d) Zinc and titanium
Answer: b
Explanation: The given figure depicts a face-centered crystal structure. Nickel is face-centered cubic structure material whereas zinc and titanium are hexagonal closed packed structures.
This set of Corrosion Engineering Question Bank focuses on “Materials – Metals and Alloys – 2”.
1. Which of the following metals will act as sacrificial metals in cathodic production?
a) Tin and zinc
b) Zinc only
c) Magnesium, zinc and magnesium
d) Magnesium and tin
Answer: c
Explanation: Sacrificial metals are the metals that corrode preferentially over the metallic structure that needs to be protected. This cathodic protection works on the principle of the galvanic effect. Tin, zinc, magnesium are the common sacrificial metals used.
2. Which of the following metal is/are corrosion resistant to hydrofluoric acid?
a) Hastelloy C
b) Monel
c) Hastelloy C and Monel
d) Titanium
Answer: c
Explanation: Hastelloy C and Monel are corrosion-resistant metals to hydrofluoric acid. Whereas titanium and most other metals usually corrode in hydrofluoric acid.
3. Which of the following metal plating is used for high-strength steels in aircraft to improve resistance to corrosion fatigue?
a) Cadmium
b) Magnesium
c) Zinc
d) Lead
Answer: a
Explanation: Corrosion fatigue is the simultaneous effect of fatigue and corrosion on a working metal. Cadmium plating is used for high-strength steels in aircraft to improve resistance to corrosion fatigue.
4. Which of the following metals will depend on the oxide layer for their corrosion resistance?
a) Titanium and stainless steels
b) Titanium, stainless steels, and aluminum and its alloys
c) Aluminum and its alloys
d) Aluminum and its alloy and titanium
Answer: b
Explanation: Corrosion resistance of the metal is the ability of a metal to withstand the effect of a corrosive environment. Titanium, stainless steel, and aluminum and its alloys will resist the corrosive environment with the formation of their oxide layer.
5. Which of the following metals has a Hexagonal closed packed structure?
a) Cadmium
b) Magnesium
c) Zirconium
d) Cadmium, magnesium, and zirconium
Answer: d
Explanation: Crystal structures are classified into 14 different types known as Bravais lattice based on the shape of the unit cell and position of atoms in it. Cadmium, magnesium, zirconium, titanium, zinc, and beryllium are examples of hexagonal closed packed structures.
6. Which of the following characteristics of titanium that account for much of its application in corrosive services?
a) Resistance to seawater and other chloride salt solutions
b) Resistance to hypochlorite’s and wet chlorine
c) Resistance to fuming nitric acid
d) Resistance to seawater, chloride salt solutions, hypochlorite’s, wet chlorine and fuming nitric acid
Answer: d
Explanation: Titanium is an excellent corrosion-resistant metal in many corrosive environments. The characteristics of titanium that account for much of its application in corrosion services are its resistance to seawater, chloride salt solutions, hypochlorite’s, wet chlorine, and fuming nitric acid.
7. Which of the following metals are regarded as refractory metals?
a) Niobium and tungsten
b) Molybdenum only
c) Niobium, molybdenum, and tungsten
d) Tungsten and molybdenum only
Answer: c
Explanation: Refractory metals are characterized by very high melting points with limited corrosion resistance. Tantalum, niobium, molybdenum, tungsten, and zirconium are regarded as refractory metals.
8. Which of the following metals that usually results in a porous and volatile oxide layer?
a) Magnesium
b) Molybdenum
c) Sodium
d) Magnesium, sodium, and molybdenum
Answer: d
Explanation: If the Pilling-bed worth ratio of a particular metal is less than 1 then it results in a porous, volatile, and thin oxide layer. Sodium, molybdenum, and magnesium are examples of this kind.
9. Which of the following metals are regarded as noble metals?
a) Iridium
b) Palladium
c) Ruthenium
d) Iridium, palladium, and ruthenium
Answer: d
Explanation: Noble metals are the metals that are characterized by highly positive potentials relative to the hydrogen electrode along with excellent corrosion resistance. This includes iridium, palladium, ruthenium, rhodium, osmium, gold, silver, and platinum.
10. What is the composition of aqua-regia that corrodes noble metals such as platinum, gold?
a) 3 parts of nitric acid and 1 part of hydrochloric acid
b) 3 parts of hydrochloric acid and 1 part of nitric acid
c) 1 part of hydrofluoric acid and 3 part of hydrochloric acid
d) 3 parts of hydrofluoric acid and 1 part of hydrochloric acid
Answer: b
Explanation: The composition of aqua regia is 3 parts of hydrochloric acid and 1 part of nitric acid. It corrodes/dissolves noble metals such as gold, platinum, and palladium.
11. What is the abbreviation of BMG regarding the type of materials?
a) Bulk metallic groups
b) Bulk metallic glasses
c) Body metallic glasses
d) Body metallic groups
Answer: b
Explanation: Bulk metallic glasses are the non-crystalline alloys that are formed with low critical cooling rates. These bulk metallic glasses exhibit useful engineering properties such as high mechanical strength and high corrosion resistance.
12. Metallic composites consist of a metallic matrix strengthened by metallic or nonmetallic fibers, filaments or whiskers.
a) True
b) False
Answer: a
Explanation: Composites are the type of materials that are formed by the combination of two or more materials. And metallic composites consist of a metallic matrix strengthened by metallic or nonmetallic fibers or whiskers. This includes boron, graphite, glass, and metal.
13. Which of the following factors that affect the corrosion of composites?
a) The corrosive specificity of an environment
b) Galvanic effect
c) Corrosive specificity of an environment and galvanic effect
d) Neither the corrosive specificity of an environment nor the galvanic effect
Answer: c
Explanation: The corrosion specificity of an environment and galvanic effect are the factors that affect the corrosion of composites. Thus, if the matrix and filament of a composite are close together in the galvanic series. galvanic effects are negligible.
14. Which of the following is the monomer of natural rubber?
a) Isoprene
b) Neoprene
c) Vinyl chloride
d) Styrene
Answer: a
Explanation: Natural rubber is a long-chain molecule of isoprene which is chemically known as polyisoprene. It is obtained from trees as liquid latex. The properties of natural rubber can be improved by the process known as vulcanization of rubber.
Answer: c
Explanation: The packing fraction of a given crystal structure is defined as the ratio of the volume of atoms in the unit cell to the volume of the unit cell. Given crystal structure is body-centered cubic and its packing fraction is 0.68.
This set of Corrosion Engineering Multiple Choice Questions & Answers focuses on “Materials – Thermoplastics”.
1. Which of the following is/are the classification of plastics based on the thermal behavior?
a) Thermoplastics
b) Thermosetting
c) Neither thermoplastics nor thermosetting
d) Thermoplastics and thermosetting
Answer: d
Explanation: Plastics can be categorized based on various parameters such as monomer units, temperature behavior, and structure. Thermoplastics and Thermosetters are the two types of plastics based on thermal behavior.
2. What is meant by thermoplastic?
a) It softens on heating and returns to original hardness on cooling
b) It hardens on heating and returns to original hardness on cooling
c) It hardens on heating and retains hardness on cooling
d) It softens on heating and retains hardness on cooling
Answer: a
Explanation: Thermoplastics is one of the type of plastics which softens on heating and returns to original hardness on cooling. Fluorocarbons, polyether, and nickel are examples of thermoplastics.
3. Which of the following thermoplastic is corrosion-resistant to all environments up to 550°F?
a) Polyvinyl chloride
b) Polystyrene
c) Teflon
d) Polyethylene
Answer: c
Explanation: Teflon is one of the fluorocarbons which is regarded as noble metals of plastics. It is corrosion-resistant to practically all environments up to 550°F. The monomer of Teflon is denoted as CF 2 =CF 2 .
4. Which of the following is the chemical name of nylon ?
a) Polyethylene terephthalate
b) Hexamethylene adipamide
c) Polytetrafluoroethylene
d) Polyvinyl fluoride
Answer: b
Explanation: The chemical name of nylon is hexamethylene adipamide. It is derived from the monomers of nylon that are hexamethylenediamine and adipic acid.
5. Which of the following thermoplastics is used for making eye lenses?
a) Polytetrafluoroethylene
b) Polyethylene terephthalate
c) Polymethyl methacrylate
d) Polyvinyl chloride
Answer: c
Explanation: Polymethyl methacrylate is the polymer of many methyl methacrylate monomeric units. It is used for making eye lenses as it is transparent to light. It is usually denoted as PMMA.
6. Which of the following is/are the monomers of nylon ?
a) Hexamethylenediamine
b) Adipic acid
c) Both Hexamethylenediamine and adipic acid
d) Neither Hexamethylenediamine nor adipic acid
Answer: c
Explanation: Hexamethylenediamine and adipic acid are the two monomers of nylon . The chemical formula of hexamethylenediamine and adipic acid is NH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -NH 2 and HOOC-CH 2 -CH 2 -CH 2 -COOH respectively.
7. Which of the following is/are the examples of thermoplastics?
a) Polypropylene
b) Polystyrene
c) Polyvinyl chloride
d) Polypropylene, polystyrene and polyvinyl chloride
Answer: d
Explanation: Thermoplastics are the type of plastics that soften on heating and return to their original hardness when cooled. Polypropylene, polystyrene, polyethylene, fluorocarbons, and polyvinyl chloride are examples of thermoplastics.
8. Which of the following thermoplastic monomer is depicted in the given figure?
a) Polystyrene
b) Teflon
c) Polyvinyl chloride
d) Polyurethane
Answer: a
Explanation: Styrene is depicted in the given figure and it is the monomer of polystyrene. It is an amorphous, colorless, rigid, and hard plastics. The monomer of polyvinyl chloride and Teflon is CH 2 =CH-Cl and CF 2 =CF 2 respectively.
9. Which of the following is the monomer of Polyvinyl chloride ?
a) CF 2 =CF 2
b) CH 2 =CH-Cl
c) COOH-CH 2 -CH 2 -CH 2 –CH 2 COOH
d) C 6 H 5 -CH=CH 2
Answer: b
Explanation: Vinyl chloride (CH 2 =CH-Cl) is the monomeric unit of polyvinyl chloride. It is used for piping and cable insulation extensively. CF 2 =CF 2 , COOH-CH 2 -CH 2 -CH 2 –CH 2 COOH and C 6 H 5 -CH=CH 2 are the monomers of Teflon, nylon, and polystyrene respectively.
10. Degradation of plastics is due to swelling, loss of mechanical properties, softening, hardening, and spalling.
a) True
b) False
Answer: a
Explanation: Corrosion of plastics is not the same as that of metals. Corrosion of metals results in the dissolution of metal ions whereas corrosion or degradation of plastics is due to swelling, loss of mechanical properties, softening, hardening, and spalling.
This set of Corrosion Engineering Multiple Choice Questions & Answers focuses on “Materials – Thermosetters”.
1. What is meant by thermosetting plastic?
a) It softens on heating and returns to original hardness on cooling
b) It hardens on heating and retains hardness on cooling
c) It hardens on heating and returns to original hardness on cooling
d) It softens on heating and retains hardness on cooling
Answer: b
Explanation: Plastics are readily divided into two types based on their thermal behavior. One is thermoplastic and another one is thermosetting. Thermosetting polymers are the polymers that harden on heating and retains hardness on cooling.
2. Which of the following is/are the example of thermosetting polymers?
a) Epoxies
b) Polyesters
c) Phenolics
d) Epoxies, polyesters, and phenolics
Answer: d
Explanation: Thermosetting polymers is one of the classifications of polymers based on the thermal behavior of polymers. Epoxies, polyesters, and phenolics are examples of thermosetting polymers.
3. Which of the following is/are the raw materials of Bakelite?
a) Phenol
b) Formaldehyde
c) Both phenol and formaldehyde
d) Neither phenol nor formaldehyde
Answer: c
Explanation: Bakelite is one of the most widely used thermosetting plastics for various domestic and industrial applications. Phenol or carbolic acid and formaldehyde are the raw materials of Bakelite.
4. Which of the following polyester is used in the space mirror satellite?
a) Mylar
b) Dacron
c) Vibrin
d) Dypol
Answer: a
Explanation: Thermosetting polymers such as Mylar, Dacron, Vibrin, and Dypol are categorize under polyester. The satellite was made of thin, reflective Mylar film.
5. Silicones are used for molding compounds, laminating resins, and insulation for electric motors and electronic equipment.
a) True
b) False
Answer: a
Explanation: Silicones are used for the molding compounds, laminating resins, and insulating for electric motors and electronic equipment because of its outstanding heat resistance. It can be demonstrated by Si–O–Si bond with alkyl groups on either side of the silicon atom.
6. What is the chemical name of the compound that is depicted in the given figure?
a) Formaldehyde
b) Bakelite
c) Urea
d) Vinyl chloride
Answer: c
Explanation: The compound that is depicted in the given figure is urea. It is one of the monomers of bauxite and beetle. It combines with formaldehyde to form plastics that used for the applications of kitchen dishware and utensils.
7. What is the abbreviation of FRP regarding reinforced plastics?
a) Filtrate-reinforced plastic
b) Fiber-reinforced plastic
c) Filter-reinforced plastic
d) Fume-reinforced polymer
Answer: b
Explanation: FRP can be abbreviated as Fiber-reinforced plastic regarding reinforced plastics. Carbon fibers, alumina fibers, an aramid fiber can be reinforced into plastics for better strength and corrosion resistance.
8. Which of the following thermosetting plastics that comes under phenolics?
a) Bakelite
b) Durez
c) Resinox
d) Bakelite, Durez, and Resinox
Answer: d
Explanation: Phenolics materials such as Bakelite, Durez, and Resinox are made up of phenol and formaldehyde. It uses for various applications such as electrical sockets, telephones, valves, and coatings.
9. Which of the following category that materials such as Epon, Durcon, and Araldite belong to?
a) Epoxies
b) Silicones
c) Phenolics
d) Polyesters
Answer: a
Explanation: Epon, Durcon, and Araldite belong to epoxies. These materials are the best combination of corrosion resistance and mechanical properties. It is mainly used as protective coatings, linings, and adhesives.
10. Which of the following is not a thermosetting plastic?
a) Dacron
b) Bakelite
c) Polystyrene
d) Polyester
Answer: c
Explanation: Thermosetting plastic is a plastic that hardens on heating and retains hardness on cooling. Dacron, Bakelite, and Polyester are examples of thermosetting plastics whereas Polystyrene is the example of thermoplastics.
This set of Corrosion Engineering Problems focuses on “Materials – Other Nonmetallics”.
1. Which of the following compounds that are present in ceramics?
a) Metallic elements
b) Non-metallic elements
c) Both metallic and non-metallic elements
d) Neither metallic nor non-metallic elements
Answer: c
Explanation: Ceramics are the other class of non-metallics. It usually consists of metallic and non-metallic elements. Magnesia, porcelain is the best examples of ceramics.
2. Which of the following is/are the examples of ceramics?
a) Brick
b) Stone
c) Fused silica
d) Brick, stone and fused silica
Answer: d
Explanation: Examples of ceramics are brick, stone, fused silica, stoneware, glass, clay, porcelain, concrete, abrasives, mortars, and high-temperature refractories.
3. Which of the following is/are the advantages of ceramics?
a) Resistance to higher temperatures only
b) Better corrosion resistance and resistance to higher temperatures
c) High abrasion resistance
d) Resistance to high temperatures, better corrosion resistance, and high abrasion resistance
Answer: d
Explanation: Advantages of ceramic materials are:
i. Resistance to higher temperatures
ii. Better corrosion resistance
iii. High abrasion resistance.
4. Which of the following is/are the disadvantages of ceramics?
a) Brittle in nature
b) Less tensile strength
c) Less resistance to thermal shocks
d) Brittle in nature, less tensile strength and less resistance to thermal shocks
Answer: d
Explanation: Disadvantages of ceramic materials are:
i. Brittle in nature
ii. Less tensile strength
iii. Less resistance to thermal shocks.
5. Which of the following is/are the ultra-tough ceramics that could be used in diesel engines?
a) Silicon carbide and zirconia
b) Silicon carbide, alumina, and zirconia
c) Zirconia only
d) Alumina and silicon carbide
Answer: b
Explanation: Much research is ongoing to produce ultra-tough ceramics such as silicon carbide, silicon nitride, alumina, and zirconia. This research aims to reduce the brittleness such that these materials could be used in diesel engines and gas turbines.
6. Acid brick is the material made from fireclay with a silica content about 10% greater than ordinary firebrick.
a) True
b) False
Answer: a
Explanation: Acid brick is the material made from fireclay with a silica content about 10% greater than ordinary firebrick. It is usually used for the construction of the floor of steel tanks that are subjected to acid spillage.
7. Which of the following statements regarding glass is/are correct?
a) It is an amorphous inorganic oxide
b) It composed of pure silica
c) It is mostly transparent in nature
d) It is an amorphous inorganic oxide, composed of pure silica and mostly transparent in nature
Answer: d
Explanation: Glass is an amorphous inorganic solid, mostly silica, cooled to a rigid condition without crystallization. Its transparency is used for equipment such as flowmeters and glass fibers.
8. What is the other name of fused quartz?
a) Vitreous silica
b) Amethyst
c) Citrine
d) Rutilated quartz
Answer: a
Explanation: Vitreous silica is also called fused silica. It has better thermal properties and corrosion resistance at high temperatures than most ceramics. Whereas amethyst, citrine, and rutilated quartz are the types of quartz.
9. Which of the following is/are the characteristics of carbon and graphite?
a) It has good thermal and electrical conductivity
b) Excellent thermal shock resistance
c) It has good thermal and electrical conductivity, excellent thermal shock resistance, weak and brittle as compared with metals
d) Weak and brittle as compared with metals and have excellent thermal shock resistance
Answer: c
Explanation: Carbon and graphite are the unique non-metallics that are good thermal and electrical conductors with excellent thermal shock resistance. They are weak and brittle as compared with metals.
10. Which of the following types of wood are used for corrosion applications?
a) Oak, redwood, and pine
b) Pine only
c) Redwood and oak
d) Redwood only
Answer: a
Explanation: Generally, wood is not a corrosion-resistant material but in particular circumstances, it can be used in the account of being economical. Cypress, pine, oak, and redwood are the types of woods used for corrosion applications.
This set of Corrosion Engineering Multiple Choice Questions & Answers focuses on “Prevention – Material Selection and Design – 1”.
1. The most common method of preventing corrosion is the selection of the proper metal or alloy for a particular corrosive service.
a) True
b) False
Answer: a
Explanation: There is no such single material that can be used in all environment conditions and all temperature ranges. So, it is important to select a proper metal or alloy for a particular corrosive service. It prevents or reduces the corrosion damage of the metallic structure.
2. Which of the following composition range is correct regarding stainless steel?
a) 11.5 to 30% chromium and 10 to 22% nickel
b) 11.5 to 30% chromium and 0 to 22% nickel
c) 0 to 30% chromium and 0 to 22% nickel
d) 0 to 30% chromium and 10 to 22% nickel
Answer: b
Explanation: Stainless steel is the generic name for a series of more than 30 different alloys with composition ranges from 11.5% to 30% chromium and 0 to 22% nickel and other alloying elements.
3. Which of the following types of corrosion in which stainless steels are more susceptible than ordinary steels?
a) Pitting corrosion
b) Stress-corrosion cracking
c) Intergranular corrosion
d) Stress-corrosion cracking, pitting and intergranular corrosion
Answer: d
Explanation: Stainless steels are more susceptible to localized corrosion such as intergranular corrosion, stress-cracking corrosion, and pitting corrosion than ordinary steels. Instability of oxide layer in severe corrosive conditions and sensitizing temperature are the reasons for the susceptibility of stainless steel.
4. Which of the following metal is the best material selection combination for the nitric acid environment?
a) Tin
b) Nickel and its alloys
c) Stainless steels
d) Steel
Answer: c
Explanation: Stainless steels are the best combination of metal for the nitric acid environment. Stainless steels readily form a passive oxide film in nitric acid. This minimizes or reduces the corrosion damage.
5. Which of the following metal is the best material selection combination for the caustic environment?
a) Titanium
b) Nickel and its alloys
c) Steels
d) Aluminum and its alloys
Answer: b
Explanation: Nickel and its alloys are the best combination of metal for the caustic environment. Metals such as titanium and high tensile strength steels are prone to caustic embrittlement.
6. Which of the following metal is the best material selection combination for distilled water?
a) Tin
b) Lead
c) Titanium
d) Nickel
Answer: a
Explanation: Tin is the best combination of metal for distilled water. Tin or tin coatings are almost always chosen as a container or piping material for very pure distilled water.
7. Which of the following metal is/are the correct combination for reducing or non-oxidizing environment?
a) Nickel and its alloys
b) Copper and its alloys
c) Stainless steels
d) Nickel, copper and its alloys
Answer: d
Explanation: Nickel, copper and its alloys are the correct combinations of metals for reducing or non-oxidizing environments. Whereas stainless steels and titanium alloys are stable in an oxidizing environment.
8. Which of the following material is used for handling hydrogen peroxide?
a) Commercially pure metals
b) Alloys
c) Both commercially pure metal and alloys
d) Neither commercially pure metals nor alloys
Answer: a
Explanation: Commercially pure metal such as aluminum is used for handling hydrogen peroxide. Alloys result in the decomposition of hydrogen peroxide due to the catalytic action of alloying elements.
9. Which of the following type of zirconium is used in an atomic-energy application?
a) Induction-melted zirconium
b) Arc-melted zirconium
c) Both arc-melted and induction-melted zirconium
d) Neither arc-melted nor induction melted zirconium
Answer: b
Explanation: Arc-melted zirconium is more corrosion resistant than induction-melted zirconium because of more impurities in the latter. Hence arc-melted zirconium is used in an atomic-energy application.
10. Which of the following is/are the different classes of non-metallics?
a) Ceramics and wood
b) Plastics and ceramics
c) Wood, ceramics, and plastic
d) Ceramics only
Answer: c
Explanation: The five general classes of non-metallics are:
Natural and synthetic rubber
Plastics
Ceramicsi
Carbon and graphite.
Wood.
11. Which of the following type of materials possess excellent corrosion and high-temperature resistance?
a) Metals
b) Plastics
c) Ceramics
d) Both ceramics and metals
Answer: c
Explanation: Ceramics are the class of materials that possess excellent corrosion and high-temperature resistance. But brittleness or less tensile strength is the primary limitation of ceramics.
12. Boiling seawater is less corrosive than that of hot seawater.
a) True
b) False
Answer: a
Explanation: Boiling seawater is less corrosive than that of hot seawater. Because the solubility of oxygen in seawater decreases with an increase in temperature. Reduction of oxygen results in severe metallic dissolution in many oxygenated corrosive solutions.
13. Which of the following belongs to the alteration of the environment to minimize corrosion?
a) Decreasing velocity
b) Removing oxygen and oxidizers
c) Changing concentration
d) Decreasing velocity, removing oxygen and oxidizers and changing the concentration
Answer: d
Explanation: Alteration of the environment is one of the measures to minimize corrosion. Alteration of the environment includes
Changing mediums
Lowering temperature
Decreasing velocity
Removing oxidizers
Changing concentrations.
14. Which of the following is/are the functions of magic devices or water-conditioning gadgets?
a) Prevent scaling
b) Destroy bacteria
c) Reduce water hardness
d) Prevent scaling, destroy bacteria and reduce water hardness
Answer: d
Explanation: Magic device or water-conditioning gadgets are the devices to control water corrosion. Purpose of these gadgets are
Prevent scaling
Destroy bacteria
Reduce water hardness
Reduces corrosion.
15. Which of the following metal combination is/are selected as per given requirement in the figure?
a) Gold – Iron
b) Steel – Stainless
c) Brass – Copper
d) Silver – Zinc
Answer: b
Explanation: The given figure indicates the galvanic metal combination. Hence metal combination should be as close as possible in the galvanic series to minimize the galvanic effect. Hence good metal combination is brass and copper.
This set of Corrosion Engineering Questions and Answers for Entrance exams focuses on “Prevention – Material Selection and Design – 2”.
1. Since corrosion is a penetrating action, it is necessary to make allowances for the reduction in thickness in designing pipes and tanks.
a) True
b) False
Answer: a
Explanation: Since corrosion is a penetrating action, it is necessary to make allowances for the reduction in thickness in designing pipes and tanks to meet the mechanical requirements of the service.
2. What should be the approximate thickness of a wall for better performance if the corrosion rate of that wall is estimated as 1/8 inches in 1 year?
a) 1/2 inches
b) 1/8 inches
c) 1/4 inches
d) 1/16 inches
Answer: c
Explanation: The approximate thickness of a wall should be twice that of the estimated corrosion rate to meet the mechanical requirements such as pressure, weight, and stress. Hence, the thickness of the given wall is 2* = ¼ inches.
3. Which of the following design of vessels is/are preferred regarding corrosion prevention?
a) Sharp-edged vessel only
b) Curve edged vessel only
c) Both sharp and curve edged vessel
d) Neither sharp nor curve edged vessel
Answer: b
Explanation: Sharp edges components result in the formation of crevices whereas has curve edged components result in proper circulation of solution throughout the component and eliminates crevice corrosion.
4. Which of the following is/are the design rules for corrosion prevention?
a) Weld rather than riveting containers
b) Design systems for easy replacement of components that fails rapidly
c) Avoid excessive mechanical stress and stress concentration
d) Weld rather than riveting containers, design systems for easy replacements of components that fail rapidly, and avoid excessive mechanical stress and stress concentration
Answer: d
Explanation: Design rules for corrosion preventions:
Weld rather than the riveting tank and other containers
Design systems for easy replacements of components that fails rapidly
Avoid excessive mechanical stress and stress concentration
Avoid electrical contact between two dissimilar metals.
5. Which of the following is the design rule to reduce erosion-corrosion?
a) Avoid excessive mechanical stress
b) Avoid sharp bend in piping systems
c) Avoid sharp bends in piping systems and provide thicker sections to reduce impingement effects
d) Avoid sharp bends in the piping system and excessive mechanical stress
Answer: c
Explanation: Erosion corrosion can be minimized by avoiding sharp bends in the piping system and provide a thicker section to reduce impingement effects. And the better material selection is also one of the factors to prevent erosion-corrosion.
6. Which of the following is not a design rule for corrosion prevention?
a) Riveting the tanks rather than welding
b) Specify operating and maintenance procedures
c) Tank bottoms should be sloped toward drain holes
d) Avoid electrical contact between dissimilar metals
Answer: a
Explanation: Certain design rules can reduce or minimize the effect of corrosion. That includes welding the tanks rather than riveting. This eliminates the formation of crevices at the riveting area and avoids crevice corrosion.
7. Uneven temperature distribution leads to higher corrosion rates and may result in stress-corrosion cracking failure.
a) True
b) False
Answer: a
Explanation: Stress-corrosion cracking is a combination of stress and a corrosive environment. Uneven temperature distribution leads to internal stress and results in stress-corrosion cracking failure.
8. Which of the following is/are included in the general term avoid heterogeneity?
a) Dissimilar metal contact
b) Different phases such as vapor spaces
c) Uneven heat and stress contribution
d) Dissimilar metal contact, different phases such as vapor spaces, and uneven heat and stress distribution.
Answer: d
Explanation: The design rule to avoid heterogeneity includes dissimilar metal contact, different phases such as vapor spaces, and uneven heat and stress distribution.
This set of Corrosion Engineering Multiple Choice Questions & Answers focuses on “ Corrosion Prevention – Inhibitors”.
1. An inhibitor is a chemical substance that added in small concentrations to an environment, to decrease the corrosion rate.
a) True
b) False
Answer: a
Explanation: An inhibitor is a chemical substance that added in small concentrations to an environment, to decrease the corrosion rate. It is also regarded as a retarding catalyst.
2. Which of the following is/are the types of inhibitors?
a) Adsorption inhibitors
b) Scavengers
c) Vapor-phase inhibitors
d) Adsorption inhibitors, scavengers, and vapor-phase inhibitors
Answer: d
Explanation: Following are the types of inhibitors:
i. Adsorption inhibitors
ii. Scavengers
iii. Vapor-phase inhibitors
iv. Hydrogen-evolution poisons
v. Oxidizers.
3. Which of the following is an example of adsorption-type inhibitors?
a) Arsenic
b) Sodium sulfite
c) Organic amines
d) Chromates
Answer: c
Explanation: Adsorption-type inhibitors are the type of inhibitors that adsorb on the surface of cathode or anode and alter its surface. Organic amines are examples of adsorption-type inhibitors.
4. Which of the following inhibitors are effective in acid solutions?
a) Oxidizers
b) Hydrogen-evolution poisons
c) Vapor-phase inhibitors
d) Oxidizers and hydrogen-evolution poisons
Answer: b
Explanation: Cathodic reduction of hydrogen ions to a hydrogen atom is the main driving force for the metallic dissolution in many acidic environments. It can be reduced or minimized with hydrogen-evolution poisons.
5. Which of the following is/are the examples of Hydrogen-evolution poisons?
a) Arsenic and Antimony
b) Sodium sulfite and hydrazine
c) Chromates and ferric salts
d) Organic amines
Answer: a
Explanation: Hydrogen-evolution poisons are the inhibitors that retard the rate of evolution of hydrogen gas in an acidic environment. Arsenic and Antimony are examples of hydrogen-evolution poisons.
6. Which of the following is/are the examples of scavengers?
a) Arsenic and Antimony
b) Chromates and ferric salts
c) Sodium sulfite and hydrazine
d) Organic amines
Answer: c
Explanation: Scavengers are the type of inhibitors that removes corrosive reagents from the solution. Sodium sulfite and hydrazine are examples of scavengers. 2Na 2 SO 3 +O 2 ==>2Na 2 SO 4 is the scavenging action of sodium sulfite.
7. Oxidizers such as chromates, nitrates, and ferric salts inhibit the corrosion of metal and alloys that demonstrate active-passive transition.
a) False
b) True
Answer: b
Explanation: Oxidizers such as chromates, nitrates, and ferric are one type of inhibitors that inhibit the corrosion of metal and alloys that demonstrate active-passive transition. Active-passive transition metals include iron and stainless steel.
8. Which of the following is/are the characteristics of the vapor phase inhibitor?
a) It has a very high vapor pressure
b) Inhibit the atmospheric corrosion without being contact with the metal surface
c) Effective in closed spaces
d) It has very high vapor pressure, inhibit atmosphere corrosion without being contact with the metal surface and very effective in closed spaces
Answer: d
Explanation: Vapor-phase inhibitors are very similar to organic adsorption-type inhibitors. Characteristics of vapor-phase inhibitors are:
i. It has a very high vapor pressure
ii. Inhibit the atmospheric corrosion without being contact with the metal surface
iii. Effective in closed spaces.
9. Which of the following phenomenon in which the inhibiting effect is sometimes greater than that would be achieved by either of the two or substances alone?
a) Galvanic effect
b) Cathodic protection
c) Synergistic effect
d) Inhibiting effect
Answer: c
Explanation: When two or more inhibiting substances are added to a corrosive system, the inhibiting effect is sometimes greater than that achieved by either of the two or more substances alone. This is called a synergistic effect.
10. Which of the following is/are the limitations of inhibitors?
a) It contaminates the environment
b) Inhibitors are toxic
c) Its efficiency decreases with time and temperature
d) It contaminates the environment, toxic in nature, and its efficiency decreases with time and temperature.
Answer: d
Explanation: Limitations of inhibitors:
i. It contaminates the environment
ii. Inhibitors are toxic in nature
iii. Its efficiency decreases with time and temperature
iv. It should not be used directly or indirectly in the preparation of food.
11. Which of the following inhibitor is used for aluminum in the hydrogen peroxide environment?
a) 2% boron trifluoride
b) Alkali metal nitrates
c) Sodium silicate
d) Benzoic acid
Answer: b
Explanation: Inhibitors are the chemical compounds that decrease the corrosion rate of metal in a specific environment. Alkali metal nitrates are used as inhibitors for the aluminum metal in the hydrogen peroxide environment.
12. Which of the following inhibitor is used for steel in 80% pure sulfuric acid?
a) 2% boron trifluoride
b) Sodium silicate
c) Alkali metal nitrates
d) Benzoic acid
Answer: a
Explanation: Inhibitors are very specific to a particular metal, environment, and the concentration of an environment. 2% boron trifluoride inhibitor is used for steel in 80% pure sulfuric acid.
13. Which of the following inhibitor is used for steel in the water?
a) Sodium silicate
b) Alkali metal nitrates
c) Benzoic acid
d) 2% boron trifluoride
Answer: c
Explanation: Inhibitors are the chemical compounds that decrease the corrosion rate of metal in a specific environment. Benzoic acid is used as an inhibitor for steel in water.
14. Which of the following phenomenon that occurs on metal surface during inhibition?
a) Adsorption only
b) Adsorption and phase layers
c) Phase layers only
d) Neither adsorption nor phase layers
Answer: b
Explanation: Inhibitors are the chemical compounds that decrease the corrosion rate of metal in a specific environment. Inhibition can be caused by both adsorption and phase layers on the metal surface.
This set of Corrosion Engineering Multiple Choice Questions & Answers focuses on “Cathodic and Anodic Protection – 1”.
1. Which of the following is/are the common electrochemical reactions that occur during corrosion?
a) M==>M + +ne
b) 2H + +2e=>H 2
c) O 2 +4H + +4e==>H 2 O
d) M==>M + +ne, 2H + +2e=>H 2 and O 2 +4H + +4e==>H 2 O
Answer: d
Explanation: The common electrochemical reactions that occur during corrosion are:
M==>M + +ne
2H + +2e=>H 2
O 2 +4H + +4e==>H 2 O
2. Cathodic protection is achieved by supplying electrons to the metal structure to be protected.
a) True
b) False
Answer: a
Explanation: Cathodic protection is achieved by supplying electrons to the metal structure to be protected. It can be done by using impressed current in the range of microamperes per unit area of the metallic structure.
3. Which of the following cases in which the metal structure is protected?
a) Current passes from metal to electrolyte
b) Current enters it from the electrolyte
c) Electrical contact with dissimilar metals
d) Connecting the positive terminal of the power supply
Answer: b
Explanation: Metallic structure can be protected when the impressed current is arranged to enter it from the electrolyte. Whereas current passes from metal to electrolyte, electrical contact with dissimilar metals, and connecting the positive terminal of the power supply results in accelerated corrosion.
4. Which of the following is/are the types of cathodic protection?
a) External impressed current supply
b) Sacrificial anode
c) External impressed current supply and sacrificial anode
d) Neither external impressed current supply nor sacrificial anode
Answer: c
Explanation: Cathodic protection is achieved by supplying electrons to the metal structure to be protected. Types of cathodic protection are i. External impressed current supply ii. Sacrificial anode.
5. Which of the following terminal of the power supply should be connected to the metal to be protected?
a) Negative terminal
b) Positive terminal
c) Both positive and negative terminals
d) Either positive or negative terminal
Answer: a
Explanation: As the conventional electrical theory states that current flows from to , the structure is protected if the negative terminal of the power supply is connected metallic structure.
6. Which of the following method is depicted in the given figure?
a) Anodic protection
b) Impressed current supply
c) Sacrificial anode
d) Anodic and cathodic protection
Answer: b
Explanation: Impressed current supply is a method of cathodic protection that is achieved by supplying electrons to the metal structure to be protected. The given figure depicted is impressed current supply method of an underground tank.
7. Which of the following material is/are used as an impressed-currents anode?
a) Graphite
b) Platinized titanium
c) Silicon-iron
d) Graphite, platinized titanium, and silicon-iron
Answer: d
Explanation: Materials that can be used as an impressed-currents anode are:
Graphite
Platinized titanium
Silicon-iron
Steel.
8. Which of the following materials is/are used as backfill around the anode in impressed currents?
a) Coke breeze
b) Gypsum
c) Bentonite
d) Coke breeze, gypsum, and bentonite
Answer: d
Explanation: Coke breeze, gypsum, and bentonite are the materials that are used as backfill material around the anode. These materials improve the electric contact between the anode and surrounding soil.
9. Which of the following protection method is depicted in the given figure?
a) Impressed-current supply method
b) Anodic protection
c) Sacrificial anode
d) Anodic protection and sacrificial anode
Answer: c
Explanation: Sacrificial anode method is one the type of cathodic protection in which a metal corrodes preferentially than the metallic structure. Sacrificial anodes are inexpensive and easily available in nature.
10. Which of the metallic structure will require more impressed current density for cathodic protection?
a) Water heaters in hot freshwater
b) Underground pipelines
c) The storage tank of H 2 SO 4
d) Reinforcement rods
Answer: c
Explanation: Impressed method current is an external supply of power to provide electrons to metallic structure that needs to be protected. The storage tank of H 2 SO 4 requires the highest current density per sq. feet due to the high corrosiveness of acid.
11. Which of the following reference electrode is used for cathodic-protection surveys?
a) Standard hydrogen electrode
b) Copper/copper sulfate reference electrode
c) Calomel electrode
d) Either calomel or standard hydrogen electrode
Answer: b
Explanation: Copper/copper sulfate reference electrode is used for cathodic protection surveys. The potential of a structure is determined with a high-resistance voltmeter. This electrode has the advantages of low cost, good accuracy, and ruggedness.
12. Which of the following is/are the typical sacrificial anodes?
a) Magnesium only
b) Zinc and magnesium
c) Aluminum-tin only
d) Magnesium, Zinc, and aluminum-tin
Answer: d
Explanation: Sacrificial anodes are metals that have a very high negative potential, which provides high current output. Magnesium, zinc, and aluminum-tin are typical examples of sacrificial anodes.
13. Which of the following is an impressed current anode that is efficient in a marine environment?
a) Platinized titanium
b) Silicon-iron
c) Scrap steel
d) Graphite
Answer: a
Explanation: Platinized titanium is an inert anode that is both efficient and expensive in nature. It is finding increased applications in marine environments.
14. Which of the following statements is/are correct about stray current?
a) It usually encountered in cathodic-protection systems
b) It refers to extraneous direct current in the earth
c) Acceleration corrosion will occur at the point where the current enters the soil
d) Stray current refers to extraneous direct current in the earth that usually encountered in cathodic protection systems and accelerated corrosion will occur at the point where current enters the soil
Answers: d
Explanation: Stray current refers to extraneous direct current in the earth that usually encountered in cathodic protection systems and accelerated corrosion will occur at the point where current enters the soil.
15. Which of the following is/are the preventions of stray current effect in an underground channel?
a) Use of bus conductor
b) Rearrangement of anodes
c) Use of bus conductor and rearrangement of anodes
d) Neither use of bus conductor nor rearrangements of anodes
Answer: c
Explanation: Stray current effect caused due to the densely buried underground pipelines in the vicinity of the cathodic protection system. It can be prevented by the use of bus conductors and rearrangements of anodes.
This set of Corrosion Engineering Questions and Answers for Campus interviews focuses on “Cathodic and Anodic Protection – 2”.
1. Which of the corrosion prevention method is used for reducing the maintenance cost of highway and bridges?
a) Sacrificial anode
b) Impressed current supply
c) Anodic protection
d) Use of inhibitors
Answer: b
Explanation: Impressed current supply is used as the corrosion prevention for reducing maintenance costs of big metallic structures such as highways and bridges. It also used to reduce the corrosion of reinforced steel.
2. Which of the following is depicted in the given figure?
a) Anodic protection
b) Impressed current supply
c) Stray current effect
d) Sacrificial anode
Answer: c
Explanation: The given figure depicts the stray current effect that usually caused to the dense pipelines in the vicinity of a tank or pipeline protected by the impressed current system.
3. Anodic protection is based on the formation of a protective film on metals by external applied anodic currents.
a) True
b) False
Answer: a
Explanation: Anodic protection is one of the corrosion prevention methods that is based on the formation of a protective film on metals by external applied anodic currents.
4. Which of the following metals can be protected using anodic protection?
a) Nickel and iron
b) Nickel, iron, and titanium
c) Titanium only
d) Nickel, iron, titanium, and magnesium
Answer: b
Explanation: Anodic protection can be used only for active-passive transition metals as it provides external current for the formation of a passive oxide layer. Active-passive transition metals include nickel, iron, aluminum, titanium, and its alloys.
5. A potentiostat is an electronic device that maintains a metal at a constant potential to a reference electrode.
a) True
b) False
Answer: a
Explanation: A potentiostat is an electronic device that maintains a metal at a constant potential to a reference electrode. It is required to protect a metal anodically by a passivating metal surface.
6. Which of the following corrosion prevention method is depicted in the given figure?
a) Sacrificial anode
b) Impressed current supply method
c) Use of inhibitors
d) Anodic protection
Answer: d
Explanation: Anodic protection of a storage tank is depicted in the given figure. A potentiostat is used to maintain the constant potential for a metallic structure against the reference electrode that results in passivity.
7. Which of the following auxiliary cathode is used for anodic protection?
a) Graphite
b) Platinized titanium
c) Platinum-clad electrode
d) Aluminum electrode
Answer: c
Explanation: It is necessary to have an inert auxiliary cathode such as a platinum-clad electrode as the anode provides external electric current to passivates the metallic structure.
8. Which of the following reference electrode is used in anodic protection?
a) Standard hydrogen electrode
b) Copper/copper sulfate reference electrode
c) Standard hydrogen electrode and calomel electrode
d) Calomel electrode
Answer: d
Explanation: The Calomel electrode is used to measure the potential maintained during the operation. It is connected to the third terminal of potentiostat whereas metal and auxiliary cathode are connected to first and second terminals respectively.
9. Which of the following is/are the advantages of anodic protection than cathodic protection?
a) Availability in extremely corrosive conditions
b) Low current requirement
c) Availability in extremely corrosive conditions and low current requirement
d) Very low installation cost
Answer: c
Explanation: Advantages of anodic protection than cathodic protection is:
i. Availability in extremely corrosive conditions
ii. Low current requirement.
10. Which of the following is/are the unique advantages of anodic protection?
a) To monitor instantaneous corrosion rate
b) Operating conditions can be established in the lab
c) It is applicable for all type of metals
d) To monitor instantaneous corrosion rate and operating conditions can be established in the lab
Answer: d
Explanation: Unique advantages of anodic protection are:
i. To monitor the instantaneous corrosion rate of a metal
ii. Operating condition of anodic protection can be precisely established in the lab.
This set of Corrosion Engineering Multiple Choice Questions & Answers focuses on “Corrosion Prevention – Coatings – 1”.
1. A thin coating of metallic and inorganic materials can provide a satisfactory barrier between the metal and its environment.
a) True
b) False
Answer: a
Explanation: A thin coating of metallic, inorganic, and organic material can provide a satisfactory barrier between the metal and its environment. Because it minimizes the exposure of native metal to the corrosive environment.
2. Which of the following is/are the purposes of coatings?
a) To acts as a sacrificial metal
b) To act as an effective barrier
c) Either to act as sacrificial metal or to act as an effective barrier
d) Neither to act as sacrificial metal nor to act as an effective barrier
Answer: c
Explanation: Coatings are the relatively thin material portion on the surfaces of native metal to avoid direct exposure to the corrosive environment. The purpose of coatings is either to act as sacrificial metal or to act as an effective barrier.
3. Which of the following is/are the methods to apply metallic coatings?
a) Electrode position
b) Flame spraying
c) Cladding
d) Electrode position, flame spraying, and cladding
Answer: d
Explanation: Methods to apply metallic coatings are:
i. Electrode position
ii. Flame spraying
iii. Cladding
iv. Hot dipping
v. Vapor deposition.
4. What is the reason for the localized attack on the base metal due to the porosity of coatings?
a) Crevice formation
b) Galvanic effect
c) Initiation of pits
d) Crevice formation and galvanic effect
Answer: b
Explanation: The localized attack on the base metal due to the porosity of coatings is dueto two-metal corrosion or galvanic effect. Because metal coating and base metal are electrically connected in a corrosive environment.
5. Which of the following is/are the examples for metal-coated articles?
a) Silverware
b) Galvanized steel
c) Tin cans
d) Silverware, galvanized steel, and tin cans
Answer: d
Explanation: Sacrificial metals such as zinc, tin, and precious metals such as silver, gold, platinum is used as metallic coatings for various applications. Silverware, galvanized steel, and tin cans are examples of metallic coatings.
6. What is meant by electrodeposition?
a) Immersing native metal in a solution of the metal to be plated
b) Hot rolling of two metals together to get a composite sheet
c) A wire or powder through melting flame is blown onto the surface to be protected
d) Coating metal is vaporized electrically to deposit on the metals to be coated
Answer: a
Explanation: Electrode position is an immersion of native metal in a solution of the metal to be plated with direct current passing through them. It is also called electroplating.
7. Which of the following is/are the factors of electroplating that effects efficiency?
a) Temperature and composition of the bath
b) Composition of bath and time
c) Temperature, the composition of the bath, time and current density
d) Current density and composition of the bath
Answer: c
Explanation: Factors that affect the efficiency of electroplating are:
i. Temperature
ii. Current density
iii. Time
iv. Composition of bath.
8. What is the general purpose of each coating in a three-layered coating of an automobile bumper?
a) Inner coating – adhesion, intermediate coating – corrosion protection and top layer – appearance
b) Inner coating – corrosion protection, intermediate coating – adhesion and top layer – appearance
c) All layers for corrosion resistance
d) All layers for appearance
Answer: a
Explanation: In general, multiple layered metallic structures consist of inner coating for adhesion such as copper, intermediate coating for corrosion resistance such as nickel and top coatings for appearance such as chromium.
9. What is meant flame spraying metallic coating?
a) Hot rolling of two metals together to get a composite sheet
b) A wire or powder through melting flame is blown onto the surface to be protected
c) Coating metal is vaporized electrically to deposit on the metals to be coated
d) Immersing native metal in a solution of the metal to be plated
Answer: b
Explanation: Flame spraying metallic coating is a method of metal coating in which a wire or powder through the melting flame is blown onto the surface to be protected. Oxygen, acetylene, and propane are used for melting flame.
10. Which of the following is/are the application of flame spraying?
a) Bridges
b) Refrigeration equipment
c) Ship hulls
d) Bridges, refrigeration equipment and ship hulls
Answer: d
Explanation: Application of flame spraying include vessels of all kinds, bridges, ship hulls, refrigeration equipment, and many fabricated steel products. Low melting point metals such as zinc, tin, and lead are used.
11. What is meant by metal cladding?
a) Immersing native metal in a solution of the metal to be plated
b) Coating metal is vaporized electrically to deposit on the metals to be coated
c) Hot rolling of two metals together to get a composite sheet
d) A wire or powder through melting flame is blown onto the surface to be protected
Answer: c
Explanation: Metal cladding is a method of hot rolling two metals together to get a composite sheet. High-strength aluminum alloys and commercial pure aluminum are rolled together to provide the corrosion barrier.
12. Cladding is a great economical advantage in that the corrosion barrier as the expensive material is backed up by inexpensive material by minimizing corrosion.
a) True
b) False
Answer: a
Explanation: Cladding is a great economical advantage in that the corrosion barrier as the expensive material is backed up by inexpensive material by minimizing corrosion.
13. What is meant by vapor deposition?
a) A wire or powder through melting flame is blown onto the surface to be protected
b) Coating metal is vaporized electrically to deposit on the metals to be coated
c) Hot rolling of two metals together to get a composite sheet
d) Immersing native metal in a solution of the metal to be plated
Answer: b
Explanation: Vapor deposition is a method of metal coating in that coating metal is vaporized electrically to deposit on the metals to be coated. It is usually used for high strength parts for missiles and rockets.
14. What is meant by diffusion coatings?
a) Immersing native metal in a solution of the metal to be plated
b) Coating metal is vaporized electrically to deposit on the metals to be coated
c) Heat treatment to cause alloy formation by diffusion of one metal into the other
d) Hot rolling of two metals together to get a composite sheet
Answer: c
Explanation: Diffusion coatings involve heat treatment to cause alloy formation by diffusion of one metal into the other. It is also called as surface alloying. It improves various properties such as wear-resistance and corrosion resistance at the surface.
15. Which of the following is/are the types of diffusion coatings?
a) Sherardizing – zinc
b) Chromizing – chromium
c) Alonizing – aluminum
d) Sherardizing – zinc, chromizing – chromium and alonizing – aluminum
Answer: d
Explanation: Types of diffusion coatings:
i. Sherardizing – zinc
ii. Chromizing – chromium
iii. Alonizing – aluminum
iv. Carburizing – carbon
v. Nitriding – nitrogen.
This set of Corrosion Engineering Assessment Questions and Answers focuses on “Corrosion Prevention – Coatings – 2”.
1. What is meant by chemical conversion regarding coatings of a metal?
a) Coating metal is vaporized electrically to deposit on the parts to be coated
b) Coatings produced by corroding the metal surface to form an adherent protective layer
c) Hot rolling of two metals together to produce composite sheet
d) A metal wire or powder through the melting flame is blown onto the surface to be protected
Answer: b
Explanation: Chemical conversion is one of the surface coating methods in that coatings are produced by corroding the metal surface to form an adherent protective layer.
2. Which of the following is/are the examples of chemical conversion?
a) Bonderizing
b) Parkerizing
c) Chromatizing
d) Bonderizing, parkerizing, and chromatizing
Answer: d
Explanation: Bonderizing, parkerizing, and chromatizing are examples of chemical conversion. Automobile bodies are best known for phosphatizing treatment. Anodized aluminum with a protective film Al 2 O 3 is another example.
3. In general, coatings should not be used where the environment would rapidly attack the substrate material.
a) True
b) False
Answer: a
Explanation: In general, coatings should not be used where the environments would rapidly attack the substrate material because one defect or small area of exposed metal would result in rapid degradation.
4. Which of the following is/are the examples of organic coatings?
a) Paints
b) Varnishes
c) Lacquers
d) Paints, varnishes and lacquers
Answer: d
Explanation: Organic coatings are widely used to protect more metals on a tonnage basis than other corrosion combating processes. Organic coatings include paints, varnishes, and lacquers.
5. Which of the following is/are factors to consider for organic coatings?
a) Surface preparation only
b) Surface preparation and selection of primary coating
c) Surface preparation and selection of primary and top coatings
d) Selection of primary and top coatings
Answer: c
Explanation: Factors to consider for organic coatings are:
i. Surface preparation usually is done by sandblasting
ii. Selection of primary coatings for strong adhesive bonding
iii. Selection of top coating for appearance and corrosion resistance.
6. What is the purpose of surface preparation?
a) Surface roughening for mechanical bonding
b) Removal of dirt, rust and mill scale
c) Removal of welding flux and other impurities
d) Surface roughening for mechanical bonding, removal of dirt, rust, mill scale, welding flux, and other impurities
Answer: d
Explanation: Surface preparation is a crucial part of the stability of coatings. It roughens the surface to obtain mechanical bonding, removal of dirt, rust, mill scale, welding flux, and other impurities.
7. Which of the following is/are the methods for surface preparation for coating application?
a) Sandblasting and chipping
b) Wire brushing and flame cleaning
c) Sandblasting, chipping, wire brushing and flame cleaning
d) Sandblasting, chipping and flame cleaning
Answer: c
Explanation: Methods for surface preparation for coating application are:
i. Sandblasting
ii. Wire brushing
iii. Flame cleaning
iv. Chipping
v. Scarping.
8. Which of the following paints are widely used for corrosion applications?
a) Vinyl and epoxy paints
b) Asphalts and bituminous paints
c) Iron oxide and titanium oxide paints
d) Alkyds and red lead
Answer: a
Explanation: A variety of paints are available in the market for various corrosion applications. It includes asphalts, bituminous paints, red lead, iron oxide, titanium oxide, alkyds, vinyl, and epoxies. Among them, vinyl and epoxies are the class of paints that are widely used for corrosion applications.
9. Which of the following is/are the characteristics of primers or primary coatings?
a) It contains rust-inhibitive pigments only
b) Adequate wettability and short drying time
c) Short drying time, adequate wettability and it contains rust-inhibitive pigments
d) It contains rust-inhibitive pigments and short drying time
Answer: c
Explanation: Characteristics of primary coatings are:
i. It contains rust-inhibitive pigments
ii. Adequate wettability
iii. Short drying time.
10. Which of the following is/are the advantages of coal-tar coatings?
a) Excellent corrosion resistance to fresh and seawater
b) Excellent corrosion resistant to fresh, seawater and soil immersion
c) High abrasive resistance
d) Stable coating
Answer: b
Explanation: Coal-tar coatings are excellent corrosion resistant to fresh, seawater, and soil immersion. Whereas its abrasive resistance and stability of coating are its limitations.
This set of Corrosion Engineering Multiple Choice Questions & Answers focuses on “Mineral Acids – Sulfuric Acid”.
1. Which of the following is/are the examples of mineral acids?
a) Sulfuric acid and nitric acid
b) Hydrochloric acid and hydrofluoric acid
c) Sulfuric, nitric, hydrochloric, hydrofluoric and phosphoric acid
d) Sulfuric, nitric, hydrochloric and hydrofluoric acid
Answer: c
Explanation: Mineral acid or inorganic acid is the acid derives from one or more inorganic compounds on dissolution with water. This includes sulfuric acid, nitric acid, hydrochloric acid, hydrofluoric acid, and phosphoric acid.
2. Which of the following acid is produced relatively higher than other acids?
a) Nitric acid
b) Sulfuric acid
c) Phosphoric acid
d) Hydrofluoric acid
Answer: b
Explanation: Sulfuric acid is produced relatively higher than other acids. The chemical formula for sulfuric acid is H 2 SO 4 . It is produced by absorbing water into oleum.
3. What are the principal uses of sulfuric acid?
a) Production of hydrochloric acid
b) Manufacturing of dyes, fertilizers, and drugs
c) Pickling of steels and other metals
d) Production of hydrochloric acid, manufacturing of dyes, fertilizers and drugs and pickling of steels
Answer: d
Explanation: Principle uses of sulfuric acid are:
Production of hydrochloric acid and other chemicals
Manufacturing of dyes, fertilizers, drugs, explosives, and rayon
Pickling of steels and other metals
Laboratory usage.
4. Which of the following method is used to produce sulfuric acid?
a) Contact process
b) Ostwald process
c) Solvay process
d) Haber process
Answer: a
Explanation: Sulfuric acid is produced by the contact process or leads chamber process. It is produced by absorbing SO 3 with water. This process accounts for 70% of world production.
5. Which of the following statements is/are true regarding the contact process?
a) Conversion of sulfur dioxide to sulfur trioxide takes place
b) Vanadium oxide is used as a catalyst
c) It accounts for 70% of the world’s production
d) Conversion of sulfur dioxide to sulfur trioxide takes place in the presence of vanadium catalyst and it accounts for 70% world’s production
Answer: d
Explanation: Contact process:
Sulfur compounds such as copper sulfide are burned to get SO 2
Catalytic conversion of sulfur dioxide to sulfur trioxide takes place
Absorption of SO 3 into water produces sulfuric acid.
6. Which of the following concentration of sulfuric acid in which the corrosion rate of steel is minimum?
a) Less than 30%
b) Greater than 70%
c) 30% – 70%
d) above 110%
Answer: b
Explanation: Ordinary steels are widely used for various concentrations of sulfuric acid greater than 70% purity. Dilute acids attack steel very rapidly and result in faster degradation.
7. Which of the following are the functions of the given graph on the x and y-axis respectively?
a) Temperature and concentration of acid
b) Corrosion rate and temperature
c) The concentration of acid and temperature
d) The concentration of acid and corrosion rate
Answer: c
Explanation: The given graph is an isocorrosion chart. It is a streamlined method devised to present the corrosion data. The concentration of acid and temperature are the functions of the isocorrosion chart on the x and y-axis respectively.
8. Which of the following is/are the factors that affect the corrosion resistance of steel in concentrated sulfuric acid?
a) High velocity
b) Temperature of acid
c) Aeration
d) High velocity, temperature, and aeration
Answer: d
Explanation: High velocity, the temperature of acid and aeration are the factors that affect the corrosion resistance of steel in concentrated sulfuric acid .
9. Which of the following metal is not corrosion resistant to sulfuric acid?
a) Grey cast iron
b) Duriron
c) Durimet 20
d) Lead
Answer: a
Explanation: Grey cast iron is not corrosion resistant to sulfuric acid as it penetrates the metal along with the graphite flakes. Though the corrosion rates are small but the metal may split open in service.
10. Lead is used extensively for sulfuric acid in the lower concentration ranges .
a) False
b) True
Answer: b
Explanation: Lead is used extensively for sulfuric acid in the lower concentration ranges . It is not recommended above 70% purity is due to the solubility of lead sulfate surface film in the acid.
11. Which of the following is/are the applications of Duriron because of its corrosion resistance and inherent hardness?
a) To manufacture pumps, valves, and fans
b) To make heat exchangers
c) Impressed–current anodes
d) To manufacture pumps, valves, fans, heat exchangers and impressed-current anodes
Answer: d
Explanation: Duriron is high-silicon cast iron with high corrosion resistance and inherent hardness. It is used to manufacture pumps, valves, fans, heat exchangers, and impressed-current anodes.
12. Which of the following alloying elements are not recommended in the sulfuric acid environment?
a) Chromium
b) Nickel
c) Molybdenum
d) Nickel and molybdenum
Answer: c
Explanation: Alloying elements are added in base metal to exhibit certain specific properties such as corrosion resistance, thermal properties, or mechanical properties. Here molybdenum is not recommended as an alloying element in high-silicon cast iron for sulfuric acid application.
This set of Corrosion Engineering Question Paper focuses on “Mineral Acids – Nitric Acid and Hydrochloric Acid”.
1. Which of the following is/are the class1 corrosion resistance materials in nitric acid?
a) High-silicon cast irons
b) Stainless steels
c) Titanium
d) High-silicon cast iron, stainless steels, and titanium
Answer: d
Explanation: Class1 materials are the materials that are used for a particular environment and it is generally recommended for a variety of conditions of temperature and concentration. Class1 materials for nitric acid includes high-silicon cast irons, stainless steels, and titanium.
2. Which of the following steels will have less corrosion rate in boiling 65% nitric acid?
a) 4.5% chromium steel
b) 8% chromium and 8% nickel steel
c) 18% chromium and 8% nickel stainless steel
d) 18% chromium stainless steel
Answer: c
Explanation: The corrosion resistance of steel in nitric acid increases as the alloying elements such as chromium and nickel increases. The minimum percentage of chromium required for adequate corrosion resistance is 15%.
3. Duriron exhibits excellent corrosion resistance in concentrations over 45% at temperatures including boiling.
a) True
b) False
Answer: a
Explanation: Duriron is high-silicon cast iron with 14.5% silicon exhibits excellent corrosion resistance in concentrations over 45% at temperatures including boiling. It is a class1 material in the usage of nitric acid.
4. The corrosion resistance of Durichlor to nitric acid is better than that of Duriron.
a) True
b) False
Answer: b
Explanation: Durichlor is high-silicon cast iron with 14.5% silicon and 3% molybdenum. It is not better corrosion resistant to nitric acid than that of Duriron. Because molybdenum doesn’t increase the corrosion resistance to nitric acid.
5. What are the principal applications of Duriron?
a) Cast forms of pumps, valves, heat exchangers for chemical plant
b) In manufacturing and handling of nitric acid
c) In the ammonia oxidation process
d) Cast forms of pumps, valves, heat exchangers for chemical plant, in manufacturing and handling of nitric acid and ammonia oxidation process
Answer: d
Explanation: Principal applications of Duriron are:
i. Cast forms of pumps, valves, heat exchangers for chemical plants
ii. In manufacturing and handling of nitric acid
iii. In the ammonia oxidation process.
6. Which of the following statements is/are true about titanium?
a) It has excellent corrosion resistance to fuming nitric acid
b) It is used as an oxidizer in fuel systems for rockets
c) It has excellent corrosion resistance to fuming nitric acid and it is used as an oxidizer in fuel systems for rockets
d) It doesn’t exhibit pyrophoric tendencies in red fuming nitric acid
Answer: c
Explanation: Titanium has excellent corrosion resistance to fuming nitric acid and it is used as an oxidizer in fuel systems for rockets. Whereas it exhibits pyrophoric tendencies in red fuming nitric acid if the water content of the acid is below 1.5% and the nitrogen dioxide content is above 2.5%.
7. Which of the following is/are the class2 corrosion-resistant materials in nitric acid?
a) Aluminum and Stainless steels
b) Aluminum, Hastelloy, and Inconel
c) Hastelloy and Inconel
d) Hastelloy and Titanium
Answer: b
Explanation: Class2 corrosive resistance materials of nitric acid are the materials that are used in only certain specific conditions of temperature and concentration because of limited corrosion resistance and cost. This includes Aluminum, Hastelloy, and Inconel.
8. Which of the following polymer has excellent corrosion resistance to nitric acid?
a) Teflon
b) Polyvinyl chloride
c) Polystyrene
d) Polyethylene
Answer: a
Explanation: Teflon shows excellent corrosion resistance to nitric acid. Glass filled Teflon is widely used for rotating rings in mechanical seals for nitric acid pumps.
9. Which of the following is/are the class3 corrosion-resistant materials in nitric acid?
a) Copper and its alloys
b) Nickel and its alloys
c) Low-alloy steels
d) Low-alloy steels, copper, nickels and their alloys
Answer: d
Explanation: Class3 materials are recommended for use in a particular environment because of its less corrosion resistance. This includes copper and its alloys, nickel and its alloys and low-alloy steels.
10. Which of the following metal is used for hydrochloric acid to avoid contamination?
a) Titanium
b) Tantalum
c) Molybdenum
d) Cupronickels
Answer: b
Explanation: Hydrochloric acid is the most difficult of the common acids to handle regarding corrosion. Tantalum is an expensive metal but it is often used to avoid contamination.
11. Which of the following is/are the class1 corrosion resistance materials in hydrochloric acid?
a) Chlorimet 2 and Chlorimet 3
b) Hastelloy B and C
c) Zirconium and molybdenum
d) Chlorimet 2 and 3, Hastelloy B and C, Zirconium, Molybdenum and Tantalum
Answer: d
Explanation: Class1 materials are the materials that are used for a particular environment and it is generally recommended for a variety of conditions of temperature and concentration. Class1 materials for hydrochloric acid include Chlorimet 2 and 3, Hastelloy B and C, Zirconium, Molybdenum, and Tantalum.
12. Duriron has better corrosion resistance than Durichlor in hydrochloric acid.
a) False
b) True
Answer: a
Explanation: Durichlor is high-silicon cast iron with 14.5% silicon and 3% molybdenum is more corrosion resistant than Duriron in hydrochloric acid.
13. Which of the following is/are the class2 corrosion resistance materials in hydrochloric acid?
a) Bronzes and Cupronickels
b) Hastelloy D and Duriron
c) Bronzes, Stainless steels, Bronzes, Cupronickels, Hastelloy D and Duriron
d) Stainless steels and Duriron
Answer: c
Explanation: Class2 corrosive resistance materials of nitric acid are the materials that are used in only certain specific conditions of temperature and concentration because of limited corrosion resistance and cost. This includes bronzes, stainless steels, bronzes, cupronickels, Hastelloy D, and Duriron.
14. Which of the following metals will have a high influence on aeration and oxidizing agents in hydrochloric acid?
a) Copper and its alloys
b) Nickel and its alloys
c) Nickel-molybdenum alloys, copper, nickel and their alloys
d) Nickel-molybdenum alloys
Answer: c
Explanation: Nickel-molybdenum alloys, copper, nickel, and their alloys will have a high influence on aeration and oxidizing agents in hydrochloric acid. These materials show excellent corrosion resistance in reducing conditions but are rapidly attacked in oxidizing conditions.
15. Which of the following impurity in hydrochloric acid results in pitting corrosion?
a) Ferrous chloride
b) Ferric chloride
c) Potassium chloride
d) Sodium chloride
Answer: b
Explanation: Ferric chloride in small amounts is more destructive than oxygen in hydrochloric acid. It initiates pits and results in pitting corrosion on various metals in the hydrochloric environment.
This set of Corrosion Engineering Multiple Choice Questions & Answers focuses on “Mineral Acids – Hydrofluoric Acid and Phosphoric Acid”.
1. Which of the following material is/are primarily used for hydrofluoric acid?
a) High-silicon cast iron
b) Magnesium
c) Aluminum
d) Glass and stoneware
Answer: b
Explanation: Materials such as high-silicon cast iron, aluminum, glass, and stoneware are generally resistant to many acids but these are readily attacked in hydrofluoric acid. Whereas magnesium is practically immune to corrosion because of the formation of a surface fluoride film.
2. Hydrofluoric acid and fluorine are toxic and extreme care are mandatory in the handling of these materials.
a) True
b) False
Answer: a
Explanation: Hydrofluoric acid and fluorine are toxic and extreme care are mandatory in the handling of these materials. Metals such as magnesium are used for some shipping containers because of the formation of a surface fluoride film.
3. Which of the following metal is suitable in handling high concentrations of hydrofluoric acid?
a) Stainless steel
b) Brass
c) Steel
d) Titanium
Answer: c
Explanation: Steel is suitable for handling hydrofluoric acid ranging concentration from 60% to 100%. The corrosion of steel rapidly increases as the concentration decreases below 60%.
4. Which of the following is/are the impurities in commercial hydrofluoric acid that decreases corrosion of steel?
a) Sulfuric acid
b) Fluosilicic acid
c) Neither sulfuric acid nor fluosilicic acid
d) Both sulfuric acid and fluosilicic acid
Answer: d
Explanation: Usually impurities such as sulphuric acid and fluosilicic acid are present in commercial hydrofluoric acid that reduces the corrosion of steel.
5. Which of the following metal is an outstanding material that resists all concentrations of hydrofluoric acid at all temperatures?
a) Wrought Monel
b) Steel
c) Stainless steel
d) Hastelloy C
Answer: a
Explanation: Wrought Monel is an outstanding metal in that it resists all concentrations of hydrofluoric acid at all temperatures including boiling. Monel is the best selection of material for hydrofluoric environment applications.
6. Why straight chromium stainless steels and austenitic stainless steels are not recommended for hydrofluoric acid applications?
a) Due to susceptibility to crevice
b) Due to limited corrosion resistance
c) Due to susceptibility to pitting
d) Sensitive to erosion-corrosion
Answer: c
Explanation: Straight chromium stainless steels and austenitic stainless steels are not recommended for hydrofluoric acid applications due to their susceptibility to pitting corrosion. Whereas of stainless steel is sensitive to erosion-corrosion.
7. Which of the following materials is/are widely used for phosphoric acid?
a) 316 stainless steel
b) Durimet 20
c) Neither 316 stainless steel nor Durimet 20
d) Both 316 stainless steel and Durimet 20
Answer: d
Explanation: 316 stainless steel and Durimet 20 are the two alloys that are widely used for phosphoric acid. These alloys show the very little attack in concentrations up to 85% and temperatures including boiling.
8. Which of the following materials exhibits poor corrosion resistance to phosphoric acid?
a) Aluminum and brass
b) Aluminum, brass, steel, cast iron, ferritic and martensitic stainless steels
c) Steel and cast iron
d) Ferritic and martensitic stainless steels
Answer: b
Explanation: Metals such as aluminum, brass, steel, cast iron, ferritic, and martensitic stainless steels exhibit poor corrosion resistance to phosphoric acid. Whereas 316 stainless steel and Durimet 20 are widely used for phosphoric acid.
9. Which of the following is/are the impurities that cause corrosion in commercial phosphoric acid?
a) Fluorides
b) Chlorides
c) Sulfuric acids
d) Fluorides, chlorides and sulfuric acid
Answer: d
Explanation: Corrosion by phosphoric acid depends on the methods of manufacturing and impurities present in that commercial acid. Impurities that are usually present in commercial phosphoric acid are fluorides, chlorides, and sulfuric acid.
10. Which of the following non-metallic has the highest corrosive resistance to the phosphoric acid with temperature?
a) Teflon
b) Graphite
c) Polyvinyl chloride
d) Polyethylene
Answer: a
Explanation: Teflon is a non-metallic material that has the highest corrosion resistance to phosphoric acid up to 550°C. Teflon is also known as polytetrafluoroethylene (CF 2 =CF 2 ).
This set of Corrosion Engineering Multiple Choice Questions & Answers focuses on “Environments – Organic Acids”.
1. Which of the following materials is/are used for handling acetic acid?
a) Type 316 and 304 Stainless steels
b) Copper and Bronzes
c) Duriron and Hastelloy C
d) Hastelloy C, Durimet 20, Duriron, Copper, Bronzes and 316 and 304 stainless steels
Answer: d
Explanation: Acetic acid is the most important organic acid from the standpoint of quantity produced. Hastelloy C, Durimet 20, Duriron, Copper, Bronzes, and 316 and 304 stainless steels are widely used for handling acetic acid.
2. Which of the following metals will switch positions in acetic acid as the temperature gets increased?
a) Copper and stainless steel
b) Stainless steel and nickel
c) Steel and copper
d) Aluminum and nickel
Answer: a
Explanation: Acetic acid exhibits unusual corrosion behavior with an increase in temperature. Copper and stainless-steel switch positions as the temperature are increased. Copper shows little corrosion at high temperatures whereas stainless steels corrode rapidly and vice versa.
3. Organic acids are relatively weaker than the inorganic acids because they are slightly ionized.
a) True
b) False
Answer: a
Explanation: Organic acids are relatively weaker than the inorganic acids because they are slightly ionized. The relatively high degree of ionization of inorganic acid results in greater electrochemical corrosion of metal.
4. Which of the following is the most corrosive organic acid?
a) Acetic acid
b) Formic acid
c) Ethanol
d) Acetone
Answer: b
Explanation: Formic acid is one of the strongest and most corrosive organic acids. It mainly results in stress-corrosion cracking of various metals at various conditions. The chemical formula of formic acid is HCOOH.
5. Which of the following metal is prone to stress corrosion cracking in methanol?
a) Nickel
b) Copper
c) Titanium
d) Stainless steel
Answer: c
Explanation: Methanol is the derivate of methane and it is also called methyl alcohol. The chemical of methanol is CH 3 OH. Titanium is prone to stress corrosion cracking in methanol with the presence of chloride impurities.
6. Which of the following metals will have high corrosion rates in aerated acetic acid?
a) Aluminum and its alloys
b) Copper and its alloys
c) Titanium and its alloys
d) Nickel and its alloys
Answer: b
Explanation: Copper and its alloys will be highly affected by aeration in acetic acid and it increases with an increase in temperature. It can be prevented by deaeration and decrease in temperature.
7. Which of the following impurities that affect the corrosion rate of carbon steel in benzene solvent?
a) Oxygen
b) Butyric acid
c) Oxygen and butyric acid
d) Zinc dust
Answer: c
Explanation: Oxygen and butyric acid are the impurities that affect the corrosion rate of carbon steel in benzene solvent. It can be prevented by eliminating oxygen.
8. What are the parameters that affect the corrosion rate of metal in organic acids?
a) Solvent composition
b) The solubility of corrosion products
c) Oxygen solubility
d) Solvent composition, the solubility of corrosion products and oxygen solubility
Answer: d
Explanation: Parameters that affect the corrosion rate of metals in organic acids are:
i. Solvent composition and structure
ii. The solubility of corrosion products
iii. Oxygen solubility.
9. Which of the following is/are the corrosion prevention methods in organic acids?
a) Selection of materials and drying
b) Selection of materials, drying, deaeration, and neutralization of the solvent
c) Deaeration and neutralization of the solvent
d) Drying and deaeration
Answer: b
Explanation: Corrosion prevention methods in organic acids:
i. Selection of materials
ii. Drying
iii. Deaeration
iv. Neutralization of the solvent.
10. The application of electrochemical protection methods in organic acids is restricted due to low electrical conductivity.
a) True
b) False
Answer: a
Explanation: Application of electrochemical protection methods in organic acids is restricted due to low electrical conductivity. As we know cathodic and anodic protection is based on electrical conductivities of metallic structure and medium.
This set of Corrosion Engineering Multiple Choice Questions & Answers focuses on “Environments – Alkalies”.
1. What is meant by caustic embrittlement?
a) Decrease in compressive strength due to caustic accumulation
b) The phenomenon of metal to become brittle due to caustic accumulation at the rivets
c) Entrapment of caustic content between atoms to cause brittleness
d) The phenomenon of metal to become more tensile due to caustic accumulation
Answer: b
Explanation: Caustic embrittlement is the phenomenon of metal to become brittle due to caustic accumulation at the rivets. The cold working of rivets is the main reason for caustic embrittlement.
2. Which of the following statements is/are correct regarding caustic embrittlement?
a) Mild carbon steels are susceptible to caustic embrittlement
b) It occurs in concentrated hydroxide environment
c) It occurs around the rivets
d) Mild carbon steels are susceptible to caustic embrittlement in concentrated hydroxide environment around the rivets
Answer: d
Explanation:
i. Mild carbon steels are susceptible to caustic embrittlement
ii. It occurs in concentrated hydroxide environment
iii. It occurs around the rivets due to cold working.
3. Which of the following is/are the preventions of caustic embrittlement?
a) Optimize stress concentration
b) Avoid caustic environment
c) Use of nickel-based alloys, avoid caustic environment and optimize stress concentration
d) Use mild carbon steels
Answer: c
Explanation: Preventions of caustic embrittlement are:
i. Optimize stress concentration
ii. Avoid caustic environment
iii. Use of nickel-based alloys.
4. Which of the following common alkalies that results in stress-corrosion cracking of steel?
a) Caustic soda
b) Caustic soda and caustic potash
c) Caustic potash
d) Sodium carbonate
Answer: b
Explanation: Caustic soda and caustic potash are the common alkalies that result in stress-corrosion cracking of steel. It usually occurs in high concentrations only.
5. Which of the following metal is suitable under all conditions of concentration and temperature in caustic soda?
a) Nickel
b) Aluminum
c) Titanium
d) Carbon steel
Answer: a
Explanation: Nickel is suitable under all conditions of concentrations and temperatures in the caustic environment. The corrosion resistance of material directly proportional to the nickel content of an alloy.
6. Aluminum is a very poor resistant material for handling caustic environments and rapidly attacked even by dilute solutions.
a) False
b) True
Answer: b
Explanation: Aluminum is a very poor resistant material for handling caustic environments and rapidly attacked even by dilute solutions. But it is adopted in an ammoniacal environment such as refrigeration systems and storage tanks.
7. Which of the following metal results in stress corrosion cracking in an ammoniacal solution?
a) Aluminum and its alloys
b) Nickel and its alloys
c) Copper and its alloys
d) Stainless steels
Answer: c
Explanation: Copper and its alloys result in stress corrosion cracking in ammoniacal solutions. The decomposition of organic materials containing nitrogen has caused stress corrosion cracking.
8. Oxygen is the primary cause of cracking in ammoniacal solution rather than nitrogen.
a) True
b) False
Answer: a
Explanation: Oxygen is the primary cause of cracking, with as little as 0.01 ppm required in the ammoniacal solution. A slip step or film rupture is a mechanical method of this cracking.
9. Which of the following can be used to inhibit stress corrosion cracking in ammoniacal solutions?
a) Addition of 0.2% water
b) Addition of 0.025% hydrazine in refrigeration
c) Addition of oxidizing agents
d) Either addition of 0.2% water or addition of 0.025% hydrazine in refrigeration
Answer: d
Explanation: Oxygen and oxidizing agents are the primary cause of stress corrosion cracking in ammoniacal solutions. It can be inhibited by the addition of 0.25% of water or the addition of 0.025% hydrazine in refrigeration.
10. Which of the following is/are used for ammoniacal solution applications?
a) Cast iron and steel
b) 430 and 304 type stainless steels
c) Cast iron, steel, 430 and 304 type stainless steels
d) Copper and cast irons
Answer: c
Explanation: Ammonia and ammoniacal solutions generally do not present a difficult corrosion problem. We usually use cast iron, steel, and 430, 304 type stainless steels for low and high temperatures respectively.
This set of Corrosion Engineering Multiple Choice Questions & Answers focuses on “ Environments – Atmospheric Corrosion”.
1. Which of the following is/are the classifications of atmospheres regarding atmospheric corrosion?
a) Industrial
b) Marine
c) Rural
d) Industrial, marine and rural
Answer: d
Explanation: Atmospheric corrosion can be defined as the corrosion of metals in surrounding corrosive environment. It can be classified into three types namely industrial, marine and rural atmospheres.
2. Which of the following is/are the primary causes of atmospheric corrosion?
a) Moisture
b) Oxygen
c) Moisture, oxygen and sulfur contaminants
d) Sulfur contaminants only
Answer: c
Explanation: The primary causes of atmospheric corrosion is moisture, oxygen and sulfur contaminants. Absence of either moisture or oxygen in at least form will result in no corrosion.
3. Corrosion of steel on the seacoast is 400 to 500 times is more corrosive than in a desert area.
a) True
b) False
Answer: a
Explanation: Corrosion of steel on the seacoast is 400 to 500 times is more corrosive than in a desert area. This due to the contamination of atmosphere with sodium chloride and other impurities at the seacoast.
4. How many times that industrial corrosion is more corrosive than rural atmospheres?
a) 10 to 20
b) 50 to 100
c) 30 to 50
d) 100 to 150
Answer: b
Explanation: Industrial corrosion is 50 to 100 times more corrosive than desert areas. It is due to the presence of Sulphur burned gases such as SO 2 , SO 3 and these results in the formation of sulfurous and sulfuric acids in the presence of moisture.
5. Which of the following is/are the reasons for more corrosiveness of industrial atmosphere than rural atmosphere?
a) Formation of sulfurous and sulfuric acid
b) Ejection of corrosive ammoniacal solutions
c) Formation of sulfurous and sulfuric acid and ejection of corrosive ammoniacal solutions
d) High levels of carbon dioxide
Answer: c
Explanation: Formation of sulfurous and sulfuric acid from sulfur burning gases and ejection of corrosive ammoniacal solutions are the reasons of industrial corrosion. Whereas carbon dioxide is not corrosive in nature.
6. Which of the following alloying elements increase resistance of steel to atmospheric corrosion?
a) Copper
b) Nickel
c) Chromium
d) Copper, nickel and chromium
Answer: d
Explanation: Steel is the most widely used metal for various metallic structures in all atmospheres. The resistance of steel can be improved by alloying elements such as copper, nickel and chromium. This is due to formation of stable, thick and adherent protective film.
7. Which of the following metals are widely used for atmospheric applications?
a) Copper and lead
b) Copper, lead, aluminum and galvanized steel
c) Galvanized steel only
d) Galvanized steel and copper
Answer: b
Explanation: Copper, lead, aluminum and galvanized steel are widely used for atmospheric corrosion applications. Improving the corrosion resistance of steel with small alloy additions is now commonly used along with weight-saving applications.
8. Which of the following alloys is also called as weathering steels?
a) Low-alloy steels used for atmospheric applications
b) High-alloy steels used for atmospheric applications
c) Low-alloy copper alloys
d) Low-alloy aluminum alloys
Answer: a
Explanation: Low-alloy steels used for atmospheric applications is also known as weathering steels. It is also used in weight-saving applications and to increase durability of paint coatings.
9. Sheltered corrosion is the type of corrosion where moisture condenses or accumulates and does not dry out for long periods of time.
a) False
b) True
Answer: a
Explanation: Sheltered corrosion is the type of corrosion where moisture condenses or accumulates and does not dry out for long periods of time. Corrosion on inside of an automobile door and inside of a partially filled automobile gasoline tank are the examples of sheltered corrosion.
10. Which of the following phenomenon that results in rapid corrosion on the inside of large storage tanks occurs when moisture-laden salt air is drawn in?
a) Sheltering
b) Breathing
c) Exhalation
d) Crevice
Answer: b
Explanation: Breathing results in rapid corrosion on the inside of large storage tanks occurs when moisture-laden salt air is drawn in. This can be prevented by protective coatings for steels and blanketing with nitrogen or dry air inside the tank.
This set of Basic Corrosion Engineering Questions and Answers focuses on “Environments – Sea Water and Fresh Water”.
1. Which of the following is/are true regarding seawater?
a) It contains 3.4% salt
b) It has a pH around 8
c) It is a good electrolyte with high electrical conductivity
d) Seawater is a good electrolyte with high electrical conductivity with 3.4% salt and pH around 8
Answer: d
Explanation: Seawater is a good electrolyte with high electrical conductivity with 3.4% salt and pH around 8. It can cause galvanic and crevice corrosion to various metals.
2. Which of the following is/are the factors that affect corrosion in seawater?
a) Temperature and velocity
b) Oxygen content and biological organisms
c) Temperature, velocity, oxygen content and biological organisms
d) Temperature, velocity and oxygen content
Answer: c
Explanation: The factors that affect the corrosion of materials in seawater are:
i. Temperature
ii. Velocity
iii. Oxygen content
iv. Biological organisms.
3. Which of the following region of the seacoast environment have high corrosion based on the given figure?
a) Quiet seawater
b) Splash region
c) High tide area
d) Mud line
Answer: b
Explanation: Greatest corrosion occurs in the splash region due to alternate wetting and drying and also aeration. We know oxygen and moisture are the primary requirements for corrosion of metals.
4. Which of the following regions of the seacoast environment shows the effect of the pitting of metals and alloys?
a) Quiet seawater
b) High tide region
c) Low tide region
d) Splash region
Answer: a
Explanation: Pitting is extremely localized corrosion which results in holes or cavities. Quiet seawater in the region of the seacoast environment that shows the effect of the pitting of metals and alloys. An increase in the velocity of a corrosive solution decreases the pitting tendency of a metal.
5. Corrosion by seawater at greater depth is usually decreased because of the lower temperature.
a) False
b) True
Answer: b
Explanation: Corrosion by seawater at greater depth is usually decreased because of the lower temperature. It decreases by 40°F for one-mile depth.
6. Which of the following impurities contaminates the brackish water due to tidal action in rivers and bays near the ocean?
a) Chlorides
b) Bromides
c) Hydrides
d) Metal oxides
Answer: a
Explanation: Chloride ions are the impurities that contaminate the brackish water due to the tidal action in rivers and bays near the ocean. The source of these chloride ions is sodium chloride in seawater.
7. Which of the following metals have high resistance to crevices in quiet seawater?
a) Hastelloy C
b) Titanium
c) Hastelloy C and Titanium
d) Nickel-copper alloy
Answer: c
Explanation: Hastelloy C and titanium have high resistance to crevices in quiet seawater. Due to this, these metals are used for various corrosive seawater applications. Whereas nickel-copper alloy shows less resistance.
8. Which of the following alloy has high cavitation resistance that usually used for ship propellers and pumps impellers in seawater?
a) Titanium
b) Stellite
c) 17-7 Stainless steel
d) Nickel aluminum bronze
Answer: b
Explanation: Stellite is a cobalt-chromium alloy with high cavitation resistance that usually used for ship propellers and pump impellers in seawater. Composition of Stellite is 27–32% chromium, 4–6% tungsten, 0.9–1.4% carbon, with additions of nickel, iron, silicon, manganese, and molybdenum and cobalt as balance.
9. Which of the following factors that affect the corrosivity in freshwater?
a) Oxygen content
b) Hardness
c) Chloride content
d) Oxygen content, hardness and chloride content
Answer: d
Explanation: Factors that affect the corrosivity in freshwater are:
i. Oxygen content
ii. Hardness
iii. Chloride and sulfur content.
10. Which of the following type of water is more corrosive?
a) Hard water
b) Hard and soft water
c) Soft water
d) High-purity water
Answer: c
Explanation: In hard water, carbonates often deposit on the metal surface and protect it from corrosion. Whereas in soft water protective deposits do not form. Hence, soft water is more corrosive than hard water and high-purity water.
11. Which of the following metals are widely used for handing freshwater?
a) Cast iron
b) Stainless steel
c) Galvanized steel
d) Cast iron, stainless steel, and galvanized steel
Answer: d
Explanation: Cast iron, stainless steel, steel, and galvanized steel are widely used for handling freshwater. Metals such as copper, brass, aluminum, monel, and cupronickels are also used with the factors of temperature, contamination, and longer life.
12. Which of the following corrosion defects that affect the reliability of tubing?
a) Selective weld metal attack
b) Improper pickling and heat treatment
c) Residual stresses, selective weld metal attack, improper pickling, and heat treatment
d) Selective weld metal attack and residual stresses
Answer: c
Explanation: Corrosion defects that affect the reliability of tubing are:
i. Inadequate alloying
ii. Selective weld metal attack
iii. Improper pickling
iv. Residual stresses
v. Improper heat treatment.
13. Corrosion decreases with an increase in the purity of water.
a) True
b) False
Answer: a
Explanation: Corrosion decreases with increasing purity of the water because of less solid and gases and increasing electrical resistance. Resistance is a measure of water purity.
14. Which of the following types of corrosion has been seen in stainless steels in high purity water containing oxygen?
a) Cracking of solution-quenched stainless steel only
b) Intergranular attack and cracking of solution-quenched steel
c) Intergranular attack only
d) Neither intergranular corrosion nor cracking of solution-quenched steel
Answer: b
Explanation: Intergranular corrosion and cracking of solution-quenched stainless steel and alloys have been observed in high-purity water containing oxygen.
15. Which of the following metals/alloys are used for handling high-purity water in nuclear applications?
a) Zirconium and its alloys
b) Stainless steels
c) Inconel and Incoloy
d) Zirconium and its alloys, stainless steels, Inconel and Incoloy
Answer: d
Explanation: Zirconium and its alloys, stainless steels, Inconel and Incoloy are the metals/alloys that are used for handling high-purity water in nuclear applications.
This set of Corrosion Engineering Multiple Choice Questions & Answers focuses on “Environments – Soil and Aerospace”.
1. The corrosivity of soils varies over a wide range because of the variety of composition.
a) True
b) False
Answer: a
Explanation: The corrosivity of a particular solution depends on its composition. So, the corrosivity of soils varies over a wide range because of the variety of composition.
2. Which of the factors that affect the corrosiveness of soils?
a) Moisture
b) Acidity
c) Oxygen
d) Moisture, oxygen, acidity and stray currents
Answer: d
Explanation: The factors that affect the corrosiveness of soils are moisture, oxygen, acidity, alkalinity, the permeability of air and water, stray currents, and biological organisms.
3. Which of the following is a good measure of corrosivity?
a) Thermal conduction
b) Electrical resistance
c) Thermal resistance
d) Mechanical properties
Answer: b
Explanation: Electrical resistance is a good measure of corrosivity of a corrosive solution. Higher electrical resistance lowers the corrosivity of a solution. Dry soils are generally not very corrosive due to high electrical resistance.
4. Which of the following type of corrosion is/are dominant due to backfills such as stones, cinders, wood, and metal?
a) Crevice corrosion
b) Pitting corrosion
c) Crevice and pitting corrosion
d) Neither crevice nor pitting corrosion
Answer: c
Explanation: Crevice and pitting corrosion are the types of corrosion that dominate due to backfill such as stones, cinders, wood, and metal. Because these foreign particles result in the formation of crevices.
5. Which of the following is/are true regarding underground structures?
a) Ordinary carbon steels and cast irons are commonly used
b) Organic coatings can be used
c) Cathodic protection is applied to protect it from corrosion
d) Usually made of carbon steel and cast irons with or without organic coatings and supported by a cathodic protection system
Answer: d
Explanation: Underground structures are usually made up of ordinary carbon steels and cast irons with or without organic coatings. These structures are also supported by a cathodic protection system to minimize corrosion.
6. Which of the following type of corrosion is pre-dominate in underground corrosion?
a) Aerobic corrosion
b) Anaerobic corrosion
c) Aerobic and anaerobic corrosion
d) Neither aerobic nor anaerobic corrosion
Answer: c
Explanation: The anaerobic type of attack is pre-dominate in underground corrosion. It is due to the non-availability of oxygen as it decreases with an increase in depth.
7. Which of the following areas of aircrafts face severe corrosion problems?
a) Fuel tank due to oxidizers and fuel
b) High-temperature corrosion in blast nozzles
c) The outer structure of the plane due to vacuum
d) Fuel tank due to oxidizers and fuel, high-temperature corrosion in blast nozzles
Answer: d
Explanation: Fuel tank due to oxidizers and fuel and high-temperature corrosion in blast nozzles are the two areas that aerospace face severe corrosion problems. Whereas the hard vacuum of space does not cause corrosion.
8. Which of the following materials is/are used for blast nozzles in aerospace?
a) Aluminum oxide and cemented tungsten carbide
b) Aluminum oxide cemented tungsten carbide and boron carbide
c) Cemented tungsten carbide only
d) Aluminum oxide and boron carbide
Answer: b
Explanation: Aluminum oxide, cemented tungsten carbide, and boron carbide is the materials that are used for blast nozzles in aerospace. These materials are also known as refractory materials.
9. Which of the following is/are the prime considerations in space vehicles and aircraft?
a) High strength-weight ratios for materials and high ratios of payload to the vehicle’s weight
b) High strength-weight ratios for materials only
c) High ratios of payload to vehicles weight only
d) Neither high strength-weight ratios for materials nor high ratios of payload to the vehicle’s weight
Answer: a
Explanation: High strength-weight ratio for materials and high ratios of payload to vehicle weight are the two prime considerations in space vehicles and aircraft.
10. Rusting of high-strength steel due to resident water can cause stress-corrosion and hydrogen embrittlement.
a) False
b) True
Answer: b
Explanation: Rusting of high-strength steel due to resident water can cause stress-corrosion and hydrogen embrittlement. Hydrogen charging of steel during electroplating can cause a brittle fracture.
11. Which of the following is/are the primary materials regarding the construction of aircraft?
a) Aluminum
b) Magnesium and titanium
c) Aluminum, magnesium, titanium, and iron
d) Titanium and magnesium
Answer: c
Explanation: Aluminum, magnesium, titanium, and iron and their alloys are the primary materials regarding the construction of aircraft. These are selected based on a high strength-weight ratio for materials and high ratios of payload to vehicle weight.
12. Which of the following corrosion protective systems is/are included in aircraft industries?
a) Anodizing, cladding and conversion coatings
b) Anodizing and cathodic protection
c) Conversion coatings and anodizing
d) Cathodic protection only
Answer: a
Explanation: Anodizing, cladding, and conversion coatings are the corrosive protective systems used in aircraft industries. Whereas cathodic protection cannot be used in the aircraft industry due to non-conductive electrolytes.
This set of Corrosion Engineering Multiple Choice Questions & Answers focuses on “ Environments – Petroleum Industry”.
1. Which of the following is/are the general areas of the petroleum industry that faces corrosion problems?
a) Production unit
b) Transportation and storage
c) Refinery operations
d) Production unit, transportation, storage, and refinery operations
Answer: d
Explanation: The Petroleum industry is one of the most affected industries with corrosion. The general areas of the petroleum industry that faces corrosion problems are production unit, transportation, storage, and refinery operations.
2. Which of the following impurities is often present in oil and gas wells?
a) Saline water
b) Sulfides
c) Saline water, sulfides and organic impurities such as ammonia
d) Organic impurities such as ammonia
Answer: c
Explanation: Oil and gas fields consumes a tremendous amount of iron and steel pipe, tubing, casings, pumps, and valves. Saline water, sulfides, and organic impurities such as ammonia are the impurities that are usually present in oil and gas fields.
3. How the corrosion characteristics of a well can be determined?
a) Inspection of surface equipment
b) Analysis of carbon dioxide and organic acid
c) Tubing-caliper surveys
d) Inspection of surface equipment, analysis of carbon dioxide, organic acid and tubing-caliper surveys
Answer: d
Explanation: Corrosion characteristics of a well is determined by
i. Inspection of surface equipment
ii. Analysis of carbon dioxide and organic acid
iii. Coupon exposure tests
iv. Tubing-caliper surveys.
4. Which of the following is/are the neutralizers added to well to minimize corrosion?
a) Ammonia and Sodium carbonate
b) Ammonia, sodium carbonate, sodium hydroxide, and sodium silicate
c) Ammonia and sodium silicate
d) Sodium carbonate and sodium silicate
Answer: b
Explanation: Neutralizers that are added to petroleum to minimize corrosion are:
i. Ammonia
ii. Sodium carbonate
iii. Sodium hydroxide
iv. Sodium silicate and some organic inhibitors.
5. Which of the following metals is/are used for petroleum well valves and wellhead parts?
a) Straight chromium stainless steels and stellite
b) Monel and copper-based alloys
c) Monel, straight chromium steels, stellite, and copper-based alloys
d) Monel and stellite
Answer: c
Explanation: Metals that are usually used for petroleum well valves and wellhead parts are straight chromium stainless steels, stellite, monel, and copper-based alloys.
6. Which of the following prevention methods that are usually employed on a beam of offshore drilling?
a) Paints and other organic coatings
b) Cathodic protection with sacrificial anodes or impressed currents
c) Adding inhibitors
d) Adding inhibitors, paints and other organic coatings and cathodic protection
Answer: d
Explanation: Preventions methods that are usually employed on a beam of offshore drilling are:
i. Paints and other organic coatings
ii. Cathodic protection with sacrificial anodes or impressed currents
iii. Adding inhibitors.
7. Which of the following inhibitor has been effective for internal corrosion domestic fuel oil tanks?
a) Alkaline sodium chromate
b) Sodium silicate
c) Ammonia
d) Sodium carbonate
Answer: a
Explanation: Alkaline sodium chromate or sodium nitrate is an effective inhibitor for the corrosion of domestic fuel oil tanks. The chemical formula of sodium chromate is Na 2 CrO 4 .
8. Which of the following impurities that causes corrosion difficulties in refinery operations?
a) Hydrogen sulfide and carbon dioxide
b) Hydrogen sulfide, carbon dioxide, sulfuric acid, and sodium chloride
c) Sodium carbonate and sodium silicate
d) Hydrogen sulfide and sulfuric acid
Answer: b
Explanation: Refinery of crude is done based on the difference in boiling points of the components present and the process is known as fractional distillation. Hydrogen sulfide, carbon dioxide, sulfuric acid, and sodium chloride are the impurities that cause difficulties in refinery operations.
9. Water acts as an electrolyte and causes corrosion as it tends to hydrolyze chlorides and other materials to form an acidic environment.
a) True
b) False
Answer: a
Explanation: Water acts as an electrolyte and causes corrosion in refining operations. This is because water tends to hydrolyze chlorides and other materials to form acidic environments.
10. Which of the following is/are the desalting methods in the petroleum industry?
a) Washing and settling
b) Addition of chemicals such as sulfonates
c) Centrifuging and filtering, washing and settling, the addition of chemicals such as sulfonates
d) Centrifuging and filtering
Answer: c
Explanation: Desalting methods in the petroleum industry are:
i. Washing and settling
ii. Addition of chemicals such as sulfonates
iii. Centrifuging and filtering.
11. Ammonia is used to control the pH of the water and to reduce chloride acidity in the process stream.
a) True
b) False
Answer: a
Explanation: Ammonia is used to control the pH of the water and to reduce chloride acidity in the process streams. It usually maintains a pH of 7 but it damages copper-bearing alloys if the pH becomes 8 or more.
12. Which of the chemical is/are added for the removal of hydrogen sulfide and neutralization?
a) Sodium hydroxide
b) Lime
c) Sodium hydroxide and lime
d) Naphthenic acid
Answer: c
Explanation: Sodium hydroxide and lime are/are added for the removal of hydrogen sulfide and neutralization during the refining of petroleum. NaOH and CaO are the chemical formulae of sodium hydroxide and lime respectively.
13. Which of the following impurity that causes rapid intergranular stress corrosion cracking of sensitized austenitic stainless steels in refinery operations?
a) Sodium chloride
b) Naphthenic acid
c) Hydrogen sulfide
d) Carbon dioxide
Answer: b
Explanation: Naphthenic acid causes rapid intergranular stress corrosion cracking of sensitized austenitic stainless steels in refinery operation. Whereas naphthenic acid is a combination of cyclopentyl and cyclohexyl carboxylic acids.
14. Which of the following metals is/are usually used for heat exchanger tubes carrying water?
a) Carbon steels
b) Brass and cupronickels
c) Arsenical admiralty metal
d) Brass, cupronickels and arsenical admiralty metal
Answer: d
Explanation: Brass, cupronickels, and arsenical admiralty metal are usually used for heat exchangers tubes carrying water. Whereas carbon steels are unsuitable as it rapidly corrodes by the cooling water.
Answer: a
Explanation: Chromium is the most beneficial alloying element in steel for resistance to sulfur compounds. As per the study, 2.25% chromium and 1% molybdenum is required for less than 0.2% H 2 S in the gas.
Sanfoundry Global Education & Learning Series – Corrosion Engineering.
This set of Corrosion Engineering Multiple Choice Questions & Answers focuses on “Environments – Biological Corrosion”.
1. Biological corrosion is a deterioration of a metal by the corrosion process that occurs directly or indirectly due to the activity of living organisms.
a) True
b) False
Answer: a
Explanation: Biological corrosion is a deterioration of a metal by the corrosion process that occurs directly or indirectly due to the activity of living organisms. This includes micro and microorganism.
2. Which of the following environments in which the biological activity may influence corrosion?
a) Soil
b) Fresh and seawater
c) Petroleum products
d) Soil, freshwater, seawater and petroleum products
Answer: d
Explanation: Biological activity will influence the corrosion of materials in a variety of environments including soil, freshwater, seawater, and petroleum products. These living organisms are sustained by chemical reactions.
3. Which of the following is/are the processes that affect the corrosion behavior of metals by biological activity?
a) By influencing anodic and cathodic reactions
b) By influencing protective surface films
c) By producing deposits, by influencing anodic, cathodic reactions and protective surface films
d) By creating non-corrosive conditions
Answer: c
Explanation: The process that affects the corrosion behavior of metals by biological activity are:
i. By directly influencing anodic and cathodic reactions
ii. By influencing protective surface films
iii. By creating a corrosive environment
iv. By producing deposits.
4. Which of the following component is taken into account to classify aerobic and anaerobic organisms?
a) Nitrogen
b) Oxygen
c) Argon
d) Phosphorus
Answer: b
Explanation: Percentage or relative amount of oxygen in the environment is taken into account to classify the microorganisms into aerobic and aerobic bacteria. The anaerobic attack is pre-dominate in underground corrosion due to the non-availability of oxygen.
5. Which of the following organisms are regarded as microorganisms?
a) Bacteria
b) Fungi
c) Protozoa
d) Bacteria, fungi, protozoa, and nematodes
Answer: d
Explanation: Bacteria, fungi, protozoa, and nematodes are one of the microorganisms usually present in the soil. Biological activity that directly or indirectly affects the corrosion of metals is known as biological corrosion.
6. Which of the following anaerobic bacteria that influence the corrosion behavior of buried steel structures?
a) Sulfur-reducing bacteria
b) Sulfur-oxidizing bacteria
c) Thiobacillus thiooxidans
d) Sulfur-reducing and sulfur-oxidizing bacteria
Answer: a
Explanation: Sulfur-reducing anaerobic bacteria influences the corrosion behavior of buried steel structures. SO 4 -2 +4H 2 ==>S -2 +4H 2 O is the general chemical reaction of sulfur-reducing anaerobic bacteria.
7. Thiobacillusthiooxidans are the type of aerobic bacteria that are capable of oxidizing sulfur-bearing compounds to sulfuric acid.
a) False
b) True
Answer: b
Explanation: Thiobacillusthiooxidans are the type of aerobic bacteria that are capable of oxidizing elemental sulfur and sulfur-bearing compounds to sulfuric acid. 2S+3O 2 +2H 2 O==>2H 2 SO 4 is the general chemical reaction of sulfur-oxidizing bacteria.
8. Which of the following coatings is/are used for the prevention of microbiological corrosion in buried steel?
a) Asphalt
b) Enamel
c) Plastic tape
d) Asphalt, enamel and plastic tape
Answer: d
Explanation: Microbiological corrosion influences the corrosion of buried steel structures in soil. This can be prevented by coatings such as asphalt, enamel, and plastic tape.
9. Which of the following is/are the preventions of microbiological corrosion in soil?
a) Use of substitute materials
b) Use of inhibitors
c) Applying coatings, use of inhibitors, cathodic protection and substitute materials
d) Cathodic protection
Answer: c
Explanation: Preventions to microbiological corrosion in soil:
i. Use of substitute materials such as asbestos and plastic
ii. Use of coatings such as asphalts and enamel
iii. Use of inhibitors and germicides
iv. Cathodic protection can be applied.
10. Which of the following acids are produced by microorganisms such as fungus and mold?
a) Oxalic acid
b) Lactic acid
c) Acetic acid
d) Oxalic acid, lactic acid, acetic acid, and citric acid
Answer: d
Explanation: Macroorganisms such as fungus and mold are also capable of influencing corrosion of metals in many environments. They assimilate organic matter and can produce considerable amounts of acids such as oxalic acid, lactic acid, acetic acid, and citric acid.
11. Which of the following materials is/are usually attacked by fungus?
a) leathers
b) Rubbers
c) Leathers, rubbers and bare and coated metals
d) Bare and coated metals
Answer: c
Explanation: Materials that are usually attacked by fungus are leathers, rubbers, and bare and coated metals. Though the attack of fungus on materials may not affect many mechanical properties it deteriorates the appearance of materials.
12. Which of the following is/are the preventions for the growth of mold on metal surfaces?
a) Periodic cleaning and storing in the high humid atmosphere
b) Periodic cleaning, reducing relative humidity during storage and applying toxic organic agents
c) Reducing relative humidity during storage and applying toxic organic agents
d) Periodic cleaning and reducing relative humidity during storage
Answer: b
Explanation: Preventions for the growth of mold on metal surfaces are:
i. Periodic cleaning of metal surfaces
ii. Reducing relative humidity during storage
iii. Applying toxic organic agents.
Answer: a
Explanation: Aqueous organisms such as barnacles, mussels, and algae influence the corrosion of metals in water. This includes an increase in the requirement of power for a severely fouled ship and limits heat transfers in heat exchangers.
Sanfoundry Global Education & Learning Series – Corrosion Engineering.
This set of Corrosion Engineering written test Questions & Answers focuses on “Environments – Liquid Metals and Fused Salts”.
1.The liquid-metal corrosion is usually a physical effect rather than an electrochemical attack.
a) True
b) False
Answer: a
Explanation: Liquid metal corrosion is usually a physical effect rather than an electrochemical attack. Electrochemical attack includes reduction and oxidation of hydrogen ions and metallic atoms respectively.
2. Which of the following is/are the types of liquid-metal corrosion?
a) Solution of structural metal
b) Diffusion of liquid into solid metal
c) Intermetallic compound formation
d) Solution of structural metal, diffusion of liquid into solid metal and intermetallic compound formation
Answer: d
Explanation: Types of liquid-metal corrosion are:
i. Solution of structural metal
ii. Diffusion of liquid into solid metal
iii. Intermetallic compound formation
iv. Mass transfer.
3. Which of the following is/are undesirable in heat-exchange systems handling liquid metals?
a) Deposition of impurities in cool areas
b) Resistance to heat transfer
c) Formation of brittle intermetallic compounds, resistance to heat transfer and deposition of impurities in cool areas
d) Formation of brittle intermetallic compounds
Answer: c
Explanation: Conditions that are undesirable in heat-exchange systems handling liquid metals:
i. Deposition of impurities in cool areas
ii. Resistance to heat transfer
iii. Formation of brittle intermetallic compounds.
4. Which of the following parameter has a direct relation with the corrosion rate in liquid metals?
a) Percentage of alloying elements
b) Solubility of the metallic structure in liquid metal
c) Solubility of alloying elements in metallic matrix
d) Percentage of oxygen
Answer: b
Explanation: Solubility of alloying elements in metallic matrix has direct relation with corrosion rate in liquid metals. Whereas liquid-metal corrosion is a physical effect rather than a chemical effect.
5. Which of the following parameter is taken as Xin the given graph regarding corrosion of various metals in liquid-metal corrosion?
a) Atomic weight
b) Weight loss
c) Solubility percentage
d) Atomic number
Answer: c
Explanation: The given graph shows the direct relation of corrosion rate with solubility of metallic structures in liquid mercury for various metals. And solubility of the metallic component in liquid mercury is taken as x.
6. Which of the following materials shows good resistance to both liquid-metals and high-temperature oxidation?
a) High alloy stainless steels
b) Monel
c) Hastelloy
d) Hastelloy, high alloy stainless steels and monel
Answer: d
Explanation: Materials that show good resistance to both liquid-metals and high-temperature oxidation are 18Cr-8Ni stainless steel, high alloy stainless steel, monel, and Hastelloy.
7. Which of the following type of stainless steels are attacked by magnesium at its melting point?
a) Duplex stainless steels
b) Austenitic stainless steels
c) Martensitic stainless steels
d) Ferritic stainless steels
Answer: b
Explanation: Austenitic stainless steels are the types of stainless steels that are attacked by magnesium at its melting. Liquid magnesium preferentially leaches out nickel from this alloy from the iron matrix.
8. The presence of traces of titanium and magnesium in mercury can inhibit the corrosion of iron in ferrous-based alloys.
a) True
b) False
Answer: a
Explanation: Traces of titanium and magnesium in mercury can inhibit the corrosion of iron in ferrous-based alloys. And it is reliable to use carbon steel in mercury for up to 540°C.
9. Which of the following materials have superior corrosion resistance and high rupture strength in mercury?
a) 5% chromium steels
b) Si-Cr-Mo steels
c) 5% chromium steels and Si-Cr-Mo steels
d) Carbon steels
Answer: c
Explanation: Now-a-days 5% chromium steels and Si-Cr-Mo steels replace carbon steels in mercury due to its superior corrosion resistance and high rupture strength.
10. Which of the following type of corrosion Is usually encounters for various materials in liquid metal environment?
a) Uniform corrosion
b) Stress cracking corrosion
c) Crevice corrosion
d) Pitting corrosion
Answer: b
Explanation: Stress cracking corrosion is a type of corrosion that usually encountered in various materials in a liquid metal environment. This is due to the chemisorption of liquid-metal atoms and a reduction in tensile strength at the crack tip.
11. Which of the following alloys is/are usually used for sodium hydroxide fused salt?
a) Nickel-based alloys
b) Copper-based alloys
c) Ferrous alloys
d) Zinc based alloys
Answer: a
Explanation: Sodium hydroxide is the most commonly used fused salt. And nickel-based alloys show good corrosion resistance to sodium hydroxide environment.
12. Which of the following is/are the types of mass transfer due to liquid-metal corrosion?
a) Composition-gradient mass transfer
b) Thermal-gradient mass transfer
c) Neither composition nor thermal gradient mass transfer
d) Both composition and thermal gradient mass transfer
Answer: d
Explanation: Types of mass transfer due to liquid-metal corrosion are:
i. Composition-gradient mass transfer
ii. Thermal-gradient mass transfer.
13. Which of the following types of steel coatings is/are preferred for automobile body parts?
a) Galvanized steels
b) Electroplated steels
c) Galvanized steels, electroplated steels and complete immersion of corrosion preventing primer coat
d) Complete immersion of corrosion preventing primer coat
Answer: c
Explanation: Types of steel coatings that are preferred for automobile parts are:
i. Galvanized steels
ii. Electroplated steels
iii. Complete immersion of corrosion preventing primer coat.
Answer: d
Explanation: Preventive measures to minimize automobile corrosion are:
i. Use of inhibitor in the engine cooling system
ii. Avoid very short runs
iii. Fill the gasoline tank at least half full.
Sanfoundry Global Education & Learning Series – Corrosion Engineering.
This set of Corrosion Engineering Multiple Choice Questions & Answers focuses on “Modern Theory Principles – Thermodynamics – 1”.
1. Which of the following is/are the applications of modern electrode kinetic principles?
a) Anodic protection
b) Noble metal alloying
c) Methods to measure corrosion rates rapidly
d) Anodic protection, noble metal alloying and methods to measure corrosion rates rapidly
Answer: d
Explanation: Modern electrode kinetics deals with electrochemical corrosion of aqueous solution and it results in the applications of
Anodic protection
Noble metal alloying
Methods to measure corrosion rates rapidly.
2. What is the direct measure of work capacity or electrical energy available from a system?
a) Change in enthalpy
b) Change in Gibbs free energy
c) Reaction time
d) Concentration of reactants
Answer: b
Explanation: Change is Gibbs free energy is the difference of free energies of the reaction products and reactants. And it is a direct measure of the work capacity or maximum electrical energy available in from a system.
3. If the transition of a system from one state to another state resulted in negative free energy change then it is known as a spontaneous reaction.
a) True
b) False
Answer: a
Explanation: If the transition of a system from one state to another state resulted in negative free energy change then it is known as a spontaneous reaction. It means the free energy of products is less than the free energy of reactants.
4. Which of the following is true, if the transition of a system results in positive Gibbs free energy change?
a) It is a spontaneous reaction
b) Free energy of products is less
c) It is a non-spontaneous reaction
d) Free energy of reactants is more
Answer: c
Explanation: If the transition of a system from one state to another state resulted in positive free energy change then it is known as a non-spontaneous reaction. It means the free energy of reactants is less than the free energy of products. It requires external heat or force to proceeds with the reaction.
5. Which of the following is a spontaneous reaction?
a) Production of ammonia
b) Corrosion of metals
c) Photosynthesis reaction
d) Generation of oxygen from water
Answer: b
Explanation: Spontaneous reaction is a reaction in which the reactants convert into products without any supply of external energy. Oxidation of metal atoms into metal ions due to the instability of metallic atoms is known as the corrosion of metals.
6. The change in Gibbs free energy is a path function and it is independent of the state of the system.
a) False
b) True
Answer: a
Explanation: The change in Gibbs free energy is a state function and it is independent of the path followed by the system to reach that state. It is denoted by ΔG .
7. Which of the following formula is used to calculate the Gibbs free energy of an electrochemical reaction?
a) ΔG=-nFE 0 cell
b) ΔG=+nFE 0 cell
c) ΔG=-nFE cell
d) ΔG=+nFE cell
Answer: c
Explanation: ΔG=-nFE cell where n is the electrons participated in the reaction, F is the faraday constant , E cell is the overall cell potential and E 0 cell is the standard cell potential.
8. What is the change in Gibb’s free energy of a Cu-Zn system with a cell potential of 1.10V?
a) -11.13 KJ/mol
b) +21.23 KJ/mol
c) +11.13 KJ/mol
d) -21.23 KJ/mol
Answer: d
Explanation: Given, Cell potential = 1.10V
n=number of electrons involved in reaction = 2
F=96500 coulombs
We know, ΔG=-nFE cell
ΔG=-2*96500*1.10
ΔG=-21.23 KJ/mol
9. Which of the following is/are correct regarding the given figure?
a) It is a reversible cell with unit activity
b) Copper and zinc are cathode and anode respectively
c) It is a reversible cell of Cu-Zn system with standard cell potential of 1.10V, copper and zinc are cathode and anode respectively
d) The standard cell potential is 1.10V
Answer: c
Explanation: Given figure represents a Cu-Zn system with standard cell potential of 1.10V. Copper and Zinc are cathode and anode respectively. Whereas two half-cells are separated by a porous membrane.
10. What are the cathodic and anodic reactions respectively of a given Cu-Zn system?
a) Cu==>Cu +2 +2e and Zn +2 +2e==>Zn
b) Cu +2 +2e==>Cu and Zn==>Zn +2 +2e
c) Cu==>Cu +2 +2e and 2Zn +1 +2e==>2Zn
d) Cu +2 +2e==>Cu and 2Zn==>2Zn +1 +2e
Answer: b
Explanation: As the standard hydrogen potential of copper is relatively higher than standard hydrogen potential of zinc it acts as cathode and zinc act as anode.
Cathodic reaction is Cu +2 +2e==>Cu
Anodic reaction is Zn==>Zn +2 +2e
11. What is the overall standard cell potential of a given Cu-Fe system?
a) +0.78V
b) -0.14V
c) -0.78V
d) +0.14
Answer: a
Explanation: In Cu-Fe system, copper (E 0 =+0.34V) acts as cathode and iron will acts as anode (E 0 =-0.44V). Standard cell potential of a system can be calculated using E 0 cell =E 0 cathode –E 0 anode . Therefore, overall standard cell potential of given Cu-Fe system is 0.34 – = 0.78V.
12. Which of the following metal is used as a solid interface for hydrogen gas in the standard hydrogen electrode?
a) Copper
b) Zinc
c) Gold
d) Platinized platinum
Answer: d
Explanation: Platinized platinum metal is used as the solid interface for hydrogen gas in the standard hydrogen electrode. It is due to the inertness of the metal and ease with which electron transfer occurs on its surface. Platinized platinum is black platinum-coated platinum.
Answer: a
Explanation: Nernst equation for given chemical reaction nA + mB ==> pC + qD is E=E 0 +2.3log{([A] n +[B] m )/([C] p +[D] q )} where A and B are reactants, C and D are products and m,n,p and q are the number of moles respectively.
Sanfoundry Global Education & Learning Series – Corrosion Engineering.
This set of Corrosion Engineering Objective Questions & Answers focuses on “Modern Theory Principles – Thermodynamics – 2”.
1. Which of the following is a cathode and anode respectively in the Ag-Fe system?
a) Iron and Silver
b) Silver and Iron
c) Gold and Iron
d) Iron and Gold
Answer: b
Explanation: In the Ag-Fe system, Silver acts as a cathode as the standard hydrogen potential is relatively higher than the Iron and Iron acts as anode due to relatively less standard hydrogen potential.
2. An electrochemical reaction is always a combination of oxidation half-cell and a reduction of half-cell.
a) True
b) False
Answer: a
Explanation: Corrosion is usually an electrochemical process which is a combination of oxidation half-cell and reduction half-cell. Oxidation and reduction reactions are simultaneous in nature and it is also called Redox reactions.
3. What is the cathodic and anodic reactions respectively of Cu-Ag system?
a) Ag==>Ag +2 +2e and Cu +2 +2e==>Cu
b) Cu==>Cu +2 +2e and Ag==>Ag +2 +2e
c) 2Ag +1 +2e==>2Ag and Cu==>Cu +2 +2e
d) 2Ag==>2Ag +1 +2e and Cu +2 +2e==>Cu
Answer: c
Explanation: Standard hydrogen potential of silver is +0.80V and copper is +0.34V.
Cathodic reaction: 2Ag +1 +2e==>2Ag
Anodic reaction: Cu==>Cu +2 +2e
4. Which of the following type of reaction is shown in the given figure?
a) Non-spontaneous reaction
b) Equilibrium reaction
c) Neither spontaneous nor non-spontaneous reaction
d) Spontaneous reaction
Answer: d
Explanation: Spontaneous reaction is a reaction in which the change in Gibbs free energy is negative. It means the free energy of reactants is more than the free energy of products.
5. Which of the following diagrams shows the stability of metals over a range of pH and potential of a system?
a) Phase diagrams
b) Pourbaix diagrams
c) Phase diagrams and Pourbaix diagrams
d) Colling curves
Answer: b
Explanation: Pourbaix diagrams show the stability of metal over a range of pH and potential of a system. It also includes native zone, passive zone, and corrosive zone. It is also called as potential-pH diagrams.
6. What is depicted in the given figure?
a) Phase diagram of the Fe-C system
b) Pourbaix diagram for Fe-O 2 system
c) Pourbaix diagram for Fe-H 2 O system
d) Colling curve pure iron
Answer: c
Explanation: Pourbaix diagram is a diagram that shows the stability of species of a metal over a range of pH and potential of a system. Given figures represents the pourbaix diagram of the Fe-H 2 O system.
7. Which of the following zone of given Pourbaix diagram indicates the immune zone?
a) Zone 1
b) Zone 2
c) Zone 3
d) Zone 4
Answer: a
Explanation: The Immune zone is the zone of the pourbaix diagram in which the stability of native metal in zero oxidation state is high. It is the zone in which no corrosion or passivation takes place.
8. Which of the following zone of given Pourbaix diagrams indicate a passive zone?
a) Zone 1 and 2
b) Zone 2 and 3
c) Zone 2, 3 and 6
d) Zone 4 and 5
Answer: d
Explanation: Passive zone is the zone in the pourbaix diagram in which the passivation of metal takes place. It is the operating zone in various industries to minimize corrosion and to increase the efficiency of the process.
9. Which of the following is/are the applications of Pourbaix diagrams?
a) Predicting the spontaneous direction of reactions
b) To reduce corrosion attack
c) To reduce corrosion attack, to predict the direction of spontaneous reaction and to estimate the composition of corrosion product
d) To estimate the composition of corrosion product
Answer: c
Explanation: Applications of Pourbaix diagrams:
i. Predicting the spontaneous direction of reactions
ii. To reduce corrosion attack
iii. To estimate the composition of corrosion product.
10. Which of the following is/are the limitations of Pourbaix diagrams?
a) Rate of reaction is can’t be predicted
b) It neglects the impurities of working conditions
c) Stability of metallic species is predicted
d) Rate of reaction is not predicted and it neglects the impurities of working conditions
Answer: d
Explanation: Limitations of Pourbaix diagrams:
i. Rate of reaction can’t be predicted
ii. It neglects the impurities of working conditions
iii. Alloying elements of alloys are also neglected.
This set of Corrosion Engineering Multiple Choice Questions & Answers focuses on “Modern Theory Principles – Polarization – 1”.
1. What is meant by an anode?
a) An electrode at which reduction process takes place
b) An electrode at which oxidation process takes place
c) An electrode at which neither the oxidation nor reduction takes place
d) An electrode at which both oxidation and reduction takes place
Answer: b
Explanation: An electrode at which the oxidation process takes place is known as anode whereas the electrode at which reduction process takes place is known as the cathode.
2. Which of the following is correct regarding Polarization?
a) It is the deviation from equilibrium potential
b) It results from the change in net current flow
c) Magnitude is measured in terms of overvoltage
d) It is the deviation from equilibrium potential that occurred due to the change in net current flow and its magnitude is measured in terms of overvoltage.
Answer: d
Explanation: Polarization is the deviation from equilibrium potential that occurred due to the change in net current flow and its magnitude is measured in terms of overvoltage.
3. What is the symbol of overvoltage?
a) Alpha
b) Beta
c) Eta
d) Delta
Answer: c
Explanation: The magnitude of polarization is measured in terms of over voltage and it is denoted with symbol Eta . It is the difference of corrosion potential (E corr ) and the standard potential of an electrode.
4. Exchange current density is the current per unit area of either oxidation or reduction process at the equilibrium.
a) True
b) False
Answer: a
Explanation: Exchange current density is the current per unit area of either oxidation or reduction process at the equilibrium. Type of metal and environment are the factors of exchange current density and it is denoted by i 0 .
5. What is the formula to calculate rate of oxidation or rate of reduction during equilibrium?
a) r 0 =r R =i 0 nF
b) r 0 =r R =i 0 /nF
c) r 0 =r R =i 0 n/F
d) r 0 =r R =nF/i 0
Answer: b
Explanation: Equilibrium is defined as the state at which rate of oxidation is equal to the rate of reduction. And the formula to calculate rate of oxidation or reduction is r 0 =r R =i 0 /nF where i 0 is exchange current density, n is number of electrons involved and F is faraday’s constant.
6. Which of the following metal shows the highest exchange current density for hydrogen-hydrogen ion as per given figure?
a) Mercury
b) Iron
c) Platinized platinum
d) Platinum
Answer: c
Explanation: Platinized platinum shows the highest exchange current density for hydrogen-hydrogen ion due to its high inertness and electrically conductivity. The order follows as (i 0 ) Pt H+/H2 >(i 0 ) Fe H+/H2 >(i 0 ) Hg H+/H2 .
7. Which of the following is the controlling factor of Activation polarization?
a) The activation energy of a reaction
b) Diffusion of ions in the solution
c) The temperature of a solution
d) The velocity of a solution
Answer: a
Explanation: Activation polarization is the mechanism of polarization that depends on the activation energy of a reaction. Activation energy is the minimum energy required for reacting species to undergo chemical reactions.
8. Which of the following mentioned is/are the types of polarization?
a) Activation polarization
b) Concentration polarization
c) Resistance polarization
d) Activation, concentration and resistance polarization
Answer: d
Explanation: Types of polarization:
Activation polarization
Concentration polarization
Resistance polarization.
9. What is the relationship between reaction rate and overvoltage for activation polarization?
a) n a =±Î˛log(i 0 /i)
b) n a =±Î˛log(I/i 0 )
c) n a =±Î˛log(1-i 0 /i)
d) n a =±Î˛log(1-i/i 0 )
Answer: b
Explanation: The relationship between reaction rate and overvoltage for activation polarization can be noted as n a =±Î˛log(I/i 0 ) where β is a Tafel constant and i 0 is exchange current density.
10. What is depicted in the given figure?
a) Concentration polarization of hydrogen-hydrogen ion
b) Resistance polarization of hydrogen-hydrogen ion
c) Activation polarization of hydrogen-hydrogen ion
d) Both activation and concentration polarization of hydrogen-hydrogen ion
Answer: c
Explanation: The given figure depicts the activation polarization of the hydrogen-hydrogen ion electrode. Curve1 indicates the cathodic polarization whereas curve2 indicates the anodic polarization.
This set of Corrosion Engineering Questions & Answers for Exams focuses on “Modern Theory Principles – Polarization – 2”.
1. Which of the following is/are correct regarding concentration polarization?
a) Diffusion of ions in the bulk solution is the controlling factor
b) It usually operates at a high current density
c) It is a continuation of Activation polarization
d) It is a continuation of activation polarization, diffusion of ions in the bulk solution is the controlling factor and it usually operates at high current densities
Answer: d
Explanation: Concentration polarization is the mechanism of polarization in which diffusion of ions in the bulk solution is the controlling factor, it is a continuation of activation polarization and it usually operates at high current densities.
2. What is depicted in the given figure?
a) Activation polarization
b) Concentration polarization
c) Resistance polarization
d) Activation and concentration polarization
Answer: b
Explanation: The given figure depicts the concentration polarization of a reaction. It is the mechanism of polarization in which the diffusion of ions in the bulk solution is the controlling factor. It usually encounters at high-density currents and low concentration solution.
3. What is the formula to determine limiting diffusion current density (i L ) of concentration polarization?
a) i L =xnFC B /D
b) i L =DC B /nFx
c) i L =DnFC B /x
d) i L =x/DnFC B
Answer: c
Explanation: i L =DnFC B /x is the formula to determine the limiting diffusion current density (i L ) of concentration polarization. Where I L is the limiting diffusion current density, D is the diffusion coefficient, C B concentration of ions in bulk solution and x is the thickness of diffusion layer.
4. Agitation will increase the limiting diffusion current density of concentration polarization.
a) True
b) False
Answer: a
Explanation: Agitation tends to decrease the thickness of the diffusion layer by supply enough ions to the metal interface hence there will be an increase in limiting diffusion current density of concentration polarization.
5. Which of the following is/are correct regarding the given figure?
a) Velocity, temperature, and concentration are the factors that influence limiting current density
b) Limiting current density decreases with an increase in velocity, temperature, and concentration
c) Limiting current density increase with the increase in velocity, temperature, and concentration
d) Velocity, temperature, and concentration are the factors that influence limiting current density and it increases as it increases
Answer: d
Explanation: The given figure shows the increase in limiting diffusion current density of concentration polarization with an increase in velocity, temperature, or concentration. It is due to the relatively high availability of reacting species at the interface and decrease in thickness of the diffusion layer.
6. Which of the following type of polarization is depicted in the given figure?
a) Activation polarization
b) Concentration polarization
c) Activation and concentration polarization
d) Resistance polarization
Answer: c
Explanation: The given figure depicts the cathodic polarization of an element with activation and concentration polarizations. Concentration polarization is the continuation of activation polarization at higher current densities.
7. Which of the following is/are correct regarding resistance polarization?
a) Activation energy at the interface is the controlling factor
b) The resistance of transition between electrodes and electrolytes
c) Diffusion of ions in the bulk solution is the controlling factor
d) The resistance of reacting ions for diffusion is the controlling factor
Answer: b
Explanation: Resistance polarization is the type of polarization in which there is a resistance of transition between electrodes and electrolytes. But this polarization has a negligible effect on corrosion kinetics.
8. Which two scientists present the first formal presentation on mixed potential theory?
a) Wagner and Traud
b) Wagner and Evans
c) Traud and Nernst
d) Wilsmore and Nernst
Answer: d
Explanation: Mixed potential theory is the electrochemical hypothesis of modern corrosion presented by Wagner and Traud in the year 1938. It relates the potentials and currents of the corrosion system to determine corrosion potential (E corr ) and corrosion current (i corr ).
9. Which of the following is/are the hypothesis of mixed potential theory?
a) Any electrochemical reaction can be divided into two or more partial reactions
b) No net accumulation of electric charge during the reaction
c) Any electrochemical reaction can be divided into two or more partial reactions and no net accumulation of electric charge during the reaction
d) Electrochemical reactions can’t be divided into partial reactions
Answer: c
Explanation: Hypothesis of mixed potential theory:
i. Any electrochemical reactions can be divided into two or more partial reactions
ii. No net accumulation of electric charge during the reaction.
10. Which of the following is depicted in the given mixed potential schematic?
a) Dissolution of zinc
b) Oxidation of hydrogen
c) Reduction of zinc
d) Dissolution of copper
Answer: a
Explanation: The given mixed potential schematic depicts the dissolution of zinc. It shows the anodic polarization of zinc, cathodic polarization of hydrogen, and resulting in E corr and i corr .
This set of Corrosion Engineering Multiple Choice Questions & Answers focuses on “Modern Theory Principles – Passivity”.
1. Which of the following is/are correct regarding passivation?
a) It is defined as the loss of reactivity at certain conditions
b) Usually results in the formation of the oxide layer
c) The corrosion rates are relatively low
d) It is defined as loss of reactivity at certain conditions usually due to the formation of the oxide layer and corrosion rates are relatively low
Answer: d
Explanation: Passivation is defined as the loss of reactivity of metals/alloys at certain conditions usually due to the formation of the oxide layer and corrosion rates are relatively low.
2. The passive state of a metal is often relatively unstable and subject to damage.
a) True
b) False
Answer: a
Explanation: Passivation is the loss of chemical reactivity of a metal due to the formation of the oxide layer. It is relatively unstable and subject to damage. Chemical properties, wear resistance and thickness are the factors for the stability of the passive layer.
3. Which of the following is/are the metal/alloys that demonstrate active-passive transitions?
a) Iron and stainless steels
b) Nickel and its alloys
c) Iron, stainless steels, nickels, titanium, and its alloys
d) Titanium and its alloys
Answer: c
Explanation: Metals/alloys that demonstrate active-passive transitions is/are:
Iron and stainless steels
Nickel and its alloys
Titanium and its alloys
Chromium
Aluminum and its alloys.
4. What is depicted in the given polarization curve?
a) Cathodic dissolution of typical active-passive transition metal
b) Anodic dissolution of typical active-passive transition metal
c) Anodic dissolution of a metal
d) Cathodic dissolution of a metal
Answer: b
Explanation: Given the polarization curve, depicts the typical anodic dissolution of active-passive transition metal. It includes an active region, passive region, and trans passive region.
5. Which of the following is/are correct regarding the active region of metals?
a) Corrosion rates increase exponentially
b) Corrosion rates increase linearly
c) It follows typical Tafel behavior
d) It follows typical Tafel behavior and corrosion rates increases exponentially
Answer: d
Explanation: Active region is the first stage of active-passive transition in which the corrosion rates increase exponentially and it follows typical Tafel behavior.
6. The Trans passive region is the region in which the corrosion rate increases with an increase in potential.
a) True
b) False
Answer: a
Explanation: Trans passive region is the last region of active-passive transitions of metal in which the corrosion rate increases with an increase in potential. It is formed due to the instability of the passive layer at that high potentials.
7. Which of the following is/are the important characteristics of active-passive transitions of a metal?
a) Passive potential (E pp )
b) Critical anodic current density (i c )
c) Passive potential (E pp ) and Critical anodic current density (i c )
d) Neither passive potential nor critical anodic current density
Answer: c
Explanation: Passive potential is defined as the potential of a system at which the passivation of metal is starts whereas critical anodic current density is defined as the current density at which passivation of metals starts.
8. Which of the following statements is/are correct regarding the given schematic?
a) Increase in acid concentration and temperature increase the passive potential
b) Increase in acid concentration and temperature increase critical current density
c) The relative reduction in the size of the passive region
d) Increase in acid concentration and temperature increase critical current density, passive potential and we can observe a relative reduction in the size of the passive region
Answer: d
Explanation: Statements that are correct regarding the given schematic are:
Increase in acid concentration and temperature increase the passive potential
Increase in acid concentration and temperature increase critical current density
The relative reduction in the size of the passive region.
9. Which of the following metal doesn’t possess a trans passive region?
a) Iron
b) Titanium
c) Nickel
d) Aluminum
Answer: b
Explanation: Typical active-passive transitions metals possess active region, passive region, and trans passive region. Whereas titanium doesn’t possess trans passive region is due to the formation of a more protective titanium oxide film structure.
10. Which of the following metals/alloys passivates spontaneously in acid solutions containing oxidizers or dissolved oxygen?
a) Copper
b) Titanium
c) Stainless steels and titanium
d) Nickel
Answer: b
Explanation: Stainless steels and titanium passivates spontaneously in acid solutions containing oxidizers or dissolved oxygen. A decrease in passive potential and critical current density is the driving force for the spontaneous passivation.
This set of Corrosion Engineering Questions and Answers for Aptitude test focuses on “Modern Theory Applications – Predicting Corrosion Behavior”.
1. Which of the following is/are the applications of mixed-potential theory?
a) Permit prediction of complex corrosion behavior
b) To develop new corrosion prevention methods
c) To develop new rapid corrosion rate measurement
d) Permit prediction of complex corrosion behavior, to develop new corrosion prevention methods and to develop new rapid corrosion rate measurement
Answer: d
Explanation: Applications of the mixed-potential theory are:
Permit prediction of complex corrosion behavior
To develop new corrosion prevention methods
To develop new rapid corrosion rate measurement.
2. Which of the following is/are correct when oxidizing agents are added to a corrosion system containing a non-passivating metal?
a) Rate of corrosion decreases after certain potential
b) Rate of corrosion increases with increase in oxidizers concentration
c) Rate of corrosion increases after certain potential
d) Results in the formation stable oxide layer
Answer: b
Explanation: The rate of corrosion increases with increase as the concentration of oxidizing agents containing non-passivating metal. It is due to the reduction of oxygen on the surface of the metal and due to the absence of an oxide layer.
3. Which of the following is described in the given figure?
a) Effect of oxidizers concentration on cathodic behavior of active metal
b) Effect of oxidizers concentration on the electrochemical behavior of active metal
c) Effect of oxidizers concentration on the electrochemical behavior of active-passive transition metal
d) Effect of oxidizers concentration on cathodic behavior of active-passive transition metal
Answer: c
Explanation: The given figure describes the effect of oxidizers concentration on the electrochemical behavior of active-passive transition metal. The rate of oxygen reduction varies with oxidizer concentration and the corresponding rate of metallic dissolution varies.
4. What is the potential of oxidizers at which metal passivation starts according to a given figure?
a) Concentration corresponding to C
b) Concentration corresponding to D
c) Concentration corresponding to A
d) Concentration corresponding to B
Answer: a
Explanation: Given the figure describes the effect of oxidizer concentration on the electrochemical behavior of active-passive transition metal. Passivation of metal starts at the oxidizer’s concentration corresponding to point C.
5. Which of the following is described in the given figure?
a) Effect of velocity on anodic dissolution of oxygen
b) Effect of velocity on the electrochemical behavior of active-passive transition metal
c) Effect of velocity on the electrochemical behavior of a normal metal
d) Effect of velocity on the cathodic dissolution of metal
Answer: c
Explanation: The given figure depicts the effect of velocity on the electrochemical behavior of a normal metal. Here metallic dissolution is anodic reaction and reduction of oxygen is a cathodic reaction.
6. The corrosion rate is usually dependent at low velocity whereas at high velocities it becomes independent.
a) True
b) False
Answer: a
Explanation: Corrosion rate is usually dependent at low velocities whereas at high velocities it becomes independent. It is due to enough availability of ions at the interface and thereby it depends on activation energy.
7. Which of the following type of polarization has a negligible effect on velocity?
a) Concentration polarization
b) Activation polarization
c) Concentration polarization and Activation polarization
d) Neither concentration nor Activation polarization
Answer: b
Explanation: Activation polarization is the mechanism of polarization in which the activation energy of reactants at the interface is the driving force. It has a negligible effect on velocity as it is independent of diffusion of ions in the bulk solution.
8. Which of the following is depicted in the given figure?
a) Galvanic effect of copper-platinum
b) Corrosion of platinum
c) Corrosion of Zinc
d) Galvanic effect of zinc-platinum
Answer: d
Explanation: The given figure depicts the galvanic effect of zinc-platinum. Corrosion of zinc increases preferentially as the total rate of hydrogen evolution increases on zinc and platinum.
9. Severe corrosion of metals occurred when coupled with platinum is due to the higher current density for hydrogen evolution but not due to the reversible potential of the platinum-platinum ion electrode.
a) True
b) False
Answer: a
Explanation: Severe corrosion of metals occurred when coupled with platinum is due to the higher current density for evolution but not due to the reversible potential of the platinum-platinum ion electrode. Notably, platinized platinum has the highest exchange current density for hydrogen evolution.
10. The reversible potential of gold is more positive than platinum in emf series whereas in galvanic series the position of gold is below platinum.
a) False
b) True
Answer: b
Explanation: The reversible potential of gold is more positive than platinum in emf series whereas in galvanic series the position of gold is below platinum. It is due to the exchange current density of hydrogen evolution, as the galvanic tests are usually conducted in an acidic environment.
11. Which of the following is depicted in the given figure?
a) Galvanic effect of the zinc-platinum couple
b) Effect of the velocity of zinc-platinum couple
c) Effect of the cathode-anode area ratio of a zinc-platinum couple
d) Effect of oxidizers on the zinc-platinum couple
Answer: c
Explanation: The given figure depicts the effect of the cathode-anode area ratio of the zinc-platinum couple. The exchange current density of hydrogen evolution on platinum (10cm 2 ) is more than the current density of platinum (1cm 2 ).
12. In a galvanic couple, the corrosion rate of the metal with active corrosion potential is accelerated whereas the corrosion rate of noble metal retards preferentially.
a) True
b) False
Answer: a
Explanation: In a galvanic couple, one metal acts as the anode , and its corrosion rate is accelerated whereas other acts as the cathode and its corrosion rate are retards preferentially.
13. Which of the following metals that are spontaneously passivated on coupling with platinum?
a) Titanium
b) Chromium
c) Titanium and Chromium
d) Neither titanium nor chromium
Answer: c
Explanation: Titanium and chromium metals are the metals that are spontaneously passivated on coupling with platinum. It is due to the mixed potential of galvanic couples lies in the protection region of the passive region.
14. Which of the following is/are correct regarding the potentiostat method?
a) It is a polarization technique that allows for controlled polarization
b) It works on controlling voltage between a working and reference electrode
c) It is a corrosion analysis method
d) It is a corrosion analysis technique method that allows for controlled polarization and it works on controlling voltage between a working and reference electrode.
Answer: d
Explanation: It is a corrosion analysis technique method that allows for controlled polarization and it works in controlling voltage between a working and reference electrode.
This set of Corrosion Engineering online quiz focuses on “Modern Theory Applications – Corrosion Rate Measurement”.
1. What is meant by anodic protection?
a) Accompanying the sacrificial metal with metallic structure
b) Prevention of corrosion by impressed cathodic current by supply electrons
c) Prevention of corrosion by the impressed anodic current is used to transform from active to a passive state
d) Additions of oxidizers and oxidizing agents for the formation of an oxide layer
Answer: c
Explanation: Anodic protection is one of the corrosion prevention or protection method in which the impressed anodic current is used to transform from active to a passive state.
2. The optimum potential for anodic protection is in the mid of passive region since it permits slight variations.
a) True
b) False
Answer: a
Explanation: Anodic protection is a corrosion prevention method in which anodic current of certain potential is provided to the metallic structure to transform from active to a passive state. The optimum potential for anodic protection is in the mid of passive region since it permits slight variations.
3. Which of the following is described in the given figure?
a) Protection range for anodic protection for an active metal
b) Protection range for anodic protection for an active-passive transition metal
c) Protection range for cathodic protection for an active-passive transition metal
d) Protection range for cathodic protection for an active metal
Answer: b
Explanation: The given figure depicts the anodic protection range for an active-passive transition metal. The optimum potential is usually at the mid-portion of a passive region of metal to permits slight variations.
4. Which of the following noble metals will improve the corrosion resistance of titanium and chromium on galvanic coupling?
a) Platinum
b) Palladium
c) Rhodium
d) Platinum, palladium, and rhodium
Answer: d
Explanation: Noble metals such as platinum, palladium, and rhodium on galvanic coupling will improve the corrosion resistance of titanium and chromium by spontaneous passivation. It is due to the mixed potential of the couple lies in the passive region of titanium and chromium.
5. Stainless steels containing small quantities of platinum passivates more readily in the presence of oxygen, ferric salts, and other oxidizing agents.
a) False
b) True
Answer: b
Explanation: Stainless steels containing small quantities of platinum passivates more readily in the presence of oxygen, ferric salts, and other oxidizing agents. It is due to the resultant mixed potential of an alloy that reaches a passive region quickly.
6. Which of the following electrochemical methods is/are used to determine the corrosion rate?
a) Tafel extrapolation
b) Linear polarization
c) Tafel extrapolation and linear polarization
d) Neither Tafel extrapolation nor linear polarization
Answer: c
Explanation: Tafel extrapolation and linear polarization are the two electrochemical methods used to determine the corrosion rate. These methods are extensively used for laboratory and industrial corrosion tests.
7. Which of the following is depicted in the given figure?
a) Electric circuit for cathodic polarization measurements
b) Electric circuit for anodic polarization measurements
c) Electric circuit for cathodic protection
d) Electric circuit for sacrificial anode system
Answer: a
Explanation: The given figure depicts the electric circuit for cathodic polarization measurements. This cathodic polarization is preferred over anodic polarization is due to the ease to measure experimentally.
8. The applied current cathodic polarization curve of a corroding metal is non-linear at low currents, but it becomes linear at higher currents on a semilogarithmic plot.
a) False
b) True
Answer: b
Explanation: The cathodic polarization curve is the curve drawn by measuring over voltage between reference and the working electrode on a semilogarithmic plot. It is non-linear at low currents whereas it becomes linear at higher currents.
9. Which of the following is depicted in the given figure?
a) Linear polarization curve
b) Mixed potential curve
c) Anodic polarization curve
d) Cathodic polarization curve
Answer: d
Explanation: The given depicts the cathodic polarization curve. Applied cathodic currents are equal to the difference between the current corresponding to the reduction process and that of the oxidation process. It is used to know the corrosion of metals.
10. Which of the following is/are the advantages of Tafel extrapolation?
a) It can measure extremely low corrosion rates
b) It can be used for continuously monitoring the corrosion rate of a system
c) It can be used for continuously monitoring the corrosion rate of a system with high accuracy and measures extremely low corrosion rates
d) It can be performed rapidly with high accuracy
Answer: c
Explanation: Advantages of Tafel extrapolation are:
It can measure extremely low corrosion rates
It can be used for continuously monitoring the corrosion rate of a system
It can be performed rapidly with high accuracy.
11. Which of the following is/are the limitations of Tafel extrapolation?
a) For reasonable accuracy, the Tafel region must be extended
b) It can be applied to systems containing one reduction process only
c) Much interference from concentration polarization
d) It can be applied to systems containing one reduction process, for reasonable accuracy the Tafel region must be extended and there will be much interference from concentration polarization
Answer: d
Explanation: Limitations of Tafel extrapolation are:
For reasonable accuracy, the Tafel region must be extended
It can be applied to systems containing one reduction process only
Much interference from concentration polarization.
12. What is the range of current density around corrosion potential that will observe that the applied current density is a linear function of the electrode potential?
a) 10 mV more noble or active around corrosion potential
b) 5 mV more noble or active around corrosion potential
c) 10 V more noble or active around corrosion potential
d) 5 V more noble or active around corrosion potential
Answer: a
Explanation: In around 10 millivolts around corrosion potential, it is observed that the applied current density is a linear function of the electrode potential. It is known as a linear polarization curve.
13. What is the formula to determine the slope of linear polarization curve?
a) ΔE/Δi =[2.3*icorr*]/[βa*βb]
b) ΔE/Δi=[βa+βb]/[2.3*icorr*]
c) ΔE/Δi=[βa*βb]/[2.3*icorr*]
d) ΔE/Δi=[2.3*icorr*]/[βa+βb]
Answer: c
Explanation: The slope of linear polarization curve is determined by using ΔE/Δi=[βa*βb]/[2.3*icorr*] where βa , βb are Tafel slopes of anodic and cathodic reactions and icorr is the current density at the intersection point of anodic and cathodic reaction.
14. Which of the following is depicted in the given figure?
a) Anodic polarization curve
b) Linear-polarization curve
c) Cathodic polarization curve
d) Mixed potential curve
Answer: b
Explanation: Linear polarization curve is drawn in around 10 millivolts around noble and 10 millivolts active around corrosion potential. It is used to determine the corrosion rate in industries and laboratory techniques by using formula ΔE/Δi = [βa*βb] / [2.3*icorr*].
15. Which of the following industries uses Tafel extrapolation or linear polarization to measure low corrosion rates?
a) Nuclear industries
b) Pharmaceutical industries
c) Food processing industries
d) Nuclear, pharmaceutical and food processing industries
Answer: d
Explanation: Nuclear, pharmaceutical, and food processing industries are the industries that use Tafel extrapolation or linear polarization where measuring low corrosion rates is important. Traces of impurities or contamination in these industries could lead to catastrophic failure.
This set of Corrosion Engineering Multiple Choice Questions & Answers focuses on “High-Temperature Corrosion – 1”.
1. Which of the following is/are the systems that are prone to high-temperature corrosion?
a) Gas turbines
b) Rocket engines
c) Furnaces
d) Gas turbines, rocket engines, and furnaces
Answer: d
Explanation: High-temperature systems such as gas turbines, rocket engines, and furnaces are prone to high-temperature corrosion due to high working temperature and petrochemical corrosive atmosphere around it.
2. Pilling and Bed worth proposed that oxidation resistance is related to the volume ratio of oxide and metal per grams atom of metal.
a) True
b) False
Answer: a
Explanation: Pilling and Bed worth proposed that oxidation resistance of a metal oxide is related to the volume ratio of oxide and metal per grams atom of metal.
3. Which of the following is/are the characteristics of a metal oxide if the Pilling and Bed worth ratio is less than 1?
a) Protective
b) Unprotective
c) Unprotective and insufficient oxide
d) Unprotective and sufficient oxide
Answer: c
Explanation: If Pilling and Bed worth ratio of a metal oxide is less than 1 then it is an unprotective and insufficient oxide, if it is near to 1 then it is protective and adherent and if it is greater than 1 then it is unprotective.
4. Which of the following is/are the causes for the poor oxidation resistance of metal oxide with high Pilling and Bed worth ratio?
a) Large compressive stresses in the oxide
b) Cracking
c) Spalling
d) Large compressive stresses in the oxide, cracking and spalling
Answer: d
Explanation: Metal oxides with a value greater than 1 Pilling and Bed worth ratio have poor oxidation resistance due to large compressive stresses in the oxide, cracking, and spalling.
5. Which of the following is/are the ideal characteristics of the passive metal oxide layer?
a) Good adherence and high melting point
b) Low electrical conductivity and low vapor pressure
c) Good adherence, high melting point, low vapor pressure, and low electrical conductivity
d) Good adherence and high vapor pressure
Answer: c
Explanation: Ideal characteristics of passive metal oxides layer are:
Good adherence
High melting point
Low electrical conductivity
Low vapor pressure
Low diffusion coefficient.
6. Which of the following metal has a nonprotective oxide?
a) Cadmium (CdO 2 )
b) Copper (Cu 2 O)
c) Chromium (Cr 2 O 3 )
d) Silicon (SiO 2 )
Answer: a
Explanation: Metal oxides can be categorized into protective and nonprotective based on the value of the Pilling and Bed worth ratio. Here, copper , chromium , and silicon are protective in nature whereas oxide of cadmium is unprotective.
7. What is the value of the Pilling and Bed worth ratio of tungsten?
a) 1.21
b) 3.40
c) 2.60
d) 0.45
Answer: b
Explanation: Pilling and Bed worth ratio is defined as the volume ratio of oxide and metal per grams atom of metal. The Pilling and Bed worth ratio of tungsten is around 3.40 and it is unprotective in nature.
8. Which of the following is/are the interface at which new metallic oxides are produced?
a) Metal-scale interface
b) Scale-gas interface
c) Metal-scale interface or scale-gas interface
d) Neither metal-scale interface nor scale-gas interface
Answer: c
Explanation: New metallic oxides is produced at a metal-gas interface or scale-gas interface based on the diffusion coefficient of metallic and oxygen ions in the metal matrix.
9. The diffusion of either cation or oxygen ions usually controls the reaction rate of high-temperature metallic oxidation.
a) True
b) False
Answer: a
Explanation: High-temperature metal-oxygen interaction can’t be separated electrically whereas diffusion of either cation or oxygen ions usually controls the reaction rate of high-temperature metallic oxidation.
10. Which of the following is depicted in the given figure?
a) Metal-liquid oxidation
b) Metal-gas oxidation
c) Metal-metal oxidation
d) Aqueous metal corrosion
Answer: b
Explanation: The given figure depicts the metal-gas oxidation and it also depicted the electrochemical process occurring during gaseous oxidation. It includes metal, metal oxide, and an oxygen atmosphere.
11. Which of the following order is correct regarding the oxides of iron starting from metallic iron to gaseous oxygen interface?
a) FeO, Fe 2 O 3 , and Fe 3 O 4
b) Fe 2 O 3 , Fe 3 O 4 and FeO
c) Fe 3 O 4 , Fe 2 O 3 , and FeO
d) FeO, Fe 3 O 4 , and Fe 2 O 3
Answer: d
Explanation: The most oxygen-rich compound is found at the scale-gas interface whereas a metal-rich compound is found at the metal-scale interface. Therefore, the correct order is FeO(22.270% O 2 ), Fe 3 O 4 (27.641% O 2 ), and Fe 3 O 4 (30.057% O 2 ).
12. The relative thickness of each phase of a metallic oxide is determined by the rate of ionic diffusion through that phase.
a) True
b) False
Answer: a
Explanation: The relative thickness of each phase of a metallic oxide is determined by the rate of ionic diffusion through that phase. Diffusion of ions may include metallic ions such as Fe +2 or Fe +3 or oxygen ions.
13. Which of the following metal produces metal oxide at a metal-scale interface?
a) Titanium
b) Niobium
c) Zirconium
d) Titanium, Niobium, and Zirconium
Answer: d
Explanation: Titanium, Niobium, Zirconium, Hafnium, and Tantalum are the metals that produce metal oxides at the metal-scale interface. It is due to the predominant diffusion of oxygen-ion rather than metallic cation.
14. Which of the following is/are the n-type semiconducting oxides?
a) CdO 2
b) TiO 2
c) Al 2 O 3 , CdO 2 , and TiO 2
d) CoO
Answer: c
Explanation: Semiconducting oxides such as CdO 2 , Al 2 O 3 , CdO, TiO 2 , Ta 2 O 5 , and SiO 2 are n-type semiconductors. It contains an excess of negatively charged electronic current carriers I.e. electrons.
Answer: b
Explanation: Semiconducting oxides such as FeO, MnO, Cu 2 O, and CoO are the p-type semiconducting oxides whereas Al 2 O 3 , CdO 2 are n-type oxides. In this, ionic transport occurs by metallic vacancies.
Sanfoundry Global Education & Learning Series – Corrosion Engineering.
This set of Corrosion Engineering online test focuses on “High-Temperature Corrosion – 2”.
1. In general, all oxides are nonstoichiometric in nature their composition varies from an ideal molecular formula.
a) True
b) False
Answer: a
Explanation: In general, all oxides are nonstoichiometric in nature their compositions vary from an ideal molecular formula. It is due to the excess or deficiency in metallic ions or equivalent oxygen ions.
2. Which of the following is/are correct regarding the measurement of the rate of oxidation?
a) Weight loss per unit area of metal is the measure of the rate of oxidation
b) Either weight loss or weight gain per unit area of metal is the measure of the rate of oxidation
c) Weight gain per unit area of metal is the measure of the rate of oxidation
d) Neither weight loss nor weight gain per unit area of metals is the measure of the rate of oxidation
Answer: c
Explanation: Rate of oxidation is usually measured and expressed in terms of weight gain per unit area of metal. As oxidation results in the conversion from metal M to metallic oxides MOn .
3. Diffusion-controlled oxidation can be minimized by decreasing the concentration of ionic defects in the scale.
a) False
b) True
Answer: b
Explanation: diffusion-controlled oxidation can be minimized by decreasing the concentration of ionic defects in the scale. These defects include Frenkel defect, Schottky defect, and many crystallographic defects.
4. What are the types of oxidation rate laws?
a) Linear and parabolic law
b) Cubic and logarithmic law
c) Linear, parabolic and cubic law
d) Linear, parabolic, cubic and logarithmic law
Answer: d
Explanation: Oxidation rate laws are classified based on the variation of oxidation rate in different metals. They are linear, parabolic, cubic, and logarithmic laws.
5. Which of the following oxidation rate law is depicted as x in the given figure?
a) Linear law
b) Parabolic law
c) Cubic law
d) Parabolic law
Answer: a
Explanation: The given figure depicts the graphical representation of oxidation laws. Linear oxidation law is denoted by letter x. Linear law states that weight gain per unit metal is directly proportional to the time of exposure.
6. Which of the following oxidation rate law is depicted as z in the given figure?
a) Linear law
b) Parabolic law
c) Cubic law
d) Parabolic law
Answer: c
Explanation: The given figure depicts the graphical representation of oxidation laws. Cubic law is denoted as letter z and it states that cube of weight gain per unit metal is directly proportional to the time of exposure.
7. Which of the following is/are correct regarding linear oxidation law?
a) Weight gain per unit area of the metal is directly proportional to the exposure time
b) It is a characteristic of porous or cracked scale
c) Sodium is an example that follows linear oxidation law
d) Weight gain per unit area of metal is directly proportional to exposure time, it is characteristic of porous or cracked scale and sodium follows linear oxidation law
Answer: d
Explanation: Linear oxidation law:
Weight gain per unit area of the metal is directly proportional to the exposure time
It is characteristics of porous or cracked scale
Sodium follows linear oxidation law.
8. Which of the following metal doesn’t follow linear oxidation law?
a) Sodium
b) Aluminum
c) Niobium
d) Potassium
Answer: b
Explanation: Linear oxidation law states that an increase in weight per unit area of metal is directly proportional to the time of exposure. Metals such as sodium, potassium, tantalum, and niobium follow linear oxidation law whereas aluminum follows the logarithmic oxidation law.
9. Which of the following is/are true regarding parabolic oxidation rate law?
a) It was proposed by C. Wagner
b) It states that square of weight loss is directly proportional to the time of exposure
c) It was proposed by C. Wagner which states that square of weight loss is directly proportional to the time of exposure and it resembles non-steady-state diffusion-controlled reactions
d) It resembles non-steady-state diffusion-controlled reactions
Answer: c
Explanation: True statements regarding parabolic oxidation rate law:
It was proposed by C. Wagner
It states that square of weight loss is directly proportional to the time of exposure
It resembles non-steady-state diffusion-controlled reactions.
Answer: d
Explanation: Logarithmic law is observed in thin sections of oxide layers at low temperatures. Metals such as aluminum, copper, iron, and other metals follow logarithmic oxidation rate law.
Sanfoundry Global Education & Learning Series – Corrosion Engineering.
This set of Corrosion Engineering Multiple Choice Questions & Answers focuses on “High Temperature Materials”.
1. Metals that follow linear oxidation kinetics at low temperatures tend to oxidize catastrophicallyat high temperatures.
a) True
b) False
Answer: a
Explanation: Metals that follows linear oxidation kinetics at low temperature tend to oxidize catastrophically at high temperatures. It is due to the rapid exothermic reactions at the surfaces at high temperatures.
2. Which of the following metals results in the ignition in extreme cases?
a) Sodium
b) Magnesium
c) Niobium
d) Sodium, magnesium, and niobium
Answer: d
Explanation: If the rate of heat transfer from metal to surroundings is less than heat evolution from oxide formation then it increases the surface temperature of metals. This leads to the ignition of metals and it includes sodium, magnesium, and niobium.
3. Which of the following metals results in the formation of volatile oxides?
a) Molybdenum
b) Tungsten
c) Osmium, tungsten, molybdenum, and Vanadium
d) Vanadium
Answer: c
Explanation: Volatile oxides are the oxides that get evaporate within the fractions of seconds after their formation. Metals that form volatile oxides include osmium, tungsten, molybdenum, and vanadium.
4. Which of the following is/are true regarding internal corrosion?
a) Corrosion products precipitate in the metal matrix
b) Corrosion products precipitate in the metal matrix and metals such as Fe, Ni, and Co are highly prone to internal corrosion
c) Corrosion occurs on external surfaces of metals
d) It is due to the stable corrosion products of base metals
Answer: b
Explanation: Internal corrosion is due to the one or more dilute alloying elements form more stable oxides than the base metal and preferentially forms corrosion in the metal matrix. Iron, nickel, and cobalt are the base metals that are prone to internal corrosion.
5. Dilute alloying elements of base metals exhibiting a relatively high solubility and diffusivity for atomic oxygen are subject to internal corrosion.
a) True
b) False
Answer: a
Explanation: Dilute alloying elements of base metals exhibiting a relatively high solubility and diffusivity for atomic oxygen are subject to internal corrosion. It is due to the formation of preferential stable oxides than the base metals.
6. Which of the following mechanical properties is/are important in structural applications of metals?
a) Tensile strength
b) Yield strength
c) Ductility and Elasticity
d) Tensile strength, Yield strength, Ductility, and Fracture toughness
Answer: d
Explanation: Mechanical properties that are important in structural applications of metals are:
i. Tensile strength
ii. Yield strength
iii. Ductility
iv. Fracture toughness.
7. Which of the following is/are correct regarding creep?
a) It is the continuous plastic elongation of metal under constant load
b) It is the high-temperature mechanical effect of a metal
c) It is the continuous plastic elongation of metal under constant load at high temperature and it can be minimized by the fraction of grain boundaries
d) It can be minimized by reducing the fraction of grain boundaries
Answer: c
Explanation: It is defined as the continuous plastic elongation of metal under constant load at high temperatures. Creep rate is then expressed as percent elongation in a given time. It can be minimized by reducing the fraction of grain boundaries.
8. Which of the following is/are true regarding stress rupture?
a) The stress required to cause a rupture in a predetermined time at a constant temperature
b) It is important in short-term high-temperature applications
c) Stress rupture is an important mechanical property for gas turbine or rocket engines
d) The stress required to cause a rupture in short-term high-temperature applications at a predetermined time is known as stress rupture and it is an important mechanical property for gas turbines and rocket engines
Answer: d
Explanation: Stress rupture is defined as the amount of stress that is required to cause a rupture in short-term high-temperature applications at a predetermined time. It is an important mechanical property for gas turbines and rocket engines.
9. Which of the following is/are the adequate high-temperature mechanical properties to avoid fracture?
a) Low creep rate and high stress-rupture strength
b) High stress-rupture strength, low creep rate, and high fracture toughness
c) High stress-rupture strength and high fracture toughness
d) Low creep rate and high fracture toughness
Answer: b
Explanation: Low creep rate, high stress-rupture strength, and high fracture toughness are the adequate high-temperature mechanical properties to avoid fracture.
10. Which of the following strengthening mechanisms is/are used to attain high-temperature strength?
a) Solid-solution strengthening
b) Precipitation hardening
c) Dispersion hardening
d) Solid-solution strengthening, precipitation hardening or dispersion hardening
Answer: d
Explanation: Strengthening mechanism that is used to attain high-temperature strength are:
i. Solid-solution strengthening
ii. Precipitation hardening
iii. Dispersion hardening.
11. Which of the following metallurgical changes that affect the structural stability of metals at high temperatures?
a) Grain growth, phase changes, precipitation dissolution and precipitation over aging
b) Grain growth and phase changes
c) Precipitation dissolution and precipitation over aging
d) Phase changes, precipitation dissolution and precipitation over aging
Answer: a
Explanation: Metallurgical changes that affect the structural stability of metals at high temperature are:
i. Grain growth
ii. Phase changes
iii. Precipitation dissolution
iv. Precipitation over aging.
12. Which of the following nickel-based alloys is/are superalloys?
a) Hastelloy C-276
b) Inconel 718
c) Hastelloy C-276, Inconel 718 and Hastelloy HX
d) Hastelloy HX
Answer: c
Explanation: Superalloys or high-performance alloys are the alloys that can resist extreme conditions such as high temperature, high stress, high wear, and corrosive atmospheres. Nickel-based alloys are widely used as superalloys that include Hastelloy C-276, Inconel 718, and Hastelloy HX.
13. Which of the following is/are the high melting point metals?
a) Molybdenum
b) Tungsten
c) Columbium
d) Molybdenum, tungsten, columbium, and tantalum
Answer: d
Explanation: Metals – Melting points
i. Tungsten – 6170°F
ii. Tantalum – 5430°F
iii. Molybdenum – 4750°F
iv. Columbium – 4380°F.
14. Which of the following is/are the limitations of high-temperature non-metallic materials?
a) Lack of ductility
b) Less resistance to thermal shock
c) Weldability, less resistance to thermal shock, lack of ductility and formability
d) Weldability and formability
Answer: c
Explanation: Limitations of high-temperature non-metallic materials are:
i. Lack of ductility
ii. Less resistance to thermal shock
iii. Lack of ductility
iv. Formability
v. Weldability.
This set of Corrosion Engineering Multiple Choice Questions & Answers focuses on “Corrosion and its Classification – 1”.
1. What is Corrosion?
a) Destruction or deterioration of a material
b) Conversion of metal atoms to metallic ions
c) Conversion of metal ions to metal atoms
d) Destruction of materials involving in the conversion of metal atoms into metal ions
Answer: d
Explanation: Corrosion is a destructive or deterioration of a material because of reaction with its environment. It occurs due to the higher stability of metal ions than the metal atoms.
2. Corrosion of metals is considered as the reverse of extractive metallurgy.
a) True
b) False
Answer: a
Explanation: Extractive metallurgy is a process of conversion of metal ions from the compounded state to metal atoms in the elemental state, whereas the corrosion occurs by the conversion of metal atoms into metal ions.
3. The chemical formula of rust is ______
a) Fe 1 O
b) Fe 2 O 3
c) Fe 3 O 4
d) Fe 2
Answer: b
Explanation: Corrosion of Iron is generally known as rusting. The chemical reaction can be represented as 4Fe + 3O 2 ==> 2Fe 2 O 3 .
4. Which of the following materials will undergo Corrosion?
a) Metals only
b) Metals and Non-metals
c) Metals, Non-metals, Ceramics and Plastics
d) Metals, Non-metals, Ceramics, Plastics and Rubbers
Answer: d
Explanation: Corrosion is defined as the destruction or deterioration of a material because of reaction with its environment. Every material in the universe will undergo corrosion but it varies in time and form. Any Physical, Chemical or Mechanical deviation of the original material is known as Corrosion.
5. Corrosion of material by furnace gases is classified as _____
a) wet corrosion
b) dry corrosion
c) galvanic corrosion
d) crevice corrosion
Answer: b
Explanation: Dry corrosion occurs in the absence of moisture usually by vapors and gases whereas the wet corrosion, galvanic corrosion and crevice corrosion occurs in aqueous state or in the presence of moisture.
6. Which of the following is an example of wet corrosion?
a) Corrosion of metal in the water
b) Corrosion of iron in the presence of anhydrous calcium chloride
c) Corrosion of titanium in dry chlorine
d) Corrosion due to furnace gases
Answer: a
Explanation: Wet corrosion occurs when the liquid is present. This usually involves aqueous solutions or electrolytes as corrosive mediums. Corrosion of iron in the presence anhydrous calcium chloride, by furnace gases and by dry chlorine are classified under dry corrosion.
7. Corrosion maintenance is vital in _____ industries.
a) paper
b) petroleum
c) plastic toy
d) both petroleum and paper
Answer: d
Explanation: The operating conditions in both the petroleum and paper industry are mainly in aqueous state with various chemicals in it. Hence these are likely prone to various electrochemical reactions which causes corrosion. Maintenance works include periodic inspection and replacements of partially corroded parts. It minimizes costly catastrophic failures, unscheduled down time, resulting in increased production and revenue.
8. Which of the following subjects are important in understanding and controlling corrosion?
a) Thermodynamics
b) Electrochemistry
c) Both Thermodynamics and Electrochemistry
d) Material Characterization
Answer: c
Explanation: Thermodynamic studies and calculations indicate the spontaneous direction of the reaction. The thermodynamic stability of corrosion product is relatively higher than reactant. Whereas the electrochemistry deals with electrode kinetics of the reaction.
9. Deterioration of paint and rubber by sunlight or chemicals is not a corrosion.
a) True
b) False
Answer: b
Explanation: Any deviation in the physical, chemical and mechanical properties of a material is considered as corrosion. Here we can notice physical change so it is a corrosion.
10. Which of the following is an incorrect statement?
a) Corrosion is an irreversible process
b) Corrosion is a non-spontaneous process
c) Corrosion is a degradation process
d) Corrosion is a spontaneous process
Answer: b
Explanation: Corrosion is a spontaneous process which results in degradation of materials and it is irreversible in nature. Spontaneous reaction is a reaction which results in the formation of stable products from unstable without need of any external energy.
11. Which of the following is considered as high corrosive resistant material?
a) Mild steel
b) Cast iron
c) Zinc
d) Stainless steel
Answer: d
Explanation: Corrosion resistant material is the material which has less corrosion rate in a particular atmosphere without much degradation. Stainless steel is considered as corrosion resistant material. This is because it forms chromic oxide layer over its surface to avoid physical contact with the outside environment.
12. Corrosion involves _______ reactions.
a) oxidation
b) reduction
c) displacement
d) both oxidation and reduction
Answer: d
Explanation: Corrosion is an electrochemical reaction. It occurs by therelease and gain of electrons from various species which are termed as oxidation and reduction respectively. It can be observed with change in the oxidation state of the species.
13. Which of the following are necessary in the process of corrosion?
a) Anode
b) Cathode
c) Electrolyte
d) Anode, Cathode and Electrolyte
Answer: d
Explanation: Corrosion occurs by the creation of electrochemical cell which includes a cathode, an anode and an electrolyte. A high reduction potential will act as cathode and other will acts as anode preferentially and electrolyte is needed to transfer ions between these two electrodes.
14. What is the reason for corrosion?
a) Stability of a metal ion
b) Stability of a metal atom
c) Passivation
d) Use of coatings
Answer: a
Explanation: Negative or less Gibbs free energy of the metal ions is the reason for corrosion whereas passivation and use of coatings decreases the extent of corrosion.
15. What are the advantages of corrosion?
a) Protection of metals by surficial oxide layer
b) Zn-carbon electrochemical reactions in the battery
c) Decrease in the strength of material
d) Protection of metals by the surficial oxide layer and Zn-carbon electrochemical reactions in the battery
Answer: d
Explanation: Initially passivating metals undergoes corrosion in order to form oxide layer. These thick, dense oxide layer acts as a strong barrier and protects the inner metal against corrosion. The Zn-carbon batteries works on the principle of galvanic corrosion. It involves conversion of chemical energy into electrical energy by these electrochemical reactions.
This set of Corrosion Engineering Interview Questions and Answers focuses on “Corrosion and its Classification – 2”.
1. Which of the following factors affect the corrosion rate of metal?
a) Relative surface area of an anode and cathode
b) Nature of the oxide layer
c) Purity of metal
d) Relative surface area of an anode and cathode, nature of oxide layer and purity of metal
Answer: d
Explanation: As the cathodic to anodic area increases, the more oxygen reduction, or more corrosion can occur. The corrosion resistance of aluminum can be attributed to the formation of the thick, dense oxide layer. Impure metals undergo corrosion at a faster rate than the pure metals.
2. The cathodic reaction that occurs during corrosion in oxygenated acidic solution is ______
a) 2H + +2e – ==>H 2
b) 4H + +O 2 +4e – ==>2H 2 O
c) 2H 2 O+2e – ==>H 2 +2OH –
d) 2H 2 O+O 2 +4e – ==>4OH –
Answer: b
Explanation: The common hydrogen reduction reaction in corrosion will proceed based on the pH and the amount of oxygen present in the solution. Then oxygenated acidic solution will react as
4H + +O 2 +4e – ==>2H 2 O.
3. If a metal undergoes uniform corrosion it becomes _____
a) thinner
b) thicker
c) perforated
d) thicker and perforated
Answer: a
Explanation: Uniform corrosion is the most common form of corrosion. It is characterized by an electrochemical reaction that proceeds uniformly over the entire exposed surface. Thus, the metal becomes thinner.
4. Which theory explains the oxidation of metals?
a) Collison theory
b) Molecular orbital theory
c) Wagner’s theory
d) Mixed potential theory
Answer: c
Explanation: Wagner’s theory states that the oxidation of metal is electrolytic in nature and the rate of oxidation is determined by the electrical properties of the corrosion product.
5. What is the mechanism of dry corrosion?
a) Absorption
b) Electrochemical
c) Differential solubility
d) Both electrochemical and differential solubility
Answer: a
Explanation: Dry corrosion occurs in the absence of a liquid phase. Vapors and gases are usually the corrodents. These will hit and adsorbed on the metal surface to form corrosion. So dry corrosion can be explained by an absorption mechanism.
6. Which of the following corrosion contaminant will act as a protective layer?
a) AgCl
b) SnCl 2
c) Fe 2 O 3
d) CaO
Answer: a
Explanation: Silver on reaction with chlorine forms silver chloride. It acts as a protective layer and prevents chlorine to corrode further. Here SnCl 2 and CaO are volatile in nature whereas Fe 2 O 3 is porous in nature. Hence, they can’t act as protective layers.
7. Corrosion of iron takes place even in the solid ice.
a) True
b) False
Answer: b
Explanation: Though ice is the solid form of water but it doesn’t conduct electrons. The function of an electrolyte is to transfers ions from one electrode to another. Thus, given statement is false. Corrosion needs an anode, a cathode and a conductive electrolyte.
8. What are the factors that affect corrosion?
a) Temperature
b) Humidity
c) Conductance of the corroding medium
d) Temperature, humidity and conductance of the corroding medium
Answer: d
Explanation: The main factors that affect the rate of corrosion includes the effect of pH, temperature, humidity, conductance of the corroding medium, oxygen concentration, presence of impurities. These factors are based on the nature of environment.
9. _______ is a chemical substance which reduces the corrosion rate.
a) Corrosion inhibitor
b) Corrosion initiator
c) Electrolyte
d) Corrosive medium
Answer: a
Explanation: An inhibitor is a substance that, when added in small concentrations to an environment, decreases the corrosion rate.
Following are the types of inhibitors:
i. Adsorption-type
ii. Hydrogen-evolution poisons
iii. Scavengers
iv. Vapor-phase
10. In the given figure, what does point A denote?
a) Cathodic spot
b) Anodic spot
c) Electrolyte
d) Oxide layer
Answer: a
Explanation: Cathodic spot, a place on the metal surface where the reduction reaction takes place. Reduction is a process in which atoms of the chemical reaction accepts electrons in order to form anion.
11. In the given figure, what does point B denote?
a) Cathodic spot
b) Anodic spot
c) Electrolyte
d) Oxide layer
Answer: b
Explanation: Anodic spot, a place on the metal surface where the oxidation reaction takes places. Oxidation is a loss of electrons or increase in the oxidation state during a reaction by a molecule or atom. Molecules or atoms on oxidation forms cations. Ex: Fe ==> Fe +2 + 2e – .
12. In the given figure, what does point C denote?
a) Cathodic spot
b) Anodic spot
c) Electrolyte
d) Oxide layer
Answer: c
Explanation: Electrolyte is a conductive medium between anode and cathode. It undergoes ionization when dissolved in water or ionizing solvents. The function of an electrolyte is to transfers ions from one electrode to another.
This set of Corrosion Engineering Multiple Choice Questions & Answers focuses on “Corrosion Damage”.
1. Which of the following are the destructive effects of corrosion?
a) Contamination of product
b) Effect on safety
c) Reliability
d) Contamination of product, effect on safety and reliability
Answer: d
Explanation: The market value of the product depends on purity and quality. Contamination of product decreases the market value of the product. Safety and reliability are the major concerns due to the catastrophic nature of corrosion. Economizing on materials of construction is not desirable if safety is risked.
2. Preventive action on corrosion is necessary and economical.
a) True
b) False
Answer: a
Explanation: Preventive action involves the replacement of partially corroded or failed equipment. It avoids plant shutdowns and contamination of a product. Hence, the process become more economical.
3. Which of the following corrosion damage is more emphasized in the construction material of restaurants?
a) Loss of appearance
b) Maintenance and operating cost
c) Effect of safety
d) Both loss of appearance and effect of safety
Answer: d
Explanation: Restaurants and in many other public places, the main concern about the corrosion is that the loss of appearance and effect of safety. Badly corroded and rusted products would leave a poor impression on the observer.
4. Etchants react with metallic surface and get corroded in order to use for the metallurgical investigation.
a) True
b) False
Answer: a
Explanation: We can’t differentiate grain and grain boundaries in a non-etched polished sample. Etchant is used to react with the grain boundaries in order to reveal grain and grain boundaries.
5. Main form of ceramic degradation is _________
a) dissolution
b) swelling
c) weathering
d) dissolution and swelling
Answer: c
Explanation: Weathering is the main form of degradation of ceramics. Weathering involves breakdown of ceramics through contact with the earth’s atmosphere, water, and biological organisms.
6. Which of the following are included in maintenance and operating costs?
a) Use of corrosion-resistant material
b) Loss of product
c) Regular inspections
d) Use of corrosion-resistant material and regular inspection
Answer: d
Explanation: Maintenance and operating costs are the preventive measures in order to avoid the plant shutdowns and catastrophic accidents. Plant shutdowns usually cost 5-10 times more than the maintenance and operating costs.
7. The effect of acid rains on Taj Mahal is also a corrosion.
a) True
b) False
Answer: a
Explanation: Oxides of carbon, Sulphur and nitrogen on reacting with rain water, forms dilute acids. These acids on reaction with the marble of Taj mahal degrades its appearance, hence it is regarded as corrosion. Acid rains also accelerates the natural corrosion and erosion.
8. Portable water pipelines of lead are replaced by various types of steels, due to _____
a) cheaper cost
b) more availability
c) contamination caused by lead
d) shiny appearance
Answer: c
Explanation: Lead exposure is a public health hazard as it causes development effects in infants and young children. Lead contamination in drinking water is the most contributor of lead exposure to humans. To avoid exposure, various steels such chromium steels and coated steels are being used for this purpose.
9. Which of the following tragediesthat occurred due to corrosion?
a) Bhopal tragedy
b) Crude oil leak in Canada
c) Both Bhopal tragedy and crude oil leak in Canada
d) Fukushima
Answer: c
Explanation: Bhopal gas tragedy is caused by the immediate flow of water into Methyl isocyanate gas tank. This resulted in the formation of much carbon dioxide and the temperature inside the tank reach over 200°C. Crude oil leakage in Canada occurred in 2017, occurred due to corrosion at the sealing.
10. Thermal gradients across the metal wall causes Stress cracking corrosion.
a) True
b) False
Answer: a
Explanation: Thermal gradients across the metal wall induces higher stresses in the metal. Internal stresses in the corrosive environments is the reason for the stress corrosion cracking.
This set of Advanced Corrosion Engineering Questions and Answers focuses on “Corrosion Rate Expression”.
1. What is meant by MPY in corrosion?
a) Mils penetration per year
b) Meter penetration per year
c) Milli meter penetration per year
d) Micro meter penetration per year
Answer: a
Explanation: MPY in corrosion is abbreviated as Mils penetration per year . It is usually used in the U.S. measurement system in order to estimate the corrosion rate of pitting corrosion.
2. Which of the following expression is used to calculate MPY?
a) MPY=/DAT
b) MPY=/DAT
c) MPY=W/DAT
d) MPY=DAT/
Answer: b
Explanation: W = weight loss in milligrams, D=Density of a specimen (g/cm 3 ), A=Area of specimen, T=time of exposure in hours and 534 is a conversion factor. MPY means mils penetration per year I.e. milli inches penetration per year.
3. MDD in corrosion is abbreviated as ______
a) milligrams/sq. decimeter/decade
b) millimeters/sq. decimeter/day
c) milligrams/sq. decimeter/day
d) microns/decimeter/decade
Answer: c
Explanation: MDD in corrosion known as milligrams/sq.decimeter/day. It is the common unit to measure weight loss of metal per unit area. It is usually used for uniform and galvanic corrosion.
4. MPY is used to measure weight loss per unit area.
a) True
b) False
Answer: b
Explanation: Usually mils per year is used to measure the penetration rate. Penetration is the average depth of metal loss in the specimen. MPY is usually used for pitting corrosion. MDD is used to measure the weight loss per unit area.
5. _____ is/are used to measure the extent of pitting corrosion.
a) MPY
b) MDD
c) Both MPY and MDD
d) MPK
Answer: a
Explanation: Pitting corrosion involves loss of metal at the selected spots on the surface of a metal. It penetrates into various depths based on the concentration of corrosive medium and nature of metal. MPY measures penetration range.
6. Which of the following law is used to derive the corrosion rate expression?
a) Newton’s law
b) Henry’s law
c) Raoult’s law
d) Faraday’s law
Answer: d
Explanation: Faraday’s law is used in order to derive the corrosion rate expression [W/At=I*a m /n*F]. W/At denotes the corrosion rate, I=current density, a m =molecular weight, n=number of electrons transferred, F=faraday constant .
7. Which following expression is used to find the corrosion rate from current density of a corroding specimen?
a) W/At = [(I × a m ) / ]
b) W/At = [(I × a m ) / ]
c) W/At = [534 × (I × a m ) / ]
d) W/At = [(I × a m ) / ] and W/At = [(I × a m ) / ]
Answer: d
Explanation: W/At denotes the corrosion rate, I= current density, am=molecular weight, n=number of electrons transferred, F=faraday constant , d=density of a specimen. [(I*a m ) / ] is used to calculate the MDD whereas the [(I*a m ) / ] is used to calculate the MPY.
8. Rate of oxidation is equals to the rate of reduction in corrosion.
a) True
b) False
Answer: a
Explanation: It is the second statement in the mixed potential theory that the number of electrons generated and consumed are same. Anode produces the same number of electrons that require for the cathode.
9. Iron is corroding at a current density of 1.69*10 -4 amp/cm 2 . What would be the corrosion rate in MDD?
a) 773
b) 723
c) 423
d) 473
Answer: c
Explanation: We know MDD = W/At = (I*a m ) / . We should convert the given unit values in milligrams/sq. Decimeter/day.
Given, I = 1.69*10 -4 amp/cm 2
Atomic weight of iron = a m = 55.86 g/mol
n = number of electrons = 2 [Fe ==> Fe +2 +2e – ]
F = faraday’s constant = 96500 coulombs
= (1.96×10 -4 coulombs /sec*cm 2 ) × ÷ (2×96500 coulombs )
= [(1.96×10 -4 )***(55.86 *10 3 )] / [2*96500]
= 422.53 MDD.
10. Iron is corroding at a current density of 1.69*10 -4 amp/cm 2 . What would be the corrosion rate in MPY?
a) 423
b) 77
c) 473
d) 97
Answer: b
Explanation: We know MDD = W/At = (I*a m ) / . We should convert the given unit values in milli inches per year.
Given, I = 1.69*10 -4 amp/cm 2
Atomic weight of iron = a m = 55.86 g/mol
n = number of electrons = 2 [Fe ==> Fe +2 +2e – ]
F = faraday’s constant = 96500 coulombs
d=density of iron = 7.875 g/cm 3
= [(1.96×10 -4 coulombs/sec*cm 2 ) × ] ÷ [(7.874 g/cm 3 ×2×96500 coulombs)]
= [(1.96×10 -4 coulombs /sec* cm 2 ) × ] ÷ [(7.874 g/ cm 2 *cm×2×96500 coulombs )]
= [(1.96×10 -4 1/sec) × ] ÷ []
= [1.69×10 -4 × × × 10 3 ] / [2 × 96500 × 7.875 × 2.54]
= 77.117 MPY.
11. _____ is used to measure the extent of uniform corrosion.
a) MDD
b) MPY
c) Both MPY and MDD
d) MPE
Answer: a
Explanation: Uniform corrosion is the corrosion that occurs throughout the entire exposed surface of a metal and it is uniform in depth of corrosion layer. Weight loss method I.e. MDD is used to know the extent of uniform corrosion.
12. Corrosion rate of aluminum is _________ when compared with corrosion of mild steel in open oxygenated atmosphere.
a) small
b) medium
c) large
d) very small
Answer: d
Explanation: In oxygenated atmosphere aluminum has high corrosion resistant than the mild steel due to its oxide layer formation. Hence the corrosion rate of aluminum is very small when compared to the corrosion rate of mild steel.
13. ___________ will occur, if current pass from an electrode to electrolyte.
a) Oxidation
b) Reduction
c) Oxidation and reduction
d) Anion formation
Answer: a
Explanation: The direction of current flow is exactly opposite to the movement of electrons. We know electrons starts at the anode and travels towards cathode whereas current will flow from anode to electrolyte. This results in oxidation or corrosion on that electrode.
14. Oxidizing impurities in electrolyte increases the corrosion rate.
a) True
b) False
Answer: a
Explanation: Mixed potential theory states that any electrochemical reaction can be divided into two or more partial reactions . Presence of oxidizing impurities such as Fe +3 increases the number of reduction reactions. It correspondingly increases the oxidation rate or corrosion rate.
15. What are the uses of corrosion rate estimation of materials in daily life?
a) To predict the life time of a component
b) To compare the corrosive-resistant of materials
c) To increases the corrosion rate
d) To predict the life time and to compare the corrosive resistant of materials
Answer: d
Explanation: Corrosion rate expression is used to quantify the corrosion process. This helps us to predict the life time of a component and to compare with different materials. This also helps us to change the process variables in order to decrease the corrosion rate.
This set of Corrosion Engineering Multiple Choice Questions & Answers focuses on “Corrosion Principles – Electrochemical Aspects – 1”.
1. Which of the following products are obtained when a zinc metal is dipped in dilute HCl solution?
a) H 2 , ZnCl 2
b) Cl 2 , ZnH 2
c) H 2 , Cl 2 and ZnH 2
d) Zn, H 2 and Cl 2
Answer: a
Explanation: When zinc is placed in dilute hydrochloric acid, a vigorous reaction occurs. Hydrogen gas is evolved and the zinc dissolves, by forming a solution of zinc chloride.
Anodic reaction: Zn==>Zn +2 +2e(Zn +2 +2Cl – ==>ZnCl 2 )
Cathodic reaction: 2H + +2e==>H 2
2. Which of the following reactions occurs when iron is immersed in sea water?
a) Fe==>Fe +2 +2e, 2H + +2e==>H 2
b) Fe==>Fe +2 +2e, O 2 +2H 2 O+4e==>4OH –
c) Fe +2 +2e==>Fe +2 , 4H + +O 2 +4e==>2H 2 O
d) Fe +2 +2e==>Fe +2 , 2H + +2e==>H 2
Answer: b
Explanation: Iron dissolution Fe==>Fe +2 +2e. Oxygenated hydrogen reaction in a neutral solution is O 2 +2H 2 O+4e==>4OH – .
3. Which of the following is more stable form of iron in an oxygenated solution?
a) Fe 2 O 3
b) Fe 2
c) 2Fe 3
d) Fe 3 O 4
Answer: c
Explanation: +3 oxidation state of iron is more stable state of iron than +2 oxidation state. The reaction is follows as
Fe+H 2 O+½O 2 ==>Fe 2
2Fe 2 +H 2 O+1/2O 2 ==>2Fe 3 .
4. Which of the following are the types of chemical reactions?
a) Combination and Decomposition reactions
b) Combination and Single displacement
c) Single and Double displacement reaction
d) Combination, Decomposition, Single displacement and double displacement
Answer: d
Explanation: Combination reaction: A+B==>C,
Decomposition reaction: A==>B+C,
Single displacement reaction: AB+C==>AC+B
Double displacement reaction: AB+CD==>AC+BD
5. More than one anodic and cathodic reactions are possible in corrosion.
a) True
b) False
Answer: a
Explanation: Mixed potential theory states that any electrochemical reaction can be divided into two or more partial reactions . Dissolution of an alloy in pure acid involves more than one anodic reaction. Corrosion of pure metal in oxygenated impure acid involves more than one cathodic reaction.
6. Oxygenated acids are more corrosive than oxygen-free acids.
a) True
b) False
Answer: a
Explanation: Case1
Anodic reaction: M==M> +n +ne
Cathodic reaction: 2H + +2e==>H 2
Case2
Anodic reaction: M==>M +n +ne
Cathodic reaction: 2H + +2e==>H 2 , O 2 +4H + +4e==>2H 2 O
This oxygen reduction increases the cathodic rate which correspondingly increases the anodic rate or corrosion rate.
7. Which of the following parameter of electrolyte decreases the corrosion rate?
a) Dissolved oxygen
b) Temperature
c) High electrical resistance
d) Presence of ferric ions
Answer: c
Explanation: The Function of an electrolyte is to transfer the ions between anode and cathode. Increase in electrical resistance in electrolyte shows obstruction for the free flow of ions, hence the corrosion rate decreases. Whereas dissolved oxygen, temperature and presence of ferric ions increases the mobility of ions and increases the corrosion rate.
8. Which of the following are the types of polarization?
a) Activation polarization
b) Activation and Concentration polarization
c) Resistance polarization
d) Activation, Concentration and Resistance polarization
Answer: d
Explanation: Polarization is the potential difference occurred due to the non-equilibrium conditions, due to the change in concentration or temperature. These are classified into three types. They are i) Activation polarization ii) Concentration polarization iii)Resistance polarization.
9. Which of the following is depicted in the given figure?
a) Activation polarization
b) Concentration polarization
c) Resistance polarization
d) Concentration and Resistance polarization
Answer: a
Explanation: Activation polarization refers to an electrochemical process that is controlled by the reaction sequence at the metal-electrolyte interface.
Step 1: Species adsorbed on the metal surface
Step 2: Electron transfer
Step 3: Reduction of species
Step 4: Combine to form a bubble of hydrogen molecule.
10. Which of the following is depicted in the given figure?
a) Activation polarization
b) Concentration polarization
c) Resistance polarization
d) Both Activation and Resistance polarization
Answer: b
Explanation: Concentration polarization refers to an electrochemical process that is controlled by the diffusion of ions from bulk solution to the metal-electrolyte interface. This usually occurs in low concentration electrolytes.
This set of Corrosion Engineering Questions and Answers for Freshers focuses on “Corrosion Principles – Electrochemical Aspects – 2”.
1. Concentration polarization is considered in both anodic and cathodic reactions.
a) True
b) False
Answer: b
Explanation: Concentration polarization refers to the electrochemical reaction that is controlled by the diffusion of ions in an electrolyte. This occurs in the low concentration of electrolyte. It is neglected in the case of anodic reaction because there is a sufficient supply of metal atoms in a metallic piece and there is no need for diffusion.
2. Which of the following polarization will be influenced by electrolytic agitation?
a) Activation polarization
b) Resistance polarization
c) Concentration polarization
d) Both Activation and Resistance polarization
Answer: c
Explanation: Concentration polarization refers to the electrochemical reaction that is controlled by the diffusion of ions in an electrolyte. With an increase in the velocity or agitation of the electrolyte the contact of ions with metal interface increases.
3. What is meant by passivation?
a) Loss of reactivity
b) Increase in reactivity
c) Increase in corrosion rate
d) Deterioration of metal
Answer: a
Explanation: Passivation is the state of metal in which stable films or barriers are formed. These stable films obstruct the contact of corrosive medium to the metal surface. Most of the engineering metals undergo passivation under different atmospheric conditions.
4. Which of the following metal is depicted in the given graph?
a) Active metal
b) Passive metal
c) Active-Passive metal
d) Trans passive state of metal
Answer: a
Explanation: The corrosion rate of active metal increases with an increase in the oxidizing potential of the environment. In the case of passive metal, it remains almost constant at a lower corrosion rate value. Whereas in the case of trans passive state of metal the corrosion increases from a certain value due to the damage of protective film.
5. Which of the following metal is depicted is in the given figure?
a) Active metal
b) Passive metal
c) Active-Passive transition metal
d) Trans passive state of metal
Answer: c
Explanation: Active-Passive transition metal is a metal that undergoes a transition from active to passive state after a certain oxidation potential. The oxidation potential from which the passivation starts is called critical oxidation potential. Fortunately, most of the engineering metals are active-passive metals that protect from corrosion.
6. What is the trans passive region?
a) Region after passive state
b) Formed by breakage of the protective film in the passive region
c) Constant corrosion rate
d) Region formed after passive state by breakage of the passive oxide layer
Answer: d
Explanation: Trans passive region is formed in an active-passive transition metal after crossing the limiting oxidizing potential after a passive region. This occurs due to the breakage of the protective layer due to the unbearable oxidizing potential of the corrosive medium.
7. Which of the following is denoted as // in an electrochemical cell notation?
a) Anode
b) Cathode
c) Electrolyte
d) Salt bridge
Answer: d
Explanation: Salt bridge is a connection between two half cells used to neutralize the ions with respective opposite charged ions. Usually, strong electrolytes such as KCl along with agar-agar gel are used.
8. Which of the following gives Standard cell potential of a cell (E o )?
a) E o cathode -E o anode
b) E o anode -E o cathode
c) E o cathode *E o anode
d) E o anode /E o cathode
Answer: a
Explanation: A electrochemical cell consist of two electrodes with a potential difference preferentially one acts as a cathode and other as an anode. The standard state of each specific electrode is constant and it measured against the hydrogen electrode at 25°C and 1 atm pressure. And standard cell potential is calculated as E o cathode -E o anode .
9. Which of the following is a Nernst equation?
a) E cell =E o cell –RT/nF ln
b) E cell =E o cell –nF/RT ln
c) E 0 cell =E cell –RT/nF ln
d) E 0 cell =E cell –nF/RT ln
Answer: a
Explanation: E cell =E o cell –RT/nF ln is the Nernst equation. E o cell is the potential of a cell in the standard state, R is Universal gas constant, n is the valency of ion, T is absolute temperature, F is Faraday’s constant and K is the reaction quotient, E cell is the cell potential.
Answer: a
Explanation: Chemical reaction can be written as Zn + 2Ag +1 ==>Zn +2 +2Ag
E o cell =0.80- (since E o silver=0.80V, E o zinc=-0.763V)
E o cell =1.563V
E cell =E o cell –RT/nF ln
E cell =1.563-[/2*96500)]ln
E cell =1.563-[/2*96500)]ln
E cell =1.563-[/2*96500)]ln
E cell =1.563+0.01283
E cell =1.57583 V.
This set of Corrosion Engineering Multiple Choice Questions & Answers focuses on “Corrosion Principles – Effect of Oxygen and Velocity”.
1. What is the nature of region number 1 in the given figure?
a) Active region
b) Passive region
c) Trans passive region
d) Active-Passive transition region
Answer: a
Explanation: The active region is the region in which the corrosion rate increases with an increase in oxidizer concentration. Iron in oxygenated water is the best example of an active region. Because iron will not undergo the transition to passive region irrespective of the concentration of oxygen present at room temperature.
2. What is the nature of region number 2 described in the given figure?
a) Active region
b) Passive region
c) Trans passive region
d) Active-Passive transition region
Answer: b
Explanation: The passive region is the region in which the corrosion rate is very less and even become independent with the concentration of oxygen. Hastelloy C in FeCl 3 solution is the best example of a passive state region.
3. What is the nature of region number 3 in the given figure?
a) Active region
b) Passive region
c) Trans passive region
d) Active-Passive transition region
Answer: c
Explanation: Trans passive transition is obtained from passive state due to the presence of a high concentration of oxidizers. This transition initiated with the breakage of protective films and it increases exponentially with the increase in oxidizer concentration.
4. Passivity is achieved only if a sufficient quantity of oxidizer is added to the medium.
a) True
b) False
Answer: a
Explanation: In practical cases, the corrosion rate is estimated based on the current density generated. We know that the current density increases with the increase in oxidizer concentration and passivity will only be achieved when the current density crosses critical current density value (i c ).
5. Which of the following metal-acid combination will shift metal from active to passive state with an increase in oxidizer concentration?
a) Monel in HCl+O 2
b) 18Cr-8Ni in H 2 SO 4 +Fe +3
c) Fe in H 2 O+O 2
d) 18Cr-8Ni in HNO 3 + Cr 2 O 3
Answer: b
Explanation: Initially corrosion rate of Stainless steel in sulfuric acid increases with an increase in the concentration of ferric ion (Fe +3 ). And then it is followed by a rapid decrease in corrosion rate due to the formation of a passive layer. Critical current density (i c ) must be achieved to undergo the transition from active to passive.
6. What is the nature of copper corrosion in oxygenated sulfuric acid?
a) Active region
b) Passive region
c) Active-Passive transition region
d) Trans-passive region
Answer: a
Explanation: Copper will act as an active metal in sulfuric acid, the corrosion rate increases with an increase in oxygen concentration. And the passivity is not achieved irrespective of the oxidizer added.
7. The corrosion rate depends on both the medium and the metal involved.
a) True
b) False
Answer: a
Explanation: We know that different metals will respond differently in the same medium. In another case, the same metal shows different characters in different mediums. Thus, the corrosion rate depends on both the medium and the metal involved in the reaction.
8. What is the other name of concentration polarization?
a) Anodic diffusion control
b) Cathodic diffusion control
c) Erosion corrosion
d) Activation polarization
Answer: b
Explanation: Concentration polarization is also called as cathodic diffusion control. Concentration polarization is controlled by the diffusion of ions from the bulk solution to the metal electrolyte interface. This diffusion can be accelerated by agitation or by increasing the velocity of the solution.
9. Which of the following metals are more corrosion resistant in a high-velocity corrosive solution?
a) Stainless steel
b) Lead
c) Titanium
d) Both stainless steel and titanium
Answer: d
Explanation: Stainless steel and titanium are easily passivating material and easily get passivated in high-velocity mediums. These metals form a stable oxide layer that can resist high velocities of corrosive medium.
10. Which of the following corrosion is indicated by the C curve in the given figure?
a) Uniform corrosion
b) Galvanic corrosion
c) Erosion corrosion
d) Stress cracking corrosion
Answer: c
Explanation: Erosion corrosion is the mechanical damage of the material due to the high velocity of the medium. The effect of agitation or velocity will have a negligible effect until the mechanical damage initiates.
11. Which of the following reaction is depicted by curve A in the given figure?
a) Fe in dilute HCl
b) Pb in dilute H 2 SO 4
c) 18Cr–8Ni in H 2 SO 4
d) 18Cr–8Ni in H 2 SO 4 +Fe +3
Answer: d
Explanation: Stainless steel in H 2 SO 4 with the impurity of ferric ions (Fe +3 ) follows curve A. Initially, the corrosion rate of stainless-steel increases with the increase in velocity up to critical current density (i c ). Then the corrosion rate of stainless-steel decreases rapidly and becomes almost constant due to passivation.
This set of Corrosion Engineering Interview Questions and Answers for freshers focuses on “Effect of Temperature and Corrosive Concentration”.
1. The rate of chemical reaction increases with an increase in temperature.
a) True
b) False
Answer: a
Explanation: Temperature increases the rate of almost all the reactions because it increases the kinetic energies of atoms or ions. This increase in kinetic energy makes them react to each other to get stable products. It also increases the mobility of ions in the electrolyte.
2. What is the corrosion rate behavior of curve A with the increase in temperature, described in the given figure?
a) Constant
b) Exponential increase
c) Exponential decreases
d) Slightly decreases
Answer: b
Explanation: Curves A and B represent the corrosion behavior of different materials with an increase in temperature. Here curve A indicates the exponential increase in corrosion rate with the temperature. Example: Iron in hydrofluoric acid.
3. What is the corrosion rate behavior of curve B with the increase in temperature, described in the given figure?
a) Exponential increase
b) Exponential decrease
c) Constant up to high temperatures
d) Slightly decreases
Answer: c
Explanation: Here curve B indicates the uniform corrosion rate up to very high temperatures, this is due to the formation of protective oxide layers. At very high temperatures, it results in the transformation of trans passive region which increases the corrosion rate exponentially.
4. In which of the following reactions, we observe the exponential increase in corrosion rate with an increase in temperature?
a) 18Cr-8Ni in H 2 SO 4
b) 18Cr-8Ni in HNO 3
c) Ni in NaOH
d) Monel in HF
Answer: a
Explanation: Stainless steel in sulfuric acid will corrode exponentially with the increase in temperature. Whereas stainless steel in nitric acid, nickel in sodium hydroxide, monel for hydrofluoric acid are the best corrosion-resistant materials in respective mediums and suffer less corrosion with the increase in temperature.
5. In which of the following reactions, we observe the unaffected corrosion rate with the increase in temperature?
a) 18Cr–8Ni in HNO 3
b) 18Cr-8Ni in H 2 SO 4
c) Ni in HCl
d) Fe in HF
Answer: a
Explanation: Stainless steel in the HNO 3 medium will have a negligible effect on the corrosion rate with the increase in temperature. It forms a stable oxide layer and avoids the exposure of a corrosive atmosphere to the metallic surface. It is stable up to very high temperatures.
6. What is the corrosion rate behavior of curve B with the increase in corrosive concentration, described in the given figure?
a) Exponential increases
b) Exponential decreases
c) Constant
d) First increases and then decreases
Answer: d
Explanation: The given figure represents the corrosion behavior of different materials with an increase in the concentration of the corrosive medium. Curve B represents the group of materials where the corrosion rate increases rapidly at first and then decreases with increases in corrosive concentration. This is due to the 1. formation of the passive layer 2. decrease in the ionization of acids.
7. What is the corrosion rate behavior of curve A with the increase in corrosive concentration, described in the given figure?
a) Almost constant
b) Exponential increase
c) Exponential decrease
d) First increases and then decreases
Answer: a
Explanation: Curve A represents the group of materials in which an increase in corrosive concentrations has a negligible effect on it until very high concentrations are reached. This is due to the formation of the passive layer. After that, it results in mechanical damage at very high corrosive concentrations.
8. The concentration of the corrosive medium increases with the increase in impurity ion concentration.
a) True
b) False
Answer: a
Explanation: Concentration of corrosive medium depends on the concentration of impurity ions present in it. General impurities are dissolved oxygen, ferric ions, and many other metal oxides.
9. In which of the following reactions, we observe an increase in corrosion rate with the increase in corrosive concentration?
a) 18Cr–8Ni in HNO 3
b) Ni in NaOH
c) Pb in H 2 SO 4
d) Fe in H 2 SO 4
Answer: d
Explanation: Iron in sulfuric acid, the corrosion rate of iron increases at first and then it decreases with an increase in corrosive concentration. This is because, at low concentrations, iron will dissolve in sulfuric acid whereas at high concentrations it forms a passive layer on the sample surface.
Answer: b
Explanation: Nickel in caustic soda is the best corrosive resistant material at various corrosive concentrations. Thus, it shows a negligible change in the corrosion rate even with the increase in the corrosive concentration.
Sanfoundry Global Education & Learning Series – Corrosion Engineering.
This set of Corrosion Engineering Multiple Choice Questions & Answers focuses on “Principles – Effect of Galvanic Coupling”.
1. The effect of Galvanic Coupling is due to the contact of dissimilar metals in a conductive electrolyte.
a) True
b) False
Answer: a
Explanation: If two dissimilar metals are placed in contact with each other in a conductive electrolyte, the potential difference produces electron flow between them. This results in the acceleration of preferential anode dissolution. This is known as the effect of Galvanic coupling.
2. What are the factors that affect Galvanic coupling?
a) Type of metals
b) Relative size of electrodes
c) Environmental conditions
d) Types of metals, the relative size of electrodes and environmental conditions
Answer: d
Explanation: Metal combinations used for galvanic contact will affect based on the potential difference between them. Relative size of electrodes, environmental conditions such as temperature, humidity and salinity alter the chemical kinetics of the reaction.
3. Preferential cathode and anode are formed based on the potential value of a metal electrode.
a) True
b) False
Answer: a
Explanation: Electrode with relatively high reduction potential preferentially act as a cathode and the other electrode will act as an anode. The effect of galvanic coupling can be minimized by selecting metal combinations with less potential difference.
4. Which of the following type of corrosion is depicted in the given figure?
a) Uniform corrosion
b) Erosion corrosion
c) Galvanic corrosion
d) Crevice corrosion
Answer: c
Explanation: Galvanic corrosion is an electrochemical corrosion in which preferential anode will corrode rapidly due to the effect of galvanic coupling.
5. In which of the following cases, we observe the galvanic effect?
a) Bolts and Nuts metal joining’s
b) Piping arrangements
c) Machinery of a different metal combination
d) Bolts and nuts metal joining’s, piping arrangements and machinery of a different metal combinations
Answer: d
Explanation: The galvanic effect is due to the contact of two dissimilar metals in a conductive solution. The corrosion caused due to galvanic effect is known as galvanic corrosion. It can be usually observed at bolts and nuts metal joining’s, piping arrangements and machinery of different metal combinations.
6. What is the abbreviation of SHE?
a) Substitute hydrogen electrode
b) Standard hydrogen electrode
c) Significant hydrogen electrode
d) Standard hydride electrode
Answer: b
Explanation: SHE means a Standard hydrogen electrode. It is used to calculate the potential of other elements by arbitrarily defined as zero. The standard conditions of SHE is 1 atm pressure of H 2 gas, 25°C temperature and non-corroding conditions for pure metals.
7. Which of the following are Reference electrodes?
a) Standard hydrogen electrode
b) Calomel electrode
c) Silver electrode
d) Standard hydrogen electrode and a calomel electrode
Answer: d
Explanation: In EMF series all metals are referenced against the hydrogen electrode (H 2 /H+) which is arbitrarily defined as zero. This is known as the Standard hydrogen electrode . The saturated calomel electrode also acts as a reference electrode based on the reaction between elemental mercury and mercury chloride (Hg 2 Cl 2 ). And the electrode potential value of the calomel electrode is +0.241 V.
8. Which of the following is/are the characteristics of a Galvanic series?
a) Used only for pure metals
b) Less accurate prediction than EMF series
c) Includes active and passive potentials of a metal
d) Measured only at room temperature
Answer: c
Explanation: Galvanic series is the arrangement of various engineering materials in a decreasing reduction potential value in seawater. Galvanic series is more accurate than EMF series and it can be measured at various temperatures of a specific medium. It includes the active state potential and passive state potential of a metal.
9. Which of the following is/are the preventions of the galvanic effect?
a) Insulating dissimilar metals
b) Selection of close metal combinations in a galvanic series
c) Neglecting area effect
d) Insulating dissimilar metals and selection of close metal combinations in a galvanic series
Answer: d
Explanation: The galvanic effect is due to the contact of two dissimilar metals in a conductive solution. It can be minimized by insulating dissimilar metals with non-conductive materials. And it can be reduced by the selection of close metal combinations in a galvanic series.
10. Which of the following effect is described in the given figure?
a) Crevice
b) Pitting
c) Beneficial galvanic effect
d) Erosion
Answer: c
Explanation: The galvanic effect is due to the contact of two dissimilar metals in a conductive solution. Here beneficial galvanic effect takes place as zinc is corroding preferentially by protecting steel.
This set of Corrosion Engineering Questions and Answers for Experienced people focuses on “Principles – Metallurgical and Other Aspects”.
1. Which of the following are the types of materials, that are categorized based on its atomic arrangement?
a) Crystalline
b) Amorphous
c) Semi-crystalline
d) Crystalline, amorphous and semi-crystalline
Answer: d
Explanation: The atoms in the crystalline materials are regularly arranged with the same repeating unit in a long-range order. Examples of crystalline materials are metals.
The atoms in which the atoms are not regularly arranged over a long-range are called amorphous materials. Example: Glass, rubbers.
Whereas semi-crystalline is the combination of both crystalline and amorphous materials.
2. What is the crystal structure of Austenitic stainless steel?
a) Face centered cubic structure
b) Body-centered cubic structure
c) Hexagonal close packed structure
d) Simple cubic structure
Answer: a
Explanation: Austenitic stainless steel is an alloy of iron, chromium, and nickel. Due to the high content of chromium, the resultant stabilizes in the austenitic phase. Austenite usually exists in the FCC crystal structure.
3. What is the crystal structure of Magnesium?
a) Face centered cubic structure
b) Body-centered cubic structure
c) Hexagonal close packed structure
d) Simple cubic structure
Answer: c
Explanation: HCP is abbreviated as hexagonal close packed structure. Conditions for HCP is a 1 =a 2 ≠a 3 and α=β=60, Îł̈=120, where a 1 , a 2 , a 3 are unit vectors in three directions and α, β, Îł̈ are angles between them. Magnesium possesses an HCP crystal structure.
4. Which of the following crystal structure is depicted in the given figure?
a) Face centered cubic structure
b) Hexagonal close packed structure
c) Body-centered cubic structure
d) Simple cubic structure
Answer: c
Explanation: Simple cubic structure is a cube with lattice atoms only at the corners.
Face centered cubic structure is a cube with lattice atoms at the corners along with at the centers of cubic faces.
BCC is abbreviated as a Body-centered cubic structure. It is a cube with lattice atoms at the corner along with a single atom at the center of the cube.
5. Which of the following is/are the properties of metals?
a) Ductility
b) Electrical conductivity
c) Thermal conductivity
d) Ductility, electrical and thermal conductivity
Answer: d
Explanation:
Ductility, malleability, conductors of heat and electricity, lustrous, definite melting and boiling point, lustrous, high strength, sonorous, etc are the properties of metals.
6. Which of the following types of bonds are non-directional in nature?
a) Covalent bond
b) Ionic bond
c) Metallic bond
d) Covalent and metallic bond
Answer: d
Explanation: Non-directional bonding is a type in which each atom is bonded to many of its neighbors. Covalent and metallic bonds are non-directional in nature whereas ionic bond is directional in nature.
7. Grain boundaries are the mismatch regions formed between two grains during solidification.
a) True
b) False
Answer: a
Explanation: Every metal microstructure consists of grains and grain boundaries. Grain boundaries are high energy areas, formed due to the mismatch between the grains during the solidification.
8. Which of the following is an example of a homogenous alloy?
a) 18-8 stainless steel
b) Low carbon steel
c) High carbon steel
d) Spheroidal cast iron
Answer: a
Explanation: Homogenous alloy is the alloy in which the components are completely soluble in each other and it has only one phase. 18-8 stainless steel is a homogenous alloy with uniform composition and a single-phase structure.
9. Which of the following is an example of Heterogenous alloy?
a) High carbon steel
b) 18-8 stainless steel
c) Ni-Cu alloy
d) Bronze
Answer: a
Explanation: Heterogenous alloy is the alloy in which the components are partially dissolved in each other and it has two or more phases. High carbon steel consists of alpha iron, cementite phase, and lamellar structure.
10. Grain boundaries are highly prone to corrosion than the grain faces.
a) True
b) False
Answer: a
Explanation: Grain boundaries are the high energy area and are more active chemically. Hence, grain boundaries are highly prone to corrosion than the grain faces. This is used to develop a contrast between grain and grain boundaries in the inspection of microstructure.
11. Which of the following type of alloys are highly corrosion resistant in nature?
a) Homogenous alloys
b) Heterogenous alloys
c) Homogenous and heterogeneous alloys
d) Precipitation strengthened alloys
Answer: a
Explanation: Homogenous alloys are highly corrosion resistant alloys than other alloy types. Since the galvanic effect is not present in homogenous alloys because of its single phase.
12. Which of the following conditions are applied to the orthorhombic crystal structure?
a) a 1 =a 2 =a 3 and α=β=\
a 1 =a 2 ≠a 3 and α=β=\
a 1 ≠a 2 ≠a 3 and α=β=\
a 1 ≠a 2 ≠a 3 and α=β=\(\ddot{\gamma}\)≠90
Answer: c
Explanation: Crystal structures are divided into 14 different types based on the structure of the unit cell and arrangement of atoms in it. These 14 different types are called Bravais lattice. And the conditions for orthorhombic crystal structure is a 1 ≠a 2 ≠a 3 and α=β=Îł̈=90
, where a 1 , a 2 , a 3 are unit vectors in three directions and α, β, Îł̈ are angles between them.
13. Which of the following is the correct option regarding the packing efficiency of crystal structures?
a) FCC=HCP>BCC
b) FCC>HCP=BCC
c) FCC<BCC<HCP
d) HCP>FCC>BCC
Answer: a
Explanation: Packing efficiency = *100. Packing-efficiency of FCC, HCP, and BCC is 74%, 74%, and 68%. Therefore, the correct order is FCC=HCP>BCC.
14. What is the ROI in economic consideration of corrosion?
a) Refund on investment
b) Return on investment
c) Refund on income
d) Return on income
Answer: b
Explanation: ROI means Return on investment.
ROI=[(O a +I a /n a )–(O b +I b /n b )/I b –I a ]*100 where O = annual costs including maintenance cost, I=Investment, n=anticipated life in years, and subscripts a and b refer to the present and proposed installations, respectively.
15. What is NPV in economic consideration of corrosion?
a) Net profit volume
b) Net present value
c) Net profit value
d) Net precision value
Answer: b
Explanation: NPV provides the most accurate basis for analyzing business costs and can be directly applied to the economics of corrosion control. But it needs extensive calculations.
This set of Corrosion Engineering Multiple Choice Questions & Answers focuses on “Eight Forms – Uniform Corrosion”.
1. What is the important basis for the classification of corrosion?
a) Appearance of corroded metal
b) Nature of metal
c) Environmental conditions
d) Corrosion rate
Answer: a
Explanation: The basis for the classification of corrosion is the appearance of corroded metal. Each form can be identified by visual observation as it has a unique form of appearance.
2. Which of the following is/are types of corrosion?
a) Erosion corrosion
b) Galvanic corrosion
c) Pitting corrosion
d) Erosion, galvanic and pitting corrosion
Answer: d
Explanation:
Types of corrosion: i. Uniform corrosion
ii. Galvanic corrosion
iii. Crevice corrosion
iv. Pitting corrosion
v. Intergranular corrosion
vi. Selective leaching
vii. Erosion corrosion
viii. Stress corrosion
3. Which of the following type of corrosion is depicted in the given figure?
a) Pitting corrosion
b) Uniform corrosion
c) Erosion corrosion
d) Selective leaching
Answer: b
Explanation: Uniform corrosion is an electrochemical corrosion in which metal undergoes uniform depth of deterioration over its entire exposed surface. Example: Rusting of iron in atmospheric air.
4. Which of the following is an example of uniform corrosion?
a) Zinc dissolution in dilute H 2 SO 4
b) Dezincification of brass in acids
c) Rusting of iron
d) Zinc dissolution in dilute H 2 SO 4 and rusting of iron
Answer: d
Explanation: Uniform corrosion is characterized by an electrochemical reaction that proceeds uniformly over the entire exposed surface. Zinc dissolution in dilute H 2 SO 4 and rusting of iron are examples of uniform corrosion. Dezincification of brass in acids is an example of selective leaching.
5. Tarnishing of silver is an example of which type of corrosion?
a) Crevice corrosion
b) Pitting corrosion
c) Uniform corrosion
d) Erosion corrosion
Answer: c
Explanation: Outermost layers of silver undergoes a chemical reaction with hydrogen sulfide results in tarnish. This is known as the tarnishing of silver. Metals like brass, copper, aluminum, silver, and magnesium undergoes tarnishing under various corrosive environments.
6. What is/are the preventions of uniform corrosion?
a) Proper material coatings
b) Inhibitors
c) Cathodic protection
d) Proper material coatings, inhibitors, and cathodic protection
Answer: d
Explanation: Uniform corrosion can be prevented by proper material coatings, inhibitors, and cathodic protection. Proper material coatings minimize the exposure area of metal. An inhibitor is a chemical substance that decreases the corrosion rate of metal by modifying the surface of anode or cathode.
7. Which of the following is/are the causes of catastrophic failures of corrosion?
a) Incomplete weld penetration
b) Extremely porous casting
c) Improper heat treatment
d) Incomplete weld penetration, extremely porous casting and improper heat treatment
Answer: d
Explanation: Corrosion is an electrochemical reaction that results in the degradation of a material. Corrosion failures are usually catastrophic in nature. And the causes are incomplete weld penetration, extremely porous casting, and improper heat treatment.
8. What is the standard electrode potential of Fe +2 /Fe?
a) 0.0 V
b) +0.36
c) -0.44
d) -0.76
Answer: c
Explanation: Standard reduction potential of hydrogen ion, copper, iron, and zinc Is 0.0V, +0.36V, -0.44V and -0.76V respectively. These are measured against the standard hydrogen electrode which arbitrarily defined as zero.
9. Pure metals are more corrosion resistant than commercial materials.
a) True
b) False
Answer: a
Explanation: In most of the cases of corrosion, pure metals are more corrosion resistant than commercial materials. This is due to the absence of galvanic effect and selective leaching in pure metals.
10. Which of the following are the types of metallic coatings that prevent corrosion?
a) Metal cladding
b) Electroplating
c) Metal coat extrusion
d) Metal cladding, electroplating and metal coat extrusion
Answer: d
Explanation: Corrosion is an electrochemical reaction that results in the degradation of a material. It can be prevented by various metal coating methods such as metal cladding, electroplating and metal coat extrusion.
This set of Corrosion Engineering Multiple Choice Questions & Answers focuses on “Eight Forms – Galvanic Corrosion – 1”.
1.What is the other name of galvanic corrosion?
a) Bi-metallic corrosion
b) Mono-metallic corrosion
c) Localized corrosion
d) Mono-metallic and localized corrosion
Answer: a
Explanation: Galvanic corrosion can be termed as bi-metallic corrosion or two-metal corrosion. This is because the driving force for current transfer and corrosion is the potential developed between the two metals.
2. Corrosion of less corrosion-resistant metal is usually increased and the attack of the more corrosion-resistant is decreased in galvanic corrosion.
a) True
b) False
Answer: a
Explanation: As galvanic corrosion is a bi-metallic corrosion, relatively less corrosion-resistant metal preferentially acts as anode and relatively high corrosion-resistant metal preferentially acts as a cathode. This increases attack on the less corrosion-resistant metal and decreases on high corrosion-resistant metal .
3. Which of the following is the driving force in galvanic corrosion?
a) Conductivity of electrolyte
b) Crystal structure of metals
c) The potential difference between the two metals
d) Temperature of electrolyte
Answer: c
Explanation: The principle driving force for current transfer and corrosion is the potential developed between the two metals. This potential difference can be altered by various factors such as conductivity of electrolyte and temperature of the electrolyte.
4. Which of the following will act as cathode and anode respectively in a dry-cell battery?
a) Zinc and carbon
b) Carbon and zinc
c) Magnesium and zinc
d) Zinc and ammonium chloride
Answer: b
Explanation: Battery is a combination of cells in which chemical energy is converted into electrical energy. Carbon acts as cathode and zinc acts as an anode. Moist ammonium chloride is used as an electrolyte.
5. Which of the following is the primary characteristic of an electrolyte to form corrosion?
a) Electrical resistivity
b) Thermal resistivity
c) Thermal conductivity
d) Electrical conductivity
Answer: d
Explanation: Electrical conductivity is the primary characteristic of an electrolyte. Electrolyte is a medium to transfer electrons from anode to cathode, this results in corrosion. The conductivity of the electrolyte is one of the main factors in the regulation of corrosion.
6. What are the conditions to measure the standard reduction potential of metals against SHE?
a) 2 atm pressure, 25°C temperature, 2M concentration of H +
b) 2 atm pressure, 25°C temperature, 1M concentration of H +
c) 1 atm pressure, 25°C temperature, 1M concentration of H +
d) 1 atm pressure, 25°C temperature, 2M concentration of H +
Answer: c
Explanation: The conditions to measure the standard reduction potential of metal electrodes against standard hydrogen electrode are 1 atmospheric pressure, 25°C temperature and 1 molarity concentration of H + ions.
7. What is the standard reduction potential value of gold in the EMF series?
a) +1.498 V
b) +1.2 V
c) +0.987 V
d) +0.799 V
Answer: a
Explanation: Standard reduction potential values of metal are measured against SHE.
Standard reduction potential of gold (Au-Au +3 ), platinum (Pt-Pt +2 ), palladium (Pd-Pd +2 ), silver (Ag-Ag +1 ) are +1.498V, +1.2V, +0.987V and +0.799V respectively.
8. What is the standard reduction potential value of potassium in the EMF series?
a) +0.337 V
b) -2.925 V
c) -0.763 V
d) -1.662 V
Answer: b
Explanation: Standard reduction potential values of metal are measured against SHE, which is arbitrarily defined as zero. Standard reduction potential of potassium (K-K + ), aluminum (Al-Al +3 ), zinc (Zn-Zn +2 ), copper (Cu-Cu +2 ) are –2.925V, -1.662V, -0.763V and +0.337V respectively.
9. What is the abbreviation of EMF?
a) Electromagnetic force
b) Electromotive frequency
c) Electromotive force
d) Electrode motive force
Answer: c
Explanation: EMF is abbreviated as an electromotive force. It is defined as the potential difference between two points in a circuit. It is the cause of the flow of current in the circuit.
10. Which of the following electrolyte is used for the preparation of a general galvanic series?
a) Polluted seawater
b) Unpolluted river water
c) Polluted river water
d) Unpovlluted seawater
Answer: d
Explanation: Galvanic series is the most accurate prediction of galvanic relationships of metals. It is based on potential measurements and galvanic corrosion tests in unpolluted seawater. This includes metals and alloys along with their active and passive states.
11. Which of the following metal combination has a minimum galvanic effect?
a) Monel and copper
b) Inconel and Inconel
c) 18-8 stainless steel and 18-8 stainless steel
d) Titanium and lead
Answer: a
Explanation: The galvanic effect can be reduced by selecting close metal combinations. The position of a metal or an alloy in galvanic is mainly affected by its composition and its state . Monel and copper is the close metal combination, hence it has a minimum galvanic effect.
12. What does the square bracket [] in the galvanic series indicates?
a) Most practical metal combinations
b) High corrosion-resistant metals
c) Low corrosion-resistant metals
d) Avoidable metal combinations
Answer: a
Explanation: The bracket in the galvanic series indicates the most practical metal combinations. This metal combination results in little danger of galvanic corrosion.
Example: [ Monel, bronzes, copper, brasses]
13. The potential generated by two dissimilar metal combinations can change with time.
a) True
b) False
Answer: a
Explanation: The potential developed between two dissimilar metals is usually decreases. This is due to the accumulation of reaction or corrosion products at the anode or cathode. This results in a reduction of corrosion kinetics.
14. Which of the following is the most corrosion-resistant metal at room temperature?
a) Titanium
b) Platinum
c) Gold
d) Tantalum
Answer: d
Explanation: Tantalum is the most corrosion-resistant metal at room temperature. It is a rare, hard and lustrous transition metal. It is denoted by Ta and its atomic number is 73.
15. Which of the following corrosion is depicted in the given figure?
a) Crevice corrosion
b) Pitting corrosion
c) Galvanic corrosion
d) Uniform corrosion
Answer: c
Explanation: Voltaic cell is the cell in which chemical energy is converted into electrical energy by participating in redox reactions. In this cell, preferential cathode and anode are formed and the galvanic effect is observed. Thus, galvanic corrosion is depicted in the given figure.
This set of Corrosion Engineering Interview Questions and Answers for Experienced people focuses on “Eight Forms – Galvanic Corrosion – 2”.
1. The reason for the noble nature of titanium is that it cathodically polarizes readily in seawater.
a) False
b) True
Answer: b
Explanation: Titanium is one of the noble metals in the galvanic series and the reason is that it cathodically polarizes readily in seawater. It replaces many materials as best corrosive resistant metal in the seawater applications and high-velocity corrosive solutions.
2. Corrosion is greater near the seashore than in a dry rural atmosphere.
a) True
b) False
Answer: a
Explanation: Corrosion occurs due to the presence of oxygen and moisture . The electrical conductivity of the electrolyte is one of the factors of corrosion. Corrosion increases with an increase in electrical conductivity of the electrolyte. Moisture with salt content relatively has high electrical conductivity, hence corrosion is greater at the seashore.
3. Define the distance effect regarding galvanic corrosion?
a) Corrosion occurs only at the junction of two metals
b) Corrosion occurs only at the edges of two metals
c) Corrosion decreases with increase in distance from the junction
d) Corrosion increases with increase in distance from the junction
Answer: c
Explanation: The galvanic effect is the potential difference formed between two or more metals at its junction. It decreases on moving away from the junction. Hence corrosion decreases with an increase in distance from the junction.
4. Define area effect regarding galvanic corrosion?
a) cathodic area * anodic area
b) anodic area/cathodic area
c) cathodic area/anodic area
d) cathodic area + anodic area
Answer: c
Explanation: It is the ratio of cathodic to anodic areas. An unfavorable area ratio with a large cathodic area and small anodic area results in high current density at the anode. The greater the current density at an anodic area the greater the corrosion rate.
5. Which of the following is/are the preventions of galvanic corrosion?
a) Avoid the unfavorable area effect of a small anode and large cathode
b) Select the close combination of metals in galvanic series
c) Select the far combination of metals in galvanic series
d) Avoid the unfavorable area effect of a small anode and large cathode and select the close combination of metals in galvanic series
Answer: d
Explanation: In industrial applications avoiding a dissimilar metal combination is impossible. But it can be minimized by avoiding the unfavorable area effect, selecting the close combination of metals. Proper material selection and regular inspection are other preventive measures.
6. Which of the following principle is utilized in the concept of cathodic protection?
a) Principle of galvanic corrosion
b) Principle of crevice corrosion
c) Principle of pitting corrosion
d) Principle of selective leaching
Answer: a
Explanation: Cathodic protection is a protection of a base structure metal by making it as a cathode. It can be protected by the use of sacrificial anode. The order of metals in the galvanic series is the basis for cathodic protection.
7. Which of the following is an example of cathodic protection?
a) Electroplating of steel
b) Galvanization of steel
c) Magnesium connected to steel pipes
d) Electroplating of steel, galvanization of steel and magnesium connected to steel
Answer: d
Explanation: Electroplating and galvanization are cathodic protections of steel based on the galvanic effect. If steel under zinc or other metal coating exposed to corrosive atmosphere, zinc corrodes preferentially than steel. Magnesium acts as a sacrificial anode when it is connected to underground steel pipes.
8. Which of the following are the limitations of the EMF series?
a) Available for metals and alloys
b) Limited to pure metals only
c) Measured only at standard conditions
d) Limited to pure metals and measured only at standard conditions
Answer: d
Explanation: EMF series is a list of pure metals arranged according to their electrode potential value measured against SHE. It is measured at standard conditions such as 25°C, 1atm pressure, and 1M concentration of hydrogen ions.
9. Which of the following chemical is responsible for the stains on silver?
a) Hydrogen peroxide
b) Hydrogen sulfide
c) Sulfur dioxide
d) Sulfur trioxide
Answer: b
Explanation: The stains on sliver is usually due to the presence of hydrogen sulfide. It can be removed by the application of galvanic corrosion. It can be done with silver-aluminum galvanic attachment in the presence of baking soda.
10. Which of the following type of corrosion is depicted in the given figure?
a) Crevice corrosion
b) Pitting corrosion
c) Galvanic corrosion
d) Erosion corrosion
Answer: c
Explanation: Here zinc and iron preferentially act as the anode and cathode respectively. This is the galvanic effect. And zinc corrodes more rapidly and iron gets protected.
This set of Corrosion Engineering Multiple Choice Questions & Answers focuses on “Eight Forms – Crevice Corrosion”.
1. Which of the following is/are the reasons for the cause of crevice corrosion?
a) The stagnant solution in the holes and gasket surfaces
b) The stagnant solution in the lap joints and surface deposits
c) Dissimilar metal contact
d) The stagnant solution in the holes, gasket surfaces, lap joints, and surface deposits
Answer: d
Explanation: Crevice corrosion is a type of corrosion in which dissolution of metal is due to the presence of stagnant solution in the small gaps such as holes, gasket surfaces, lap joints, and surface deposits, etc.
2. Which of the following type of corrosion is localized in nature?
a) Crevice corrosion
b) Galvanic corrosion
c) Uniform corrosion
d) Inter-granular corrosion
Answer: a
Explanation: Crevice corrosion is localized corrosion because it occurs only at discrete sites on the metal surface. This occurs due to the presence of a stagnant solution in crevices . This crevice corrodes rapidly by cathodically protecting adjacent surfaces.
3. Which of the following is the other name of crevice corrosion?
a) Filiform corrosion
b) Deposit or gasket corrosion
c) Two-metal corrosion
d) Surface corrosion
Answer: b
Explanation: Crevice corrosion occurs due to the presence of a stagnant solution in the crevices. These crevices are formed due to the corrosion deposits or gaps at the metal-gasket interface. Thus, it is also called as deposit or gasket corrosion.
4. Which of the following metal is more susceptible to crevice corrosion?
a) Titanium
b) Hastelloy C
c) Stainless steel-430
d) Titanium and stainless steel
Answer: c
Explanation: Stainless steel-430 is highly prone to crevice corrosion. The reasons are as follows:
1. Large critical current density
2. Wide active-passive transitions
3. Limited passive region
5. Which of the following combination results in crevice corrosion?
a) Metal and absorbent gaskets
b) Continuous weld metals
c) Metal and non-absorbent gaskets
d) Single metal piece
Answer: a
Explanation: Metal and absorbent gasket combination results in the crevice corrosion. Absorbent gaskets absorb water vapor from surrounding and make them stagnant at the metal–gasket interface. This results in crevice corrosion.
6. Which of the following characteristics of the crevice is a must to act as a corrosion site?
a) It should be wide enough to permit liquid entry
b) It should be narrow enough to maintain a stagnant zone
c) It should be wide enough to avoid a stagnant zone
d) It should be wide enough to permit liquid entry and narrow enough to maintain a stagnant zone
Answer: d
Explanation: Crevice is a small volume region formed between the interface of metal and gaskets. It acts as a corrosion site if is wide enough to permit liquid entry and narrow enough to maintain a stagnant zone.
7. What is the primary condition regarding the velocity of an electrolyte to form crevice corrosion?
a) The velocity of the electrolyte should be greater than 10cm/s
b) The velocity of the electrolyte should be less than 10cm/s
c) The velocity of the electrolyte should be equal to 10cm/s
d) The stagnant electrolytic solution should be present
Answer: d
Explanation: Crevice corrosion occurs due to the presence of stagnant electrolytic solution in the crevices. It acts at the corrosion sites and it results in the formation of localized corrosion. An increase in the velocity of the electrolyte decreases the extent of crevice corrosion.
8. The difference in metal ion or oxygen concentration between the crevice and its surroundings is the main reason for crevice corrosion.
a) True
b) False
Answer: a
Explanation: Crevice corrosion is mainly occurred due to the difference in metal ion or oxygen concentration between the crevice and its surroundings. This is due to the unavailability of oxygen in the crevice, this results in the dissolution of metal in a crevice by protecting adjacent surface cathodically.
9. Which of the following chemical reaction that usually occurs in the crevice?
a) M + +H 2 O=MOH
b) M + +Cl – =MCl
c) M + Cl – +H 2 O=MOH +H + Cl –
d) 4OH – =O 2 +2H 2 O+4e –
Answer: c
Explanation: As the metallic ion concentration increases in the crevice, the migration of chloride ions takes place to neutralize that. After that, metal chlorides undergo hydrolysis and results in the formation of insoluble metal hydroxide and free acid.
10. Which of the following ions that accelerate the dissolution rate of metals or alloys in a crevice?
a) H + , OH –
b) H + , Cl –
c) OH – , Cl –
d) OH – , Cl – and H –
Answer: b
Explanation: H + and Cl – ions accelerate the dissolution rate of metals and alloys in the crevice. These are produced by hydrolysis of metal chlorides. It accelerates corrosion because hydrogen ion decreases pH value and chloride ion attacks the metallic surface in the crevice.
11. Which of the following metal is highly resistant to crevice corrosion?
a) Stainless steel
b) Copper
c) Aluminum
d) Hastelloy C-276
Answer: d
Explanation: Hastelloy C-276 is the best crevice corrosion-resistant metal. The composition of Hastelloy C-276 is 15.5%Cr, 54.7%Ni, 15.5%Mo, 3.8%W, and 0.5%Mn. Whereas the other metals depend on oxide film for their corrosion resistance.
12. As the metal dissolution within the crevice increases, the rate of oxygen reduction on adjacent surfaces increases.
a) True
b) False
Answer: a
Explanation: Metallic dissolution in the crevice cathodically protects the external surface. Electrons transfer from M==>M +n +ne to compensate O 2 +H 2 O+4e==>4OH .
13. What is the incubation period associated with a crevice attack?
a) 1 month – 10 months
b) 1 hour – 10 hours
c) 1 day – 10 days
d) 6 months – 1 year
Answer: d
Explanation: The incubation period is the time required to initiate the crevice corrosion on metal. It usually in the range of 6 months to 1 year. It depends on many factors such as the material used, corrosive medium, temperature, etc.
14. Metals or alloys that depend on oxide films for corrosive resistance are highly susceptible to crevice corrosion.
a) True
b) False
Answer: a
Explanation: Metals or alloys that depend on oxide films for corrosive resistance are highly susceptible to crevice corrosion. These passive films are destroyed by high concentrations of hydrogen and chloride ions, and the metallic dissolution increases rapidly.
15. Which of the following type of corrosion is depicted in the given figure?
a) Galvanic corrosion
b) Uniform corrosion
c) Crevice corrosion
d) Pitting corrosion
Answer: c
Explanation: Crevice corrosion is localized corrosion that occurs due to the formation of crevices on various metal or gasket junction. A crevice will act as a corrosion site when it is wide enough to permit liquid entry and narrow enough to maintain a stagnant zone.
This set of Corrosion Engineering Multiple Choice Questions & Answers focuses on “Eight Forms – Filiform Corrosion”.
1. Which of the following characteristics of active-passive metal will acquire optimize crevice corrosion resistance?
a) A narrow active-passive transition
b) A small critical current density
c) An extended passive region
d) A narrow active-passive transition, a small critical current density, and an extended passive region
Answer: d
Explanation: The optimum crevice corrosion resistance of active-passive transition metal is acquired by having the following characteristics: i. A narrow active-passive transition
ii. A small critical current density
iii. An extended passive region
2. Which of the following corrosion testing describe the test for crevice corrosion?
a) Occluded cell corrosion
b) Galvanic effect
c) Atmospheric exposure testing
d) Kesternich chamber testing
Answer: a
Explanation: Occluded cell corrosion is a corrosion testing that describes crevice corrosion. In this test, a narrow gap is maintained between two metal in a stagnant corrosive solution. An occluded cell is also known as crevice corrosion.
3. The incubation period is the amount of time required to initiate crevice corrosion on a corrosive site.
a) True
b) False
Answer: a
Explanation: The incubation period is the time required to initiate the crevice corrosion on a corrosive site. It depends on many factors such as
i. Type of crevice formed
ii. Nature of material used
iii. Temperature
iv. The difference in the concentration of oxygen in the crevice and its surroundings
4. The crevice corrosion index is an index is to assist the selection of materials for construction.
a) True
b) False
Answer: a
Explanation: Crevice corrosion index is developed by Streicher. CCI is an index used to assist the selection of materials for construction. It minimizes the chances of crevice formation by proper material selection.
5. Which of the following are the methods and procedures to minimize crevice corrosion?
a) Use of welded joints instead of riveted joints
b) Avoid sharp edges and stagnant areas
c) Removal of deposits frequently
d) Use of welded joints instead of riveted joints, avoid sharp edges and stagnant areas and removal of deposits frequently
Answer: d
Explanation: Combating or minimizing crevice corrosion can be done as follows:
l. Use of welded joints instead of riveted or bolted joints
ll. Avoid sharp edges and stagnant areas
lll. Regular inspection
lV. Removal of deposits frequently
V. Use of non-absorbent gaskets
6. Which of the following is a non-absorbent gasket?
a) Polyethylene
b) Isoprene
c) Teflon
d) Polyethylene and isoprene
Answer: c
Explanation: Teflon (CF 2 =CF 2 ) is a non-absorbent gasket. It is used in the industrial application to minimize the crevice corrosion. Whereas polyethylene and isoprene is absorbent to fluids such as water and acids.
7. Which of the following is also known as under film corrosion?
a) Crevice corrosion
b) Filiform corrosion
c) Galvanic corrosion
d) Pitting corrosion
Answer: b
Explanation: Filiform corrosion is a special type of crevice corrosion. It is also known as under film corrosion as it occurred under protective coatings or films. It usually seen on food and beverage cans.
8. Which of the following is/are the effects of filiform corrosion?
a) Weakens the metal
b) Decreases tensile strength
c) Affects surface appearance
d) Weakens the metal, decreases tensile strength and affects the surface appearance
Answer: c
Explanation: This filiform corrosion affects only surface appearance on metal-coated food and beverage cans that are exposed to the high humid atmosphere. It doesn’t weaken the metal as well as decreases the tensile strength.
9. Which of the following industry has major concern on filiform corrosion?
a) Petroleum industry
b) Canning industry
c) Automobile industry
d) Petroleum and automobile industry
Answer: b
Explanation: The Canning industry has a major concern on filiform corrosion. As canning is a preservation method by sealing the container’s airtightly and applying epoxy coating on the metal surface. Whereas the petroleum and automobile industry face uniform and galvanic corrosion as a major concern.
10. Which of the following ion/ions that result in the blue-green color of the active head in a corrosion filament?
a) Ferrous ions
b) Ferric oxide ions
c) Hydrated ferric oxide ions
d) Ferric oxide and hydrated ferric oxide ions
Answer: a
Explanation: A under film corrosion filament consists of an active head and inactive tail. The active head contains ferrous ions, that have a characteristic color of blue-green. Whereas inactive tail contains ferric oxide and hydrated ferric oxide ions, that has a characteristic color of red-brown.
11. Which of the following type of corrosion filament interaction is depicted in the given figure?
a) Reflection of corrosion filament
b) Splitting of corrosion filament
c) Joining of corrosion filament
d) Death trap of corrosion filament
Answer: d
Explanation: Since the growing filaments can’t cross inactive tails, they frequently get trapped and dies as the available space is decreased. This is known as the death trap.
12. Which of the following is the most environmental factor of filiform corrosion?
a) Relative humidity of the atmosphere
b) Temperature
c) pH of the environment
d) Temperature and pH of the environment
Answer: a
Explanation: Relative humidity of the surroundings is the most environmental factor of filiform corrosion. It occurs primarily between 65% to 90% relative humidity. If the relative humidity is less than 65%, the metal is unaffected.
13. What are the preventions of filiform corrosion?
a) Use of coatings with low water permeability
b) To store in low-humidity environment
c) To store in high-humidity environment
d) Use of coatings with low water permeability and to store in a low-humidity environment
Answer: d
Explanation: Filiform corrosion is a special type of crevice corrosion, occurs under metal coatings in a relatively high-humidity environment
Preventions to filiform corrosion:
i. Use of coatings with low water permeability
ii. To store in a low-humidity environment
iii. Use of brittle films or coatings
14. Which of the following type of corrosion is depicted in the given figure?
a) Crevice corrosion
b) Galvanic corrosion
c) Filiform corrosion
d) Uniform corrosion
Answer: c
Explanation: Here, the figure depicts the corrosion of steel under film or coating. This corrosion is called filiform corrosion and it is caused due to the relative humidity of the atmosphere.
This set of Corrosion Engineering Multiple Choice Questions & Answers focuses on “Eight Forms – Pitting Corrosion”.
1. Pitting is a form of extremely localized attack that results in holes in the metal.
a) True
b) False
Answer: a
Explanation: Pitting and crevice corrosion are the localized corrosion types, that results in the corrosion on very confined corrosive sites. Localized attack of pitting results in holes in the metal.
2. Which of the following is the characteristic of a pit?
a) Cavity with the surface diameter about the less than the depth
b) Cavity with the surface diameter about the same as or less than the depth
c) Cavity with the surface diameter about the same as or high than the depth
d) Cavity with the surface diameter about the high than the depth
Answer: b
Explanation: Pitting is extremely localized corrosion that results in pits or cavity. A pit is a cavity with the surface diameter about the same as or less than the depth.
3. Which of the following form of corrosion is more destructive and insidious in nature?
a) Uniform corrosion
b) Intergranular corrosion
c) Pitting corrosion
d) Galvanic corrosion
Answer: c
Explanation: Pitting is one of the most destructive and insidious forms of corrosion. It causes equipment to fail because of perforation with only a small percent weight loss of the entire structure.
4. Which of the following are the reasons that make it difficult to detect pits?
a) Small size
b) Varying depths
c) Pits covered with corrosion products
d) Small size, varying depths and covered with corrosion products
Answer: d
Explanation: It is difficult to measure the pitting quantitatively because of its small size, varying depth, and due to covered corrosion products. It fails the equipment because of perforation over the entire surface with only a small percent weight loss.
5. Which of the following metal is highly prone to pitting corrosion?
a) 18-8 stainless steel by sulfuric acid with FeCl 3
b) Titanium by sulfuric acid with FeCl 3
c) Nickel by sulfuric acid with FeCl 3
d) Copper by sulfuric acid with FeCl 3
Answer: a
Explanation: Pitting is one of the most destructive and insidious forms of corrosion. 18-8 stainless steel is highly prone to pitting corrosion by sulfuric acid in the presence of FeCl 3 . Whereas other metals are relatively resistant to pitting. Because it mainly depends on oxide film for its corrosion-resistant.
6. What is the usual direction for the growth of pits?
a) Vertically downwards
b) Vertically upwards
c) Horizontally sideward
d) Any primary direction
Answer: a
Explanation: Pits usually grow in the direction of gravity i.e. vertically downwards. Gravitational force holds the corrosive solution vertically downwards in a cavity, that makes the pit growth downwards. And very a smaller number of pits grown vertically upwards.
7. Pitting usually requires an incubation period ranges from months to years.
a) False
b) True
Answer: b
Explanation: Pitting can occur in two steps: i. Pit initiation ii. Pit growth.
The incubation period is the time required for a system to initiate pits on the metal surface. It usually ranges from months to years.
8. Which of the following corrosion form is depicted in the given figure?
a) Crevice corrosion
b) Uniform corrosion
c) Intergranular corrosion
d) Pitting corrosion
Answer: d
Explanation: Here, pitting corrosion is depicted in the figure. Pitting is extremely localized corrosion that results in pits or cavity and it is the most destructive and insidious form of corrosion.
9. Which of the following corrosion form is considered as the intermediate stage between uniform corrosion and complete corrosion resistance?
a) Galvanic corrosion
b) Pitting corrosion
c) Intergranular corrosion
d) Erosion corrosion
Answer: b
Explanation:
Case A: No corrosion of metal
Case B: Intense pitting on specific points
Case C: Uniform corrosion
10. Which of the following corrosion form is/are autocatalytic in nature?
a) Pitting and crevice corrosion
b) Crevice corrosion only
c) Pitting corrosion only
d) Pitting and intergranular corrosion
Answer: a
Explanation: Autocatalytic is a phenomenon of rapid corrosion that occurs within the pit or crevice, while oxygen reduction takes place on adjacent surfaces. This process is self-stimulating and self-propagating. It occurs in both pitting and crevice corrosion.
11. Which of the following statement is correct regarding pitting corrosion?
a) Adjacent surfaces cathodically protect pits
b) Pits cathodically protect adjacent surfaces
c) Neither pits nor adjacent surfaces protect each other
d) Both pits and adjacent surfaces protect each other
Answer: b
Explanation: Pits cathodically protect adjacent surfaces of metal; this is also called as cathodic protection. This is due to the autocatalytic nature of pitting corrosion. Hence, pits cathodically protect adjacent surfaces is the correct statement.
12. Which of the following is/are the difference between the crevice and pitting corrosion?
a) Autocatalytic nature
b) Corrosion mechanism
c) Initiation method
d) Both the corrosion mechanism and initiation method
Answer: c
Explanation: Pitting is a special case of crevice corrosion. But in the view of the initiation method, these two-corrosion processes are different. Pitting corrosion is a self-initiating corrosion form, whereas crevice corrosion needs the formation of crevice with differential concentration from outside.
13. Which of the following ions have a high tendency to pitting corrosion?
a) Chlorides
b) Bromides
c) Hypo chlorites
d) Chlorides, bromides, and hypochlorites
Answer: d
Explanation: In practical applications, most pitting failures are caused by chloride ions, hypochlorites, and bromide ions. Oxidizing metal ions with chlorides are aggressive pitters. Cupric, ferric, and mercuric halides are extremely aggressive.
14. Which of the following ions, that can reduce pitting corrosion?
a) Hydroxide salts
b) Chromate salts
c) Silicate salts
d) Hydroxide, chromate and silicate salts
Answer: d
Explanation: Pitting is one of the most destructive and insidious forms of corrosion. The tendency of pitting can be increased with the presence of chloride, bromide, and hypochlorites. But this tendency can be prevented or minimized with the presence of hydroxide, chromate, and silicate salts.
15. Which of the following corrosion test is most reliable to know the extent of pitting corrosion?
a) To measure the average depth of pits
b) To measure the maximum depth of a pit
c) Weight loss method
d) Weight gain method
Answer: b
Explanation: The measurement of maximum depth of pit would be a more reliable way of expressing pitting corrosion. As metal loss or metal gain is very small and does not indicate the depth of penetration.
This set of Corrosion Engineering Multiple Choice Questions & Answers focuses on “Eight Forms – Intergranular Corrosion – 1”.
1. Which of the following is/are more reactive in intergranular corrosion?
a) Grain
b) Grain boundary
c) Both grain and grain boundary
d) Neither grain nor grain boundary
Answer: b
Explanation: Intergranular corrosion occurs when grain interfaces or grain boundaries are very reactive than the face of grain. Whereas in the uniform attack, grains are more reactive than the grain boundaries.
2. What is Intergranular corrosion?
a) Localized attack at the grain boundaries
b) Localized attack at the grain faces
c) Uniform attack on grains
d) Localized attack at and adjacent to the grain boundaries
Answer: d
Explanation: Intergranular corrosion means corrosion in between two or more grains. Intergranular corrosion is a localized attack at and adjacent to the grain boundaries.
3. Which of the following is/are the causes of intergranular corrosion?
a) Impurities at the grain boundaries
b) Enrichment of one of the alloying elements at the grain boundary
c) Depletion of one of the alloying elements at the grain boundary
d) Impurities at the grain boundaries, enrichment, and depletion of one of the alloying elements at the grain boundary
Answer: d
Explanation: Intergranular corrosion is the corrosion occurs between two or more grains. It causes due to the presence of a differential concentration of alloying elements at the grains and grain boundaries. And the causes for this are as follows I. Presence of impurities at the grain boundaries
II. Enrichment of one of the alloying elements
III. Depletion of one of the alloying elements
4. Which of the following alloys is/are prone to intergranular corrosion?
a) Iron in aluminum
b) Zinc in brass
c) 18-8 Stainless steel
d) Iron in aluminum, zinc in brass and 18-8 stainless steel
Answer: d
Explanation: All the given alloys are prone to intergranular corrosion. Iron in aluminum and zinc in brass are susceptible to this corrosion, due to the segregation of iron and zinc respectively at the grain boundaries. Whereas 18-8 Stainless steel is susceptible due to the depletion of chromium at the grain boundaries.
5. Numerous failures of 18-8 Stainless steel have occurred in the temperature range of 950 to 1450°F
a) True
b) False
Answer: a
Explanation: Numerous failures of 18-8 stainless steel have occurred in the temperature range of 950 to 1450°F. When these steels are heated in the range of 950 to 1450°F they become sensitized or susceptible to intergranular corrosion due to the depletion of chromium at the grain boundary.
6. What is the molecular formula of chromium carbide formed due to the depletion of chromium in 18-8 stainless steel?
a) Cr 3 C
b) Cr 5 C 3
c) CrC
d) Cr 23 C 6
Answer: d
Explanation: Intergranular corrosion in 18-8 stainless steel is due to the depletion of chromium content at the grain boundary. This results in the formation of chromium carbide (Cr 23 C 6 ) at the grain boundary. Chromium depleted zone is highly prone to corrosion and it is known as intergranular corrosion.
7. Which of the following areas is/are corroded in the intergranular corrosion of stainless steel?
a) Grain only
b) Grain boundary only
c) Chromium depleted zone near the grain boundary
d) Both grain and grain boundary
Answer: c
Explanation: !8-8 stainless steel is susceptible to intergranular corrosion due to sensitization in the temperature of 950 to 1450°F. At this stage, chromium reacts with carbon near the grain boundary and results in the formation of the chromium depleted zone. This chromium depleted zone is prone to intergranular corrosion.
8. What is the minimum percent of chromium is needed to make stainless steel?
a) 2%
b) 20%
c) 1%
d) 11%
Answer: d
Explanation: Stainless steel is a family of iron-based alloys that contain a minimum of 11% chromium. Chromium imparts corrosive resistance to steel. There are 4 types of stainless steel.
They are i. Austenitic stainless steels
ii. Martensitic stainless steels
iii. Ferritic stainless steels
iv. Duplex stainless steels
9. Which of the following characteristics of the impoverished area, results in a rapid corrosion attack?
a) Less corrosion resistance
b) The high content of chromium
c) The large unfavorable area ratio
d) Less corrosion resistance and large unfavorable area ratio
Answer: d
Explanation: Rapid corrosion attack in impoverished or chromium depleted zone is due to
i. Less corrosion resistance
ii. Two dissimilar metal compositions are in contact
iii. Large unfavorable area ratio is present
10. Which of the following corrosion type is depicted in the given figure?
a) Intergranular corrosion
b) Galvanic corrosion
c) Crevice corrosion
d) Pitting corrosion
Answer: a
Explanation: Intergranular corrosion is the corrosion occurs between two or more grains. It causes due to the presence of a differential concentration of alloying elements at the grains and grain boundaries. Stainless steels are highly prone to this intergranular corrosion.
11. What is the structure of chromium carbide that precipitates at the grain boundaries?
a) Acicular structure
b) Leaflike structure
c) Lamellar structure
d) No specific structure
Answer: b
Explanation: Mahla and Nielsen of Du Pont, using the electron microscope, have shown that the carbides form on the envelope around the grains in a leaflike structure.
12. Which of the following term is associated with intergranular corrosion in welded structures?
a) Intergranular weld
b) Weld failure
c) Weld decay
d) Weld corrosion
Answer: c
Explanation: The intergranular corrosion associated with the welded structures and metals is known as weld decay. The depletion of alloying takes place adjacent to the weld bead as it exposed to high temperature .
13. Which of the following is used to visualize the heat flow and temperatures during welding?
a) Weld decay
b) Intergranular corrosion
c) Tablecloth analogy
d) Weld decay and intergranular corrosion
Answer: c
Explanation: Tablecloth analogy of heat flow and temperatures is used during welding. To visualize a mountain like a block with the rise and fall of each stripe represents the rise and fall of temperature in a welded plate.
14. Electric arc welding is used more than the gas welding for stainless steel to reduces the chances of weld decay.
a) True
b) False
Answer: a
Explanation: Welding time and the peak temperature of welding are the two parameters of weld decay. Electric arc welding produces more intense heat in a shorter time whereas in gas welding it is less intense and requires more time for welding.
15. Which of the following corrosives that induce intergranular corrosion in austenitic stainless steel?
a) Acetic acid
b) Acetic acid+salicylic acid
c) Ammonium nitrate
d) Acetic acid, acetic acid+salicylic acid, ammonium nitrate
Answer: d
Explanation: Stainless steel is highly susceptible to intergranular corrosion. These corrosives such as acetic acid, acetic acid+salicylic acid, ammonium nitrate, etc. Induces the intergranular corrosion in austenitic stainless steel.
This set of Corrosion Engineering Quiz focuses on “Eight Forms – Intergranular Corrosion – 2”.
1. Which of the following is/are the methods to control intergranular corrosion of austenitic stainless steel?
a) Employing solution-quenching
b) Adding stabilizers
c) Lowering the carbon content to below 0.03%
d) Employing solution-quenching, adding stabilizers and lowering the carbon content to below 0.03%
Answer: d
Explanation: Austenitic stainless steels are highly prone to intergranular corrosion. It can be minimized by
i. Employing quench-annealing or solution-quenching
ii. Adding stabilizers that forms strong carbides
iii. Lowering the carbon content to below 0.03%
2. Which of the following temperature range is required for commercial solution-quenching treatment?
a) 200°F-500°F
b) 800°F-1200°F
c) 1300°F-1700°F
d) 1950°F-2050°F
Answer: d
Explanation: Commerical solution-quenching treatment consists of heating to 1950°F to 2050°F followed by water quenching. Chromium carbide is dissolved at these temperatures, and a more homogenous alloy is formed. It minimizes the susceptibility of weld metal to weld decay.
3. Which of the following is/are the stabilizing elements to minimize intergranular corrosion of stainless steel?
a) Niobium
b) Columbium
c) Titanium
d) Niobium, columbium, and titanium
Answer: d
Explanation: Stabilizing elements are the elements that form strong carbides than chromium. These elements have a much greater affinity to carbon than does chromium, this minimizes the chromium depleted zone.
4. Which of the following region is indicated as BC in the given figure?
a) Weld bead
b) Heat affected zone
c) Weld decay
d) Neither weld decay nor bead
Answer: c
Explanation: Here in the given figure, region BC represents the weld decay zone and it is exposed to sensitizing temperature range during welding. This weld decay zone is highly susceptible to intergranular corrosion.
5. Carbon pickup during the production of austenitic stainless steels has caused premature failures of intergranular corrosion.
a) True
b) False
Answer: a
Explanation: Carbon pickup or surface carburization during the production of austenitic stainless steel has caused premature failures. It occurs when these steels are cast into molds that contain carbonaceous materials such as organic binders and baked oil sand. It reduces the corrosive resistance of these steels in the viewpoint of intergranular attack.
6. The intergranular attack is evident in the resin shell casting but not on the ceramic mold casting.
a) True
b) False
Answer: a
Explanation: Intergranular attack is evident in the resin shell casting but not on the ceramic mold casting. It is because of organic binders or organic content used for mold making in resin shell casting. It increases the surface carbon content of casting by the phenomenon known as carbon pickup.
7. What is the abbreviation of KLA regarding intergranular corrosion?
a) Knife-Line Attack
b) Knight-Line Attack
c) Knife-Life Action
d) Knight-Life Action
Answer: a
Explanation: KLA is abbreviated as Knife-Line Attack. Knife-Line Attack is similar to weld decay in that they both results from intergranular corrosion and both are associated with welding.
8. Which of the following is/are the characteristics of the Knife-line attack?
a) KLA occurs immediately adjacent to the weld
b) KLA occurs in the stabilized steels only
c) KLA occurs in the non-stabilized steels only
d) KLA occurs in the stabilized steels and it occurs immediately adjacent to the weld
Answer: d
Explanation: KLA occurs in a narrow band in the parent metal adjacent to weld and it occurs in the stabilized steels that are alloyed with niobium, titanium, and columbium.
9. Which of the following is the best remedy for the Knife-Line attack?
a) Heating the welded stabilized steel in the range of 950°F to 1400°F
b) Heating the welded stabilized steel in the range of 1400°F to 1900°F
c) Heating the welded stabilized steel to 1950°F
d) Heating the welded stabilized steel in the range of 1950°F to 2500°F
Answer: c
Explanation: The temperature range of 950°F to 1400°F is the sensitizing zone where only chromium carbide precipitates. Heating the welded stabilized steel to 1950 0 F results in the dissolution of chromium carbide and precipitation of columbium carbide.
10. Which of the following alloys exhibits intergranular corrosion by steam and marine atmospheres?
a) Die-cast zinc alloy
b) Duralumin alloy
c) Both die-cast zinc alloy and duralumin alloy
d) Neither die-cast zinc alloy nor duralumin alloy
Answer: a
Explanation: Die-cast zinc alloys containing aluminum exhibit intergranular corrosion by steam and marine atmosphere. Whereas duralumin alloys are also susceptible to intergranular corrosion in a different atmosphere.
This set of Corrosion Engineering Multiple Choice Questions & Answers focuses on “Eight Forms – Selective Leaching”.
1. Selective Leaching is the removal of one element from a solid alloy by the corrosion process.
a) True
b) False
Answer: a
Explanation: Selective leaching is one of the types of corrosion that results in the removal of one element from a solid alloy by the corrosion process. Dezincification, dealuminumification, and decobaltification are examples of selective leaching.
2. What is the percent of zinc that consists of common yellow brass?
a) 70%
b) 30%
c) 40%
d) 60%
Answer: b
Explanation: The composition of common yellow brass is approximately 30% zinc and 70% copper. Dezincification alloy assumes a red or copper color that contracts to the original yellow color.
3. Which of the following is/are the types of dezincification?
a) Layer-type
b) Plug-type
c) Layer-type and Plug-type
d) Neither Layer-type nor Plug-type
Answer: c
Explanation: There are two common types of dezincification types. They are
i. Layer-type or uniform
ii. Plug-type or localized
4. The Alloying of zinc to copper lowers the corrosion resistance of the copper.
a) True
b) False
Answer: a
Explanation: Alloying of zinc to copper lowers the corrosion resistance of the copper. The oxide film of copper is highly dense, stable, and has a high resistance to corrosion. Whereas zinc-copper alloy has a relatively less stable oxide film.
5. Which of the following is/are the characteristics of dezincified brass alloy?
a) Weak
b) Permeable
c) Porous
d) Weak, permeable and porous
Answer: d
Explanation: Dezincified brass alloy is an alloy in which the zinc is removed in a particular corrosive solution by selective leaching. Weak, permeable, and porous are the characteristics of dezincified brass alloy.
6. Which of the following type of brasses is/are highly prone to the uniform or layer-type dezincification?
a) Low brasses
b) High brasses
c) Low and high brasses
d) Neither high nor low brasses
Answer: b
Explanation: The composition of high brasses is usually 65% copper and 35% zinc. High brasses are highly prone to the uniform or layer-type dezincification in acidic environments.
7. Which of the following type of brasses is/are highly prone to localize or plug-type dezincification?
a) Low brasses
b) High brasses
c) Low and high brasses
d) Neither low nor high brasses
Answer: a
Explanation: The composition of low brasses are usually 80% copper and 20% zinc. Low brasses are highly prone to localize or plug-type dezincification in alkaline, neutral, and slightly acidic environments.
8. Which of the following is/are the preventions of dezincification?
a) Minimizing oxygen concentration
b) Use of less susceptible alloy
c) Adding a small amount of arsenic, antimony
d) Removal of oxygen concentration, use of less susceptible alloy and adding a small amount of arsenic, antimony
Answer: d
Explanation: Dezincification can be minimized or reduced by
i. Minimizing the oxygen concentration in the environment
ii. Use of less susceptible alloy such as red brass
iii. Adding small amounts of arsenic, antimony, and phosphorus as an inhibitor
9. Which of the following phenomenon that results in the dissolution of iron by leaving porous graphite on the surface of grey cast iron?
a) Dezincification
b) Decalcification
c) Graphitization
d) Dezincification and graphitization
Answer: c
Explanation: Graphite is cathodic to iron in grey cast iron that results in the dissolution of iron by leaving porous graphite in a mild corrosive solution. This phenomenon is known as graphitization.
10. Which of the following type of cast irons that exhibits graphitization?
a) Grey cast iron
b) Nodular cast iron
c) Malleable cast iron
d) Grey cast iron, nodular cast iron, and malleable cast iron
Answer: a
Explanation: Graphitization occurs only in grey cast iron whereas it doesn’t occur in nodular, malleable, and white cast iron as the graphite network is not present to hold together at the surface.
11. Which of the following acid that results in selective removal of aluminum in aluminum bronzes?
a) Hydrochloric acid
b) Hydrofluoric acid
c) Nitric acid (HNO 3 )
d) Hydrochloric, hydrofluoric and nitric acid
Answer: b
Explanation: Selective Leaching is the removal of one element from a solid alloy by the corrosion process. And selective removal of aluminum from aluminum bronzes can be resulted by using hydrofluoric acid.
12. Which of the following is/are the other names of selective leaching?
a) Dealloying
b) Parting
c) Dealloying and parting
d) Neither dealloying nor parting
Answer: c
Explanation: Selective Leaching is the removal of one element from a solid alloy by the corrosion process. The other names of selective leaching are dealloying and parting.
13. Which of the following is/are the benefits of selective leaching?
a) Enrichment of silicon on stainless steel for better passivity
b) Preparation of Raney nickel catalyst
c) Extraction of metals using hydrometallurgy
d) Enrichment of silicon on stainless steel for better passivity, preparation of Raney nickel catalyst and extraction of metals using hydrometallurgy
Answer: d
Explanation: The benefits associated with selective leaching are
i. Enrichment of silicon on Stainless steel for better passivity
ii. Preparation of Raney nickel catalyst
iii. Extraction of metals using hydrometallurgy
14. Which of the following type of corrosion is depicted in the given figure?
a) Galvanic corrosion
b) Uniform corrosion
c) Selective leaching
d) Erosion corrosion
Answer: c
Explanation: Selective Leaching is the removal of one element from a solid alloy by the corrosion process. And in selective leaching, it is a layer or uniform type of zincification. It highly occurs in high brasses that contain 35% zinc approximately.
This set of Corrosion Engineering Multiple Choice Questions & Answers focuses on “Eight Forms – Erosion Corrosion”.
1. Erosion corrosion accelerates the rate of attack on a metal because of relative movement between corrosive fluid and the metal surface.
a) True
b) False
Answer: a
Explanation: Erosion corrosion is one of the types of corrosion that accelerates the rate of deterioration or attack on a metal because of the relative movement of corrosive fluid and the metal surface.
2. Which of the following type of directional patterns usually exhibit by erosion-corrosion?
a) Grooves
b) Waves
c) Rounded holes
d) Grooves, waves and rounded holes
Answer: d
Explanation: Erosion corrosion results in wear or abrasion of the surface of the metal. It is characterized in appearance by grooves, gullies, waves, rounded holes, and valleys.
3. Which of the following type of corrosion is depicted in the given figure?
a) Uniform corrosion
b) Erosion corrosion
c) Galvanic corrosion
d) Selective leaching
Answer: b
Explanation: Erosion corrosion is depicted in the given figure. Erosion corrosion accelerates the rate of deterioration or attack on a metal because of the relative movement of corrosive fluid and the metal surface.
4. Erosion corrosion results when the protective oxide films are damaged and the metal or alloy are attacked at a rapid rate.
a) True
b) False
Answer: a
Explanation: As the relative movement of the corrosive solution and the surface of the metal increases the intensity of erosion-corrosion increases. At higher velocities, it results in the damage or worn out of oxide film and it attacks the metal rapidly.
5. Which of the following metals is/are susceptible to erosion-corrosion?
a) Aluminum
b) Lead
c) Stainless steel
d) Aluminum, lead and stainless steel
Answer: d
Explanation: Aluminum, lead, copper, and stainless steel are the metals that are susceptible to erosion-corrosion. Because these metals mainly depend on their oxide film for its corrosive resistance.
6. Which of the following type of equipment is/are highly prone to erosion-corrosion?
a) In piping arrangements at elbows and bends
b) Measuring devices such as orifice and turbine blades
c) In piping arrangements at straight lines
d) In piping arrangements at elbows and bends and measuring devices such as orifice and turbine blades
Answer: d
Explanation: Erosion corrosion can be affected by the relative velocity of the corrosive solution and metal surface and along with impingement velocity at the edges and turnings. In piping arrangements at elbows and bends and measuring devices such as orifice and turbine blades are the equipment that is prone to erosion-corrosion.
7. Which of the following is/are the characteristics of oxide film that exhibits better resistance to erosion-corrosion?
a) Hard
b) Dense
c) Adherent
d) Hard, dense and adherent
Answer: d
Explanation: Erosion corrosion is the type of corrosion that results in mechanical damage of the metal due to the high velocities of corrosive solutions. And a hard, dense, and adherent oxide film can exhibit better resistance to erosion-corrosion.
8. Which of the following characteristics of titanium, makes it resistant to erosion-corrosion?
a) Stability of titanium oxide
b) Instability of titanium oxide
c) The low reactivity of titanium
d) The low reactivity of titanium and instability of titanium oxide
Answer: a
Explanation: Titanium is a reactive metal but is resistant to erosion-corrosion in many environments because of the stability of the titanium oxide (TiO 2 ) film. It reforms its oxide layer within a fraction of seconds after wearing out.
9. Which of the following metal is resistant to seawater, chlorides, and fuming nitric acid?
a) Aluminum
b) Lead
c) Titanium
d) Stainless steel
Answer: d
Explanation: Titanium is highly resistant to seawater, chlorides, and fuming nitric acid. It is also resistant to erosion-corrosion because of its high reactivity and stability of oxide film.
10. Which of the following environmental factor plays an important role in erosion-corrosion?
a) Velocity
b) Corrosive concentration
c) pH of the environment
d) Relative humidity of the atmosphere
Answer: a
Explanation: Erosion corrosion accelerates the rate of attack on a metal because of relative movement between corrosive fluid and the metal surface. It increases as the velocity of the corrosive solution increases.
11. Define critical velocity regarding erosion-corrosion.
a) Velocity at which erosion-corrosion starts
b) Velocity at which erosion-corrosion stops
c) Velocity after which erosion-corrosion increases exponentially
d) Velocity after which erosion-corrosion decreases exponentially
Answer: c
Explanation: Critical velocity is the velocity after which the erosion-corrosion increases exponentially. Case 1 :
Erosion corrosion increases linearly with increase with velocity.
Case 2 :
Erosion corrosion increases exponentially with increase with velocity.
12. Which of the following metal shows a decrease in corrosion attack with an increase in velocity in fuming nitric acid?
a) Aluminum
b) Carbon steel
c) Stainless steel 347
d) Copper
Answer: c
Explanation: Under stagnant conditions, stainless steel 347 in nitric acid is attacked autocatalytically because of the formation of nitrous acid as a cathodic reaction product. An increase in velocity sweeps away the corrosive nitrous acid in the environment.
13. Which of the following is/are the preventions of erosion-corrosion?
a) Selection of better resistant materials
b) Alteration of the environment
c) Applying protective coatings
d) Selection of better resistant materials, alteration of the environment and applying protective coatings
Answer: d
Explanation: Methods for minimizing or preventing erosion-corrosion
i. Selection of better resistant materials
ii. Design of equipment
iii. Alteration of environment
iv. Applying protective coatings
v. Cathodic protection of equipment.
14. Which of the following is/are the aspects of design to minimize erosion-corrosion?
a) Increasing pipe diameter
b) Avoiding sharp edges and turnings
c) Readily replaceable impingement plates should be inserted
d) Increasing pipe diameter, avoiding sharp edges and turnings and readily replaceable impingement plates should be inserted
Answer: d
Explanation: Design is an important factor to minimize or combat erosion-corrosion. The design includes increasing pipe diameter, avoiding sharp edges and turnings, readily replaceable impingement plates should be inserted, and maintaining certain angles to minimize impingement area.
15. Which of the following is/are the aspects of alteration of the environment to minimize erosion-corrosion?
a) Deaeration of corrosive solution
b) Decrease the temperature
c) Use of Settling and filtration to remove suspended solids
d) Deaeration of the corrosive solution, decrease the temperature and use of settling and filtration to remove suspended solids
Answer: d
Explanation: Alteration of the environment is also one of the methods to minimize erosion-corrosion. This includes the deaeration of corrosive solution, decrease the temperature and use of settling and filtration to remove suspended solids.
This set of Corrosion Engineering MCQs focuses on “Eight Forms – Cavitation and Fretting Corrosion”.
1. Which of the following type of corrosion is caused by the formation and collapse of vapor bubbles in a liquid near the metal surface?
a) Filiform corrosion
b) Fretting corrosion
c) Cavitation damage
d) Crevice corrosion
Answer: c
Explanation: Cavitation damage is the special form of erosion-corrosion that occurs by the formation and collapse of vapor bubbles in a liquid near a metal surface.
2. Which of the following equipment encounters cavitation damage in the service?
a) Hydraulic turbines
b) Ship propellers
c) Pump impellers
d) Hydraulic turbines, ship propellers, and pump impellers
Answer: d
Explanation: Cavitation damage occurs in hydraulic turbines, ship propellers, pump impellers, and other surfaces where high-velocity liquid flow and pressure changes are encountered.
3. Which of the following condition is/are correct regarding the boiling point of a liquid with an increase in pressure?
a) Decreases up to triple point
b) Increases up to triple point
c) Increases up to the critical point
d) Decreases up to the critical point
Answer: a
Explanation: As the pressure of a liquid decreases, its boiling point decreases up to its triple point. As the pressure increases its increases up to a critical point.
Example: At higher altitudes boiling point of liquids reaches low as atmospheric pressure decreased.
4. Which of the following will result due to cavitation damage of a metal?
a) Mechanical action
b) Chemical dissolution
c) Both mechanical action and chemical dissolution
d) Neither mechanical action nor chemical dissolution
Answer: c
Explanation: Cavitation damage is the special form of erosion-corrosion that occurs by the formation and collapse of vapor bubbles in a liquid near a metal surface. It results in the mechanical and chemical dissolution of metal.
5. Cavitation damaged can be reduced by changing the design to minimize hydrodynamic pressure differences in process streamflow.
a) False
b) True
Answer: b
Explanation: Cavitation damaged can indeed be reduced by changing the design to minimize hydrodynamic pressure differences in process streamflow. It reduces the impingement area and force of the stream.
6. Which of the following type of corrosion is depicted in the given figure?
a) Fretting corrosion
b) Crevice corrosion
c) Cavitation damage
d) Pitting corrosion
Answer: c
Explanation: Cavitation damage is depicted in the given figure. It occurs by the formation and collapse of vapor bubbles in a liquid near a metal surface. And it results in mechanical action and chemical dissolution of metal.
7. Which of the following type of corrosion that occurs at contact areas between materials under load subjected to vibration or relative motion?
a) Fretting corrosion
b) Crevice corrosion
c) Cavitation damage
d) Pitting corrosion
Answer: a
Explanation: Fretting corrosion is the special type of erosion-corrosion that occurs at the contact areas between materials under load subjected to vibration or relative motion.
8. Which of the following is/are the other names of fretting corrosion?
a) Friction oxidation
b) Wear oxidation
c) False brinelling
d) Friction oxidation, wear oxidation and false brinelling
Answer: d
Explanation: Fretting corrosion is one of the special types of erosion-corrosion. It also called friction oxidation, wear oxidation, chafing, and false brinelling. Because it gets initiated with wear or friction and oxides debris are formed during corrosion.
9. Which of the following is/are the classic cases of fretting corrosion?
a) Bolted tie plates on railroad rails
b) Press-fitted ball bearing race on a shaft
c) On ball bearings
d) Bolted tie plates on railroad rails and press-fitted ball bearing race on a shaft
Answer: d
Explanation: Fretting corrosion occurs at contact areas between materials under load subjected to vibration or repeated relative motion. And it doesn’t occur on materials in continuous motion such as on ball bearings.
10. Which of the following is/are the basic requirements for the occurrence of fretting corrosion?
a) The interface must be under load
b) Vibration or repeated relative motion between the two surfaces
c) The interface must be under load and vibration or repeated relative motion between the two surfaces
d) The relative motion should be high
Answer: c
Explanation: The basic requirements for the occurrence of fretting corrosion are:
i. The interface must be under load
ii. Vibration or repeated relative motion between the two surfaces
iii. The load and the relative motion of the interface must be sufficient to produce deformation.
11. Which of the following is/are the preventive measures of fretting corrosion?
a) Lubricate with low-viscosity, high-tenacity oil
b) Increasing surface hardness by shot-peening or cold working
c) Use gaskets to absorb vibrations
d) Lubricate with low-viscosity, high-tenacity oil, increasing surface hardness by shot-peening and use gaskets to absorb vibrations
Answer: d
Explanation: Preventive measures to minimize fretting corrosion:
i. Lubricate with low-viscosity, high-tenacity oil, and greases
ii. Increasing surface hardness by shot-peening or cold working
iii. Use gaskets to absorb vibrations and exclude oxygen at bearing surfaces
iv. Increase the load to decrease slip between two metals.
This set of Corrosion Engineering Multiple Choice Questions & Answers focuses on “ Eight Forms – Stress Corrosion”.
1. What is the abbreviation of SCC regarding corrosion?
a) Stress-corrosion cracking
b) Stress-cracking corrosion
c) Stress-corrosion contact
d) Stress-contact corrosion
Answer: a
Explanation: SCC can be abbreviated as stress-cracking corrosion. It is referred to the simultaneous action of corrosion and stress on a metal structure. Tensile stress is the most common stress that encounters in the industrial world.
2. Stress-corrosion cracking occurs due to the simultaneous presence of tensile stress and a specific corrosive medium.
a) True
b) False
Answer: a
Explanation: Stress–corrosion cracking occurs due to the simultaneous presence of tensile stress either is caused by residual or external stress and a specific corrosive medium. Residual stress is caused due to welding, cold working, etc.
3. Which of the following is/are the classic examples of stress-corrosion cracking?
a) Season cracking of brass
b) Caustic embrittlement of steel
c) Season cracking of brass and caustic embrittlement of steel
d) Neither season cracking of brass nor caustic embrittlement of steel
Answer: c
Explanation: The two main classic examples of stress-corrosion cracking are:
i. Season cracking of brass
ii. Caustic embrittlement of steel.
4. What is meant by season cracking of brass?
a) Stress-corrosion cracking failure of brass cat ridge cases due to ammonia
b) Stress-corrosion cracking failure of brass cat ridge cases due to caustic soda
c) Stress-corrosion cracking failure of brass cat ridge cases due to caustic soda and ammonia
d) Stress-corrosion cracking failure with brittle fracture
Answer: a
Explanation: Season cracking refers to the stress-corrosion cracking failure of brass cat ridge cases. The main important environmental component in season cracking is ammonia, which results from the decomposition of organic matter.
5. What is meant by caustic embrittlement of steel?
a) Failure of cold-worked rivets by a brittle fracture in the presence of ammonia
b) Failure of cold-worked rivets by a brittle fracture in the presence of caustic soda
c) Failure of cold-worked rivets by a brittle fracture in the presence of caustic soda and ammonia
d) Failure of cold-worked rivets by the cup and cone fracture in the presence of caustic soda
Answer: b
Explanation: Explosions of riveted boilers that occurred in early steam-driven locomotives are due to the cold working during the operation. Hence, brittle fracture in the presence of caustic resulted in caustic embrittlement.
6. In which of the following environments that stainless steel will undergo stress-corrosion cracking?
a) Chlorides
b) Caustics
c) Ammonia
d) Chlorides and caustics
Answer: d
Explanation: Stainless steel undergoes stress-corrosion cracking in chlorides and caustics. They do not crack in ammonia, sulfuric acid, nitric acid, acetic acid, and pure water.
7. Which of the following is/are the most important variables that affect stress-corrosion cracking?
a) Temperature
b) Metal composition
c) Type and amount of stress applied
d) Temperature, metal composition, and type and amount of stress applied
Answer: d
Explanation: The most important variables that affect stress-corrosion cracking are:
i. Temperature
ii. Metal composition
iii. Corrosive solution composition
iv. Type and amount of stress applied
v. Design of metal structure.
8. Which of the following alloy in which both intergranular and trans-granular cracking occurs?
a) High-nickel alloys
b) iron-chromium alloys
c) Brasses
d) High-nickel alloys, iron-chromium alloys, and brasses
Answer: d
Explanation: Stress-corrosion cracking can be intergranular and trans-granular cracking. Alloys such as high-nickel alloys, iron-chromium alloys, and brasses often crack both in intergranular and transgranular manner.
9. Define Threshold stress regarding stress-corrosion cracking.
a) The maximum stress at which the specimen ruptures
b) The maximum stress required to prevent cracking
c) The minimum stress required to prevent cracking
d) The minimum stress at which cracking starts
Answer: c
Explanation: Increasing stress decreases the time before cracking occurs. Threshold stress is the minimum stress required to prevent cracking. It depends on temperature, alloy composition, and environment composition.
10. As stress-corrosion cracks penetrate the material, the cross-sectional area gets reduced under constant tensile load.
a) False
b) True
Answer: b
Explanation: Stress-corrosion cracking is the simultaneous attack of corrosion and stress. A stress-corrosion crack penetrates the material; the cross-sectional area gets reduced under constant tensile stress.
11. Which of the following is/are the environments that cause stress-corrosion cracking to titanium?
a) Red fuming nitric acid
b) Methanol-HCl
c) Nitrogen tetroxide (N 2 O 4 )
d) Red fuming nitric acid, methanol-HCl, and nitrogen tetroxide
Answer: d
Explanation: Stress-corrosion cracking is the simultaneous action of stress and corrosive environment on a metal. Red fuming nitric acid, methanol-HCl, and nitrogen tetroxide are the environments that may cause stress-cracking corrosion.
12. Which of the following is/are the metallurgical factors that affect stress-corrosion cracking?
a) Chemical composition
b) Distribution of precipitates
c) Dislocation interactions
d) Chemical composition, distribution of precipitates and dislocation interactions
Answer: d
Explanation: Metallurgical factors that affect stress-corrosion cracking are:
i. Average chemical composition
ii. Preferential orientation of grains
iii. Distribution of precipitates
iv. Dislocation interactions
v. Degree of metastability.
13. Which of the following type of stress has an important role in rupturing protective films during both the initiation and propagation of cracks?
a) Tensile stress
b) Compressive stress
c) Shear stress
d) Compressive and shear stress
Answer: a
Explanation: Tensile stress has an important role in rupturing protective films during both the initiation and propagation of cracks. Breaks in the passive layer of metal induce a rapid attack.
14. Which of the following stress-corrosion cracking mechanism is highly acceptable?
a) Dissolution mechanics
b) Mechanical mechanics
c) Both dissolution and mechanical mechanics
d) Hydrogen mechanics
Answer: a
Explanation: Dissolution mechanics is highly acceptable than mechanical mechanics. The dissolution model describes anodic dissolution at the crack tip, as strain ruptures the passive film at the tip.
15. Which of the following is/are the preventions of stress-corrosion cracking?
a) Lowering working stress below the threshold value
b) Shot peening to produce residual compressive stresses
c) Applying for cathodic protection
d) Lowering working stress below the threshold value, shot peening to produce residual compressive stresses and applying for cathodic protection
Answer: d
Explanation: Methods to prevent stress-corrosion cracking are:
i. Lowering working stress below the threshold value
ii. Shot peening to produce residual compressive stresses
iii. Applying cathodic protection to the structure
iv. Adding inhibitors to the system
v. Eliminating the critical environment species.
This set of Corrosion Engineering Multiple Choice Questions & Answers focuses on “Eight Forms – Corrosion Fatigue”.
1. Corrosion fatigue is defined as the reduction of fatigue resistance due to the presence of a corrosive medium.
a) True
b) False
Answer: a
Explanation: Corrosion fatigue is a simultaneous action of corrosion and fatigue on a metal. It is defined as the reduction in fatigue resistance due to the presence of a corrosive medium.
2. What is meant by fatigue?
a) The tendency of a metal to fracture under static loading
b) The tendency of a metal to fracture under repeated cyclic loading
c) The tendency of a metal to fracture under non-repeating cyclic loading
d) The tendency of a metal to fracture after heavy deformation
Answer: b
Explanation: Fatigue is defined as the tendency of a metal to fracture under repeated cyclic loading. Bridges, machines will usually fail due to fatigue. It fails the metals even below the yield stress of that metal due to repeated cyclic loading.
3. What is the nature of fatigue fracture?
a) Brittle fracture
b) Cup and cone fracture
c) Tensile fracture
d) Brittle and tensile fracture
Answer: a
Explanation: A fatigue crack propagates until the cross-sectional area of the metal is reduced to the point where the ultimate strength is exceeded and rapid brittle fracture occurs. The nature of fatigue fracture is brittle.
4. Which of the following type of corrosion is depicted in the given figure?
a) Cavitation damage
b) Fretting corrosion
c) Corrosion fatigue
d) Uniform corrosion
Answer: c
Explanation: Corrosion fatigue is defined as the simultaneous effect of corrosion and fatigue on a metal. A fatigue crack propagates until the cross-sectional area of the metal is reduced to the point where the ultimate strength is exceeded and rapid brittle fracture occurs. And the other part experience corrosion.
5. Define the fatigue limit of a metal.
a) Stress below which metal will endure an infinite number of cycles without fracture
b) Stress above which metal will endure an infinite number of cycles without fracture
c) Stress at which metal will endure a less finite number of cycles
d) Stress at which metal will endure a more finite number of cycles
Answer: a
Explanation: Fatigue limit is the stress below which metal will endure an infinite number of cycles without fracture. The fatigue limit can be calculated by stress and the number of cycles curve.
6. Which of the following metal is depicted by curve A of given SN graph?
a) Aluminum
b) Tungsten
c) Steel
d) Calcium
Answer: a
Explanation: The given figure is an SN curve with the stress of the y-axis and the number of cycles on the x-axis. Curve A depicts the SN curve of nonferrous metals such as aluminum, copper, and nickel. Fatigue resistance for these metals increases with decreases in stress applied.
7. Which of the following metal is depicted in curve B of a given SN graph?
a) Aluminum
b) Copper
c) Steel
d) Zinc
Answer: c
Explanation: Ferrous alloys exhibit an increase in fatigue resistance with a decrease in stress, after that, it remains independent of stress applied. This point is known as the fatigue limit of the metal. It is defined as the stress below which the metal will endure an infinite number of cycles without fracture.
8. Which of the following is/are the factors that influence corrosion fatigue?
a) Type of metal
b) Composition of corrosive solution
c) Temperature
d) Type of metal, corrosive solution composition, and temperature
Answer: d
Explanation: The factors that influence corrosion fatigue:
• Type of metal
• Composition of corrosive solution
• Temperature
• PH of the environment
• Percentage of oxygen content.
9. Which of the following is/are the facts that indicate the reduction in fatigue resistance of metal?
a) Corrosion pits act as stress raisers
b) Corrosion pits act as initiate cracks
c) Corrosion pits act as a stress raiser and initiate cracks
d) Corrosion pits neither act as stress raiser nor initiate cracks
Answer: c
Explanation: Corrosion fatigue is the combination of both corrosion and fatigue simultaneously. Fatigue resistance is reduced because corrosion pits act as stress raisers and initiate cracks.
10. Which of the following is/are the preventions of corrosion fatigue?
a) Use of high tensile strength metals
b) Perform shot penning to induce compressive stresses
c) Use coatings such as electrodeposited zinc, nickel
d) Use of high tensile strength metals, perform shot penning to induce compressive stresses and use of coatings such as electrodeposited zinc, nickel
Answer: d
Explanation: Methods to prevent corrosion fatigue:
• Use of high tensile strength metals
• Perform shot penning to induce compressive stresses
• Use coatings such as electrodeposited zinc, nickel, chromium, copper and nitride coatings.
This set of Corrosion Engineering Multiple Choice Questions & Answers focuses on “Eight Forms – Hydrogen Damage”.
1. Hydrogen damage refers to the mechanical damage of a metal caused by the presence of or interaction of hydrogen.
a) True
b) False
Answer: a
Explanation: Hydrogen damage refers to the mechanical damage of a metal caused by the presence of or interaction of hydrogen. And hydrogen damage can be classified into four types based on the mechanism of failure.
2. Which of the following is/are the types of hydrogen damage?
a) Hydrogen blistering
b) Hydrogen embrittlement
c) Decarburization
d) Hydrogen blistering, hydrogen embrittlement, and decarburization
Answer: d
Explanation: Classification of hydrogen damage:
Hydrogen blistering
Hydrogen embrittlement
Decarburization
Hydrogen attack.
3. What is meant by hydrogen blistering?
a) Entrapment of hydrogen molecules in the metal voids
b) Formation of brittle metal hydrides
c) Entrapment of metal hydrides in the metal voids
d) Entrapment of hydrogen molecules and metal hydrides in the metal voids
Answer: a
Explanation: Hydrogen blistering refers to the local deformation of a metal due to the entrapment of hydrogen molecules in the metal voids. Initially, hydrogen atoms diffuse into metal and react with each other to form a hydrogen molecule.
4. What is meant by hydrogen embrittlement?
a) Entrapment of hydrogen molecules in the metal voids
b) Formation of brittle metal hydrides
c) Entrapment of metal hydrides in the metal voids
d) Entrapment of hydrogen molecules and metal hydrides in the metal voids
Answer: b
Explanation: Hydrogen embrittlement refers to the loss of ductility and strength of a metal due to the formation of brittle metal hydrides. Strong hydride forming metals such as titanium, results in brittle fracture.
5. Which of the following types of hydrogen damage processes are high-temperature processes?
a) Hydrogen blistering and hydrogen attack
b) Hydrogen attack and Decarburization
c) Decarburization and hydrogen embrittlement
d) Hydrogen attack only
Answer: b
Explanation: Hydrogen attack and decarburization are high-temperature processes. Decarburization refers to the removal of carbon from metal, is often produced by moist hydrogen at high temperatures. Hydrogen attack refers to the interaction of hydrogen and metal at high temperatures.
6. Which of the following industries has a major concern on hydrogen blistering?
a) Petroleum industry
b) Chemical manufacturing industries
c) Oil and natural gas refineries
d) Oil and natural gas refineries, petroleum and chemical manufacturing industries
Answer: d
Explanation: Hydrogen blistering refers to the local deformation of a metal due to the entrapment of hydrogen molecules in the metal voids.
Industries that have a major concern on hydrogen blistering are:
Petroleum industry
Chemical manufacturing industries
Oil and natural gas refineries
Welding workshops.
7. Which of the following type of compounds act as an inhibitor for hydrogen-ion reduction?
a) Sulfide ions
b) Phosphorous compounds
c) Arsenic compounds
d) Sulfide ions, phosphorous and arsenic compounds
Answer: d
Explanation: Hydrogen atoms diffuse into steel and other metals, which results in hydrogen blistering and hydrogen embrittlement. These inhibitors such as sulfide ions , phosphorous, and arsenic compounds reduce the rate of hydrogen-ion reduction.
8. Which of the following type of corrosion is depicted in the given figure?
a) Filiform corrosion
b) Hydrogen embrittlement
c) Hydrogen blistering
d) Uniform corrosion
Answer: c
Explanation: Hydrogen blistering is depicted in the given figure. It refers to the local deformation of metal with the entrapment of hydrogen molecules in the metal voids.
9. Which of the following type of corrosion is depicted in the given figure?
a) Hydrogen blistering
b) Hydrogen embrittlement
c) Filiform corrosion
d) Selective leaching
Answer: b
Explanation: Hydrogen embrittlement is depicted in the given figure. It refers to the loss of ductility and tensile strength of metal due to the formation of the respective metal hydride.
10. Which of the following metal is highly susceptible to hydrogen embrittlement?
a) Titanium
b) Nickel
c) Martensitic iron-base alloys
d) Titanium and martensitic iron-base alloys
Answer: d
Explanation: Hydrogen embrittlement refers to the brittle cracking failure of reactive metals due to the formation of metal hydrides. Titanium, ferritic, and martensitic iron-base alloys are susceptible to hydrogen embrittlement.
11. Which of the following type of corrosion in which corrosion occurs due to the presence of hydrogen sulfide?
a) Hydrogen embrittlement
b) Hydrogen blistering
c) Sulfide stress corrosion
d) Erosion corrosion
Answer: c
Explanation: Sulfide stress cracking occurs in the presence of water and hydrogen sulfide. It is highly concerned with petroleum industries and oil refining industries.
12. Which of the preventions is/are the preventions of hydrogen blistering?
a) Use of clean steel instead of rimmed steel
b) Applying metallic, inorganic and organic coatings
c) Use of substituting alloys such as nickel-based alloys
d) Use of clean steel instead of rimmed steel, applying metallic, inorganic and organic coatings and use of nickel-based alloys
Answer: d
Explanation: Preventions of hydrogen blistering are:
Use of clean steel instead of rimmed steel
Applying metallic, inorganic and organic coatings
Use of substituting alloys such as nickel-based alloys
Removing poisons such as sulfides, arsenic compounds, cyanides, and phosphorus ions.
13. Which of the following is/are the preventions of hydrogen embrittlement?
a) Baking of steels at low temperatures
b) Alloying with nickel or molybdenum reduces susceptibility
c) Practicing proper welding with low hydrogen welding rods
d) Baking of steels at low temperatures, alloying with nickel or molybdenum reduces susceptibility and practicing proper welding with low hydrogen welding rods.
Answer: d
Explanation: Preventions of hydrogen embrittlement are:
Baking of steels at low temperatures
Alloying with nickel and molybdenum reduces susceptibility
Practicing proper welding with low hydrogen welding rods.
This set of Corrosion Engineering Multiple Choice Questions & Answers focuses on “Exposure Techniques and its Factors – 1”.
1. Well-planned and executed tests usually result in reproducibility and reliability.
a) True
b) False
Answer: a
Explanation: Well-planned and executed corrosion tests result in reproducibility and reliability. The test needs to duplicate the actual plant service conditions as closely as possible.
2. Which of the following is/are the types of corrosion testing?
a) Laboratory testing
b) Pilot-plant testing
c) Field testing
d) Laboratory, pilot-plant and field testing
Answer: d
Explanation: Types of corrosion testings:
Laboratory testing
Pilot-plant testing
Actual plant service test
Field test.
3. Which of the following type of corrosion tests are usually best and more desirable?
a) Laboratory testing
b) Pilot-plant testing
c) Both laboratory and pilot-plant testing
d) Neither laboratory nor pilot-plant testing
Answer: b
Explanation: Pilot-plant tests are usually best and more desirable. It duplicates the intended large-scale operation environment by using the same raw materials, concentrations, temperature, and volume of corrosive solution to the area of metal exposed.
4. Which of the following is/are the purpose of corrosion testings?
a) Evaluation and selection of materials for a specific environment
b) To know the effect on the corrosion of metals by addition of inhibitors
c) To study the mechanism of corrosion
d) Evaluation and selection of materials for a specific environment, to know the effect on the corrosion of metals by addition of inhibitors and to study the mechanism of corrosion
Answer: d
Explanation: Purpose of corrosion testing are:
Evaluation and selection of materials for a specific environment
To know the effect of corrosion on metals by the addition of inhibitors
To study the mechanism of corrosion
To control the corrosion resistance of metal or corrosiveness of the environment.
5. What is the purpose of the salt-spray test?
a) To evaluate painted surfaces
b) To evaluate electroplated parts
c) To evaluate painted surfaces and electroplated parts
d) Neither to evaluate painted surfaces nor to evaluate electroplated parts
Answer: c
Explanation: Salt-spray test is a type of corrosion testing in which specimen is exposed to seawater or salt water in a box. It is usually used to evaluate painted surfaces and electroplated parts.
6. Which of the following statement is/are true regarding the Huey test?
a) Boiling 65% nitric acid is used as a corrosive solution
b) Used to evaluate the heat treatment of steels
c) Used to evaluate the heat treatment of stainless steels
d) Boiling 65% nitric acid is used as a corrosive solution and used to evaluate the heat treatment of stainless steels
Answer: d
Explanation: The Huey test is used to check the heat treatment of stainless steels. It uses boiling 65% nitric acid as a corrosive solution. Stainless steel is an alloy of iron, carbon, chromium, and nickel.
7. Which of the following specifications of the specimen is must increase the reliability of a corrosion test?
a) Chemical composition
b) Fabrication history
c) Metallurgical history
d) Chemical composition, fabrication history, and metallurgical history
Answer: d
Explanation: Exact chemical composition, fabrication history, and metallurgical history of a specimen are must increase the reliability of a corrosion test. Specimen with 1/16 to ¼ inch thick, 1 inch wide, and 2-inch-long are commonly employed for laboratory testing.
8. A standard surface condition is also desirable and necessary to facilitate comparison with other results.
a) True
b) False
Answer: a
Explanation: A surface finish of a specimen is one of the factors of corrosion. It is necessary to have a standard surface condition to facilitate comparison with another result. A common and widely used surface finish is produced by polishing with 120 numbered abrasive cloth.
9. Which of the following methods is/are used for the surface preparation of a specimen?
a) Polishing belts
b) Emery papers
c) Electrolytic polishing
d) Polishing belts, emery papers, and electrolytic polishing
Answer: d
Explanation: The surface finish of the specimen is one of the factors of corrosion. Surface preparation of a specimen can be done by using polishing belts, emery papers, and electrolytic polishing.
10. Which of the following type of corrosion testing is depicted in the given figure?
a) Field testing
b) Pilot-plant testing
c) Laboratory testing
d) Both field testing and pilot-plant testing
Answer: c
Explanation: Laboratory testing is one of the classifications of corrosion tastings. It serves as a most useful function as screening tests to determine which materials warrant further investigation.
11. Which of the following is the formula to calculate the minimum testing time for a corrosion test?
a) 2000/milli meters per year
b) 2000/mils per year
c) 1000/millimeters per year
d) 1000/mils per year
Answer: b
Explanation: A rough rule for checking results concerning minimum test time is 2000/mils per year. Here mils are also known as milli inches i.e. 1/1000th of an inch.
2000/mils per year = hours
12. Which of the following metals is/are subjected to increased attack in the presence of oxygen?
a) Aluminum and its alloys
b) Copper and its alloys
c) Cast iron and steel
d) Copper and its alloys, cast iron and steels
Answer: d
Explanation: Dissolved oxygen will be reduced cathodically into hydroxide ions in many of the corrosion systems and it increases the dissolution of metal anodically. Metals such as copper and its alloys, cast iron and steels are subjected to increase attack in the presence of oxygen.
13. Which of the following metals are resistant to dissolved oxygen?
a) Stainless steels
b) Aluminum and its alloys
c) Stainless steels, aluminum, and its alloys
d) Cooper and its alloys
Answer: c
Explanation: Metals such as aluminum and its alloys, stainless steel is highly resistant to oxygenated corrosive solutions. These metals result in the formation of respective stable oxides.
14. What is liquid-line corrosion?
a) Corrosion on the external surface of a fully-loaded water tank
b) Corrosion at the interface of liquid and gases in a pipeline or tank
c) Preferential corrosion of rivets over sheets in a storage container
d) Corrosion on the external surface of a half-loaded storage tank
Answer: b
Explanation: Liquid-line corrosion is a special type of corrosion that occurs at the interface of liquid and gas in a pipeline or tank. It occurs due to the availability of water vapor and oxygen at the interface along with impurities.
15. Which of the following is/are the cleaning methods after the exposure of specimen?
a) Sandblasting
b) Rubber-stopper
c) Use of chemical and solvents
d) Sandblasting, rubber-stopper and use of chemical and solvents
Answer: d
Explanation: Cleaning methods after the exposure of specimen:
Mechanical methods such as scraping, brushing, sandblasting and the rubber stopper
Chemical methods in which chemical solutions and solvents are used for removal
Electrolytic methods in which specimen is made cathode under an impressed current.
This set of Corrosion Engineering Multiple Choice Questions & Answers focuses on “Testing – Exposure Techniques and its Factors – 2”.
1. The Corrodibility of the metal in a corrosion test may decrease or increase as a function of time.
a) True
b) False
Answer: a
Explanation: Corrodibility of the metal is defined as the capability of being corroded. It may decrease or increase during the corrosion test as a function of time. It increases as it owing to the formation of a protective layer or it decreases as it owing removal of the more resistant surface layer.
2. Which of the following is/are the factors that affect corrosion testing?
a) Temperature
b) Dissolved oxygen
c) Nature of metal
d) Temperature, dissolved oxygen, and nature of metal
Answer: d
Explanation: The factors that affect corrosion testing are:
i. Temperature
ii. Dissolved oxygen
iii. Nature of metal
iv. The concentration of the corrosive solution
v. Specifications of the specimen .
3. Which of the following metals in which corrosion decreases with an increase in temperature in oxygenated corrosive solutions?
a) Copper and its alloys
b) Steels
c) Cast irons
d) Aluminum and its alloys
Answer: a
Explanation: Temperature is one of the important factors of corrosion. In many cases, an increase in temperature increases the corrosion rate of metals. Whereas it decreases in copper alloys due to the removal of dissolved oxygen.
4. Which of the following standard expression is used to measure the corrosion rate of a metal?
a) Mils per year = W/DAT
b) Mils per year = 534W/DAT
c) Milligrams decimeter per day = 534W/DAT
d) Milligrams decimeter per day = W/DAT
Answer: b
Explanation: Standard expression to measure the corrosion rate in mils per year = 534W/DAT.
Where D is the density of metal, W is weight loss in milligrams, A is the area of exposure in sq. inches, T is time in hours.
5. Which of the following units are used in terms of penetration of pits on a metal?
a) Milligram sq. decimeter per day
b) Mils per year
c) Both MDD and MPY
d) Neither MDD nor MPY
Answer: b
Explanation: Mils per year is commonly used corrosion rate expression as it measures corrosion rate in terms of depth of penetration of pit. Whereas milligram sq. decimeter per day measures the corrosion rate in terms of weight loss of metal.
6. Which of the following expression is used for electrochemical techniques to determine the corrosion penetration rate?
a) Corrosion penetration rate = K
b) Corrosion penetration rate = K
c) Corrosion penetration rate =
d) Corrosion penetration rate =
Answer: b
Explanation: The corrosion rate expression that is used for electrochemical techniques to determine corrosion penetration rate is K where a is the atomic weight of the metal, i is current density , n is the number of electrons lost, D is the density of metal, K is constant depends on the penetration rate desired.
7. Calculate the corrosion penetration rate of iron that corroding at an electrochemical corrosion rate of 1 microampere/sq. centimeters?
a) 0.212 mpy
b) 0.11 mpy
c) 0.46 mpy
d) 0.64 mpy
Answer: c
Explanation: Corrosion penetration rate = K
a = atomic weight of iron = 55.8 g
i = current density = 1 micrometer/sq. Centimeters
n = valency change = 2
D = density of iron = 7.86 g/cm 3
K = 0.129 for steel
Corrosion penetration rate = 0.129 * [ / ] = 0.46 mpy.
8. Which of the following is/are the corrosion testing’s for stainless steels?
a) Warren test
b) Streicher test
c) Huey test
d) Warren test, Streicher test and huey test
Answer: d
Explanation: Warren test, Streicher test and huey test are the corrosion testing’s for stainless steel. The primary function of these testing’s is to find out the sensitized stainless-steel metal specimens.
9. Which of the following method is the best approach to report the results of the pitting corrosion test?
a) Reporting the number of pits per unit area
b) Reporting maximum depth of a pit
c) Reporting average depth of pits
d) Reporting weight loss of a metal
Answer: b
Explanation: Pitting corrosion is one of the types of corrosion in which perforated metal is formed due to the formation of holes on the metal surface. The best way to report the corrosion testing of pitting is to report the maximum depth of a pit.
10. Which of the following factors are considered to evaluate the paint test?
a) Appearance of coating
b) Presence and extent of corrosion
c) Under film corrosion
d) The appearance of coating, presence, and extent of corrosion and under film corrosion
Answer: d
Explanation: The factors that are considered to evaluate the paint test are:
i. Appearance of coating
ii. Presence and extent of corrosion
iii. Under film corrosion.
This set of Corrosion Engineering Multiple Choice Questions & Answers focuses on “Corrosion of Plastics and Elastomers”.
1. The polymer is a large and heavy molecular chain formed from the interaction of many monomeric units.
a) True
b) False
Answer: a
Explanation: Polymers are the large and heavy molecular chains formed from the interaction of many monomeric units. It includes plastics, elastomers, and materials like polystyrene, etc.
2. Which of the following is/are characteristics of plastics?
a) High stiffness and strength
b) Less thermal and electrical conductivity
c) High corrosive resistance
d) High stiffness and strength, less thermal and electrical conductivity and high corrosive resistant
Answer: d
Explanation: Plastics are one of the classifications of polymers. It has high stiffness and strength, less thermal and electrical conductivity, and high corrosive resistance.
3. Which of the following statement is/are correct regarding elastomers?
a) It has high elastic properties
b) It has weak intermolecular forces of attraction between molecules
c) Rubber is a good example of an elastomer
d) Elastomers have high elastic properties, weak intermolecular forces of attraction and rubber is a good example of an elastomer
Answer: d
Explanation: Elastomers are the part of polymers which have high viscous and weak intermolecular forces of attraction between molecules. It has high elastic properties such as high resilience, elastic deformation. Rubber is a good example of an elastomer.
4. The corrosion mechanism of polymeric and metallic materials are the same in all corrosive environments.
a) True
b) False
Answer: b
Explanation: Polymeric materials corrode differently rather than processes associated with metallic corrosion. Metallic corrosion results in the electrochemical reactions with the dissolution of metal into metal ions. Whereas polymers result in physicochemical processes.
5. Which of the following is/are the physicochemical processes that occur in polymers?
a) Swelling
b) Dissolution
c) Bond rupture
d) Swelling, dissolution and bond rupture
Answer: d
Explanation: The physicochemical processes that occur in polymers due to the corrosive environment are:
Swelling
Dissolution
Bond rupture.
6. Which of the following is/are the causes for the bond rupturing in polymers?
a) Chemical reaction
b) Heat
c) Radiation
d) Chemical reaction, heat, and radiation
Answer: d
Explanation: Causes for the bond rupturing in polymers are:
Chemical reactions such as oxidation, reduction, and dehydrogenation, etc.
Heat
Radiation by sunlight.
7. Which of the following is/are the effects of polymeric corrosion?
a) Alteration of mechanical properties
b) Cracks formation due to internal stress
c) Loss of appearance
d) Alteration of mechanical properties cracks formation due to internal stress and loss of appearance
Answer: d
Explanation: Effects of polymeric corrosion:
Alteration in physical, chemical and mechanical properties
Cracks initiation and formation due to internal stress
Loss of appearance.
8. Which of the following is depicted in the given figure?
a) Metallic dissolution
b) Polymer-solvent interaction
c) Mechanism of polymeric degradation
d) Uniform corrosion of metals
Answer: b
Explanation: The given figure describes various layers formed by polymer-solvent interaction. These layers are solvent, liquid layer, Gel layer, Solid swollen layer, Infiltration layer, and polymer.
9. Which of the following corrosive environments that mostly results in polymeric dissolution?
a) Strongly oxidizing environments
b) Strong acids
c) Strong alkalis
d) Strong oxidizing environments, acids, and alkalis
Answer: d
Explanation: Corrosive environments that mostly results in polymeric dissolution are:
Strong oxidizing environments
Strong acids
Strong alkalis
Water-miscible solvents
Strong solvents.
10. What is Nelson’s method regarding the presentation of corrosion data?
a) A rapid and ready conversion table for various corrosion rate units
b) Schematic arrangement of corrosion data with the change in temperature and concentration
c) Formula oriented method to find corrosion rate
d) A specific corrosion test regarding galvanic corrosion of stainless steel
Answer: b
Explanation: Nelson’s method is a method of summarizing data of corrosion in which the corrosion rate of particular metal is reported with a change in temperature and concentration of the corrosive solution.
11. What is meant by nomography for corrosion rates?
a) Formula oriented method to find corrosion rate
b) A rapid and ready conversion table for various corrosion rate units
c) Schematic arrangement of corrosion data with the change in temperature and concentration
d) A specific corrosion rate measurement method
Answer: b
Explanation: Nomography for corrosion rate is a table in which it readily converts one corrosion rate unit into another corrosion another unit. Units of corrosion rate are namely mils per year , milligram sq. Decimeter per day .
This set of Corrosion Engineering Multiple Choice Questions & Answers focuses on “Materials – Metals and Alloys – 1”.
1. Which of the following properties of metal is often required to consider by corrosion engineer?
a) Physical properties
b) Mechanical properties
c) Chemical properties
d) Physical, mechanical and chemical properties
Answer: d
Explanation: Properties of a metal that is often required to consider by corrosion engineers are:
Physical properties such as density, modulus of elasticity
Mechanical properties such as strength, hardness
Chemical properties such as corrosion resistance, reactivity.
2. Which of the following is not a mechanical property of a metal?
a) Impact strength
b) Creep strength
c) Modulus of elasticity
d) Stress-rupture
Answer: c
Explanation: At a certain point, modulus of elasticity is considered as the physical property of a metal. Because it is an inherent property that cannot be changed by heat treatment or cold working.
3. Which of the following is/are the types of cast irons?
a) Gray cast iron
b) Malleable cast iron
c) Nodular cast iron
d) Gray cast iron, malleable cast iron, and nodular cast iron
Answer: d
Explanation: Cast iron is a generic term that applies to the high carbon-iron alloys containing silicon. Types of cast irons are gray cast iron, white cast iron, malleable cast iron, and nodular cast iron.
4. What is the composition of high-silicon cast iron named Durichlor that has the highest corrosion resistance among cast irons?
a) 14% silicon, 0.95% carbon and 3% molybdenum
b) 10% silicon, 1% carbon and 3% molybdenum
c) 14% silicon and 0.95% carbon
d) 10% silicon and 1% carbon
Answer: a
Explanation: The composition of Durichlor is 14% silicon, 0.95% carbon, and 3% molybdenum. It is a high-silicon cast iron that has the highest corrosion resistance among cast irons.
5. The excellent corrosion resistance of high-silicon irons is due to the formation of a passive SiO 2 surface layer.
a) True
b) False
Answer: a
Explanation: High-silicon cast iron is the type of alloy cast Irons that are formed with high silicon content . The excellent corrosion resistance of these alloys is due to the formation of a passive SiO 2 layer.
6. Which of the following metal is/are regarded as pure iron commercially?
a) Ingot iron
b) Armco iron
c) Wrought iron
d) Ingot and Armco iron
Answer: d
Explanation: Ingot and Armco iron are regarded as pure irons commercially. These are relatively weak and not used where strength is a major requirement. Whereas wrought iron is a mechanical mixture of slag and low-carbon steel.
7. Which of the following are the parameters of the iron-carbon diagram on the x and y-axis respectively?
a) Carbon percentage and Iron percentage
b) Carbon percentage and temperature
c) Temperature and carbon percentage
d) Iron percentage and temperature
Answer: b
Explanation: The iron-carbon phase diagram is an equilibrium phase diagram formed with carbon percentage and temperature parameters on the x and y-axis respectively. It consists of various phases such as alpha iron, austenite phase, delta iron, and its combinations.
8. Which of the following is/are the classification types of stainless steel?
a) Martensitic stainless steels
b) Ferritic stainless steels
c) Austenitic stainless steels
d) Martensitic, ferritic and austenitic stainless steels
Answer: d
Explanation: Stainless steel is a generic term that applies to iron-carbon-chromium and nickel alloy system. Types of stainless steels are Martensitic stainless steels, ferritic stainless steels, austenitic stainless steels, and precipitation-hardened steels.
9. Which of the following statements are correct regarding the austenite phase in an iron-carbon phase diagram?
a) It is non-magnetic in nature
b) The maximum percentage of carbon is 2.1%
c) It has a face-centered cubic structure
d) The austenitic phase has a face-centered cubic structure with a 2.1% maximum percent carbon and non-magnetic in nature.
Answer: d
Explanation: Austenite is one of the phases in the iron-carbon phase diagram. It has a face-centered cubic structure with 2.1% maximum percent carbon and it is non-magnetic in nature.
10. Which of the following properties of aluminum contributing to its widespread applications?
a) High corrosive resistance
b) Good strength-weight ratio
c) Nontoxic corrosion products
d) High corrosive resistance, good strength-weight ratio, and nontoxic corrosion products
Answer: d
Explanation: The properties of aluminum that contribute to its widespread applications are high corrosion resistance, good strength-weight ratio, nontoxic corrosion products, appearance, and electrical and thermal conductivity.
11. Which of the following metal is utilized in trucks, automobile engines, aircraft, and missiles?
a) Stainless steel
b) Carbon steels
c) Magnesium
d) Cast irons
Answer: c
Explanation: Magnesium is one of the lightest commercial metal with specific gravity 1.74. It is utilized in trucks, automobile engines, aircraft, and missiles. Whereas metals such as stainless steel, carbon steels, and cast irons are regarded as heavy metals.
12. Which of the following corrosion products of lead serve as protective films?
a) Lead sulfates
b) Lead oxides
c) Lead phosphates
d) Sulfates, oxides, and phosphates of lead
Answer: d
Explanation: Lead and its alloys are usually used piping, radiation shield, and storage batteries. It is resistant to corrosion in sulfuric acid, chromic acid, and phosphoric acid. Sulfates, oxides, and phosphates of lead are the corrosion products of lead that act as protective films.
13. Which of the following alloying element of stainless steel that attributes a large increase in stress-corrosion resistance?
a) Nickel
b) Chromium
c) Carbon
d) Nickel and chromium
Answer: a
Explanation: Stainless steel is a generic term that attributes to the alloy system of iron-carbon-chromium and nickel. Addition of nickel as alloying element up to 10% attributes in a rapid and large increase in stress-corrosion resistance of stainless steel.
14. Which of the following metal/alloy has the highest stress-corrosion resistance?
a) Aluminum
b) Inconel
c) Stainless steel
d) Titanium
Answer: b
Explanation: Typical composition of an Inconel is chromium 20-23%, iron 5%, molybdenum 8-10% and nickel around 60-65%. Inconel has the highest stress-corrosion resistance whereas aluminum, stainless steel, and titanium are prone to stress corrosion cracking.
15. Which of the following metals will have the same crystal structure as that of the given figure?
a) Zinc
b) Nickel
c) Titanium
d) Zinc and titanium
Answer: b
Explanation: The given figure depicts a face-centered crystal structure. Nickel is face-centered cubic structure material whereas zinc and titanium are hexagonal closed packed structures.
This set of Corrosion Engineering Question Bank focuses on “Materials – Metals and Alloys – 2”.
1. Which of the following metals will act as sacrificial metals in cathodic production?
a) Tin and zinc
b) Zinc only
c) Magnesium, zinc and magnesium
d) Magnesium and tin
Answer: c
Explanation: Sacrificial metals are the metals that corrode preferentially over the metallic structure that needs to be protected. This cathodic protection works on the principle of the galvanic effect. Tin, zinc, magnesium are the common sacrificial metals used.
2. Which of the following metal is/are corrosion resistant to hydrofluoric acid?
a) Hastelloy C
b) Monel
c) Hastelloy C and Monel
d) Titanium
Answer: c
Explanation: Hastelloy C and Monel are corrosion-resistant metals to hydrofluoric acid. Whereas titanium and most other metals usually corrode in hydrofluoric acid.
3. Which of the following metal plating is used for high-strength steels in aircraft to improve resistance to corrosion fatigue?
a) Cadmium
b) Magnesium
c) Zinc
d) Lead
Answer: a
Explanation: Corrosion fatigue is the simultaneous effect of fatigue and corrosion on a working metal. Cadmium plating is used for high-strength steels in aircraft to improve resistance to corrosion fatigue.
4. Which of the following metals will depend on the oxide layer for their corrosion resistance?
a) Titanium and stainless steels
b) Titanium, stainless steels, and aluminum and its alloys
c) Aluminum and its alloys
d) Aluminum and its alloy and titanium
Answer: b
Explanation: Corrosion resistance of the metal is the ability of a metal to withstand the effect of a corrosive environment. Titanium, stainless steel, and aluminum and its alloys will resist the corrosive environment with the formation of their oxide layer.
5. Which of the following metals has a Hexagonal closed packed structure?
a) Cadmium
b) Magnesium
c) Zirconium
d) Cadmium, magnesium, and zirconium
Answer: d
Explanation: Crystal structures are classified into 14 different types known as Bravais lattice based on the shape of the unit cell and position of atoms in it. Cadmium, magnesium, zirconium, titanium, zinc, and beryllium are examples of hexagonal closed packed structures.
6. Which of the following characteristics of titanium that account for much of its application in corrosive services?
a) Resistance to seawater and other chloride salt solutions
b) Resistance to hypochlorite’s and wet chlorine
c) Resistance to fuming nitric acid
d) Resistance to seawater, chloride salt solutions, hypochlorite’s, wet chlorine and fuming nitric acid
Answer: d
Explanation: Titanium is an excellent corrosion-resistant metal in many corrosive environments. The characteristics of titanium that account for much of its application in corrosion services are its resistance to seawater, chloride salt solutions, hypochlorite’s, wet chlorine, and fuming nitric acid.
7. Which of the following metals are regarded as refractory metals?
a) Niobium and tungsten
b) Molybdenum only
c) Niobium, molybdenum, and tungsten
d) Tungsten and molybdenum only
Answer: c
Explanation: Refractory metals are characterized by very high melting points with limited corrosion resistance. Tantalum, niobium, molybdenum, tungsten, and zirconium are regarded as refractory metals.
8. Which of the following metals that usually results in a porous and volatile oxide layer?
a) Magnesium
b) Molybdenum
c) Sodium
d) Magnesium, sodium, and molybdenum
Answer: d
Explanation: If the Pilling-bed worth ratio of a particular metal is less than 1 then it results in a porous, volatile, and thin oxide layer. Sodium, molybdenum, and magnesium are examples of this kind.
9. Which of the following metals are regarded as noble metals?
a) Iridium
b) Palladium
c) Ruthenium
d) Iridium, palladium, and ruthenium
Answer: d
Explanation: Noble metals are the metals that are characterized by highly positive potentials relative to the hydrogen electrode along with excellent corrosion resistance. This includes iridium, palladium, ruthenium, rhodium, osmium, gold, silver, and platinum.
10. What is the composition of aqua-regia that corrodes noble metals such as platinum, gold?
a) 3 parts of nitric acid and 1 part of hydrochloric acid
b) 3 parts of hydrochloric acid and 1 part of nitric acid
c) 1 part of hydrofluoric acid and 3 part of hydrochloric acid
d) 3 parts of hydrofluoric acid and 1 part of hydrochloric acid
Answer: b
Explanation: The composition of aqua regia is 3 parts of hydrochloric acid and 1 part of nitric acid. It corrodes/dissolves noble metals such as gold, platinum, and palladium.
11. What is the abbreviation of BMG regarding the type of materials?
a) Bulk metallic groups
b) Bulk metallic glasses
c) Body metallic glasses
d) Body metallic groups
Answer: b
Explanation: Bulk metallic glasses are the non-crystalline alloys that are formed with low critical cooling rates. These bulk metallic glasses exhibit useful engineering properties such as high mechanical strength and high corrosion resistance.
12. Metallic composites consist of a metallic matrix strengthened by metallic or nonmetallic fibers, filaments or whiskers.
a) True
b) False
Answer: a
Explanation: Composites are the type of materials that are formed by the combination of two or more materials. And metallic composites consist of a metallic matrix strengthened by metallic or nonmetallic fibers or whiskers. This includes boron, graphite, glass, and metal.
13. Which of the following factors that affect the corrosion of composites?
a) The corrosive specificity of an environment
b) Galvanic effect
c) Corrosive specificity of an environment and galvanic effect
d) Neither the corrosive specificity of an environment nor the galvanic effect
Answer: c
Explanation: The corrosion specificity of an environment and galvanic effect are the factors that affect the corrosion of composites. Thus, if the matrix and filament of a composite are close together in the galvanic series. galvanic effects are negligible.
14. Which of the following is the monomer of natural rubber?
a) Isoprene
b) Neoprene
c) Vinyl chloride
d) Styrene
Answer: a
Explanation: Natural rubber is a long-chain molecule of isoprene which is chemically known as polyisoprene. It is obtained from trees as liquid latex. The properties of natural rubber can be improved by the process known as vulcanization of rubber.
Answer: c
Explanation: The packing fraction of a given crystal structure is defined as the ratio of the volume of atoms in the unit cell to the volume of the unit cell. Given crystal structure is body-centered cubic and its packing fraction is 0.68.
This set of Corrosion Engineering Multiple Choice Questions & Answers focuses on “Materials – Thermoplastics”.
1. Which of the following is/are the classification of plastics based on the thermal behavior?
a) Thermoplastics
b) Thermosetting
c) Neither thermoplastics nor thermosetting
d) Thermoplastics and thermosetting
Answer: d
Explanation: Plastics can be categorized based on various parameters such as monomer units, temperature behavior, and structure. Thermoplastics and Thermosetters are the two types of plastics based on thermal behavior.
2. What is meant by thermoplastic?
a) It softens on heating and returns to original hardness on cooling
b) It hardens on heating and returns to original hardness on cooling
c) It hardens on heating and retains hardness on cooling
d) It softens on heating and retains hardness on cooling
Answer: a
Explanation: Thermoplastics is one of the type of plastics which softens on heating and returns to original hardness on cooling. Fluorocarbons, polyether, and nickel are examples of thermoplastics.
3. Which of the following thermoplastic is corrosion-resistant to all environments up to 550°F?
a) Polyvinyl chloride
b) Polystyrene
c) Teflon
d) Polyethylene
Answer: c
Explanation: Teflon is one of the fluorocarbons which is regarded as noble metals of plastics. It is corrosion-resistant to practically all environments up to 550°F. The monomer of Teflon is denoted as CF 2 =CF 2 .
4. Which of the following is the chemical name of nylon ?
a) Polyethylene terephthalate
b) Hexamethylene adipamide
c) Polytetrafluoroethylene
d) Polyvinyl fluoride
Answer: b
Explanation: The chemical name of nylon is hexamethylene adipamide. It is derived from the monomers of nylon that are hexamethylenediamine and adipic acid.
5. Which of the following thermoplastics is used for making eye lenses?
a) Polytetrafluoroethylene
b) Polyethylene terephthalate
c) Polymethyl methacrylate
d) Polyvinyl chloride
Answer: c
Explanation: Polymethyl methacrylate is the polymer of many methyl methacrylate monomeric units. It is used for making eye lenses as it is transparent to light. It is usually denoted as PMMA.
6. Which of the following is/are the monomers of nylon ?
a) Hexamethylenediamine
b) Adipic acid
c) Both Hexamethylenediamine and adipic acid
d) Neither Hexamethylenediamine nor adipic acid
Answer: c
Explanation: Hexamethylenediamine and adipic acid are the two monomers of nylon . The chemical formula of hexamethylenediamine and adipic acid is NH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -NH 2 and HOOC-CH 2 -CH 2 -CH 2 -COOH respectively.
7. Which of the following is/are the examples of thermoplastics?
a) Polypropylene
b) Polystyrene
c) Polyvinyl chloride
d) Polypropylene, polystyrene and polyvinyl chloride
Answer: d
Explanation: Thermoplastics are the type of plastics that soften on heating and return to their original hardness when cooled. Polypropylene, polystyrene, polyethylene, fluorocarbons, and polyvinyl chloride are examples of thermoplastics.
8. Which of the following thermoplastic monomer is depicted in the given figure?
a) Polystyrene
b) Teflon
c) Polyvinyl chloride
d) Polyurethane
Answer: a
Explanation: Styrene is depicted in the given figure and it is the monomer of polystyrene. It is an amorphous, colorless, rigid, and hard plastics. The monomer of polyvinyl chloride and Teflon is CH 2 =CH-Cl and CF 2 =CF 2 respectively.
9. Which of the following is the monomer of Polyvinyl chloride ?
a) CF 2 =CF 2
b) CH 2 =CH-Cl
c) COOH-CH 2 -CH 2 -CH 2 –CH 2 COOH
d) C 6 H 5 -CH=CH 2
Answer: b
Explanation: Vinyl chloride (CH 2 =CH-Cl) is the monomeric unit of polyvinyl chloride. It is used for piping and cable insulation extensively. CF 2 =CF 2 , COOH-CH 2 -CH 2 -CH 2 –CH 2 COOH and C 6 H 5 -CH=CH 2 are the monomers of Teflon, nylon, and polystyrene respectively.
10. Degradation of plastics is due to swelling, loss of mechanical properties, softening, hardening, and spalling.
a) True
b) False
Answer: a
Explanation: Corrosion of plastics is not the same as that of metals. Corrosion of metals results in the dissolution of metal ions whereas corrosion or degradation of plastics is due to swelling, loss of mechanical properties, softening, hardening, and spalling.
This set of Corrosion Engineering Multiple Choice Questions & Answers focuses on “Materials – Thermosetters”.
1. What is meant by thermosetting plastic?
a) It softens on heating and returns to original hardness on cooling
b) It hardens on heating and retains hardness on cooling
c) It hardens on heating and returns to original hardness on cooling
d) It softens on heating and retains hardness on cooling
Answer: b
Explanation: Plastics are readily divided into two types based on their thermal behavior. One is thermoplastic and another one is thermosetting. Thermosetting polymers are the polymers that harden on heating and retains hardness on cooling.
2. Which of the following is/are the example of thermosetting polymers?
a) Epoxies
b) Polyesters
c) Phenolics
d) Epoxies, polyesters, and phenolics
Answer: d
Explanation: Thermosetting polymers is one of the classifications of polymers based on the thermal behavior of polymers. Epoxies, polyesters, and phenolics are examples of thermosetting polymers.
3. Which of the following is/are the raw materials of Bakelite?
a) Phenol
b) Formaldehyde
c) Both phenol and formaldehyde
d) Neither phenol nor formaldehyde
Answer: c
Explanation: Bakelite is one of the most widely used thermosetting plastics for various domestic and industrial applications. Phenol or carbolic acid and formaldehyde are the raw materials of Bakelite.
4. Which of the following polyester is used in the space mirror satellite?
a) Mylar
b) Dacron
c) Vibrin
d) Dypol
Answer: a
Explanation: Thermosetting polymers such as Mylar, Dacron, Vibrin, and Dypol are categorize under polyester. The satellite was made of thin, reflective Mylar film.
5. Silicones are used for molding compounds, laminating resins, and insulation for electric motors and electronic equipment.
a) True
b) False
Answer: a
Explanation: Silicones are used for the molding compounds, laminating resins, and insulating for electric motors and electronic equipment because of its outstanding heat resistance. It can be demonstrated by Si–O–Si bond with alkyl groups on either side of the silicon atom.
6. What is the chemical name of the compound that is depicted in the given figure?
a) Formaldehyde
b) Bakelite
c) Urea
d) Vinyl chloride
Answer: c
Explanation: The compound that is depicted in the given figure is urea. It is one of the monomers of bauxite and beetle. It combines with formaldehyde to form plastics that used for the applications of kitchen dishware and utensils.
7. What is the abbreviation of FRP regarding reinforced plastics?
a) Filtrate-reinforced plastic
b) Fiber-reinforced plastic
c) Filter-reinforced plastic
d) Fume-reinforced polymer
Answer: b
Explanation: FRP can be abbreviated as Fiber-reinforced plastic regarding reinforced plastics. Carbon fibers, alumina fibers, an aramid fiber can be reinforced into plastics for better strength and corrosion resistance.
8. Which of the following thermosetting plastics that comes under phenolics?
a) Bakelite
b) Durez
c) Resinox
d) Bakelite, Durez, and Resinox
Answer: d
Explanation: Phenolics materials such as Bakelite, Durez, and Resinox are made up of phenol and formaldehyde. It uses for various applications such as electrical sockets, telephones, valves, and coatings.
9. Which of the following category that materials such as Epon, Durcon, and Araldite belong to?
a) Epoxies
b) Silicones
c) Phenolics
d) Polyesters
Answer: a
Explanation: Epon, Durcon, and Araldite belong to epoxies. These materials are the best combination of corrosion resistance and mechanical properties. It is mainly used as protective coatings, linings, and adhesives.
10. Which of the following is not a thermosetting plastic?
a) Dacron
b) Bakelite
c) Polystyrene
d) Polyester
Answer: c
Explanation: Thermosetting plastic is a plastic that hardens on heating and retains hardness on cooling. Dacron, Bakelite, and Polyester are examples of thermosetting plastics whereas Polystyrene is the example of thermoplastics.
This set of Corrosion Engineering Problems focuses on “Materials – Other Nonmetallics”.
1. Which of the following compounds that are present in ceramics?
a) Metallic elements
b) Non-metallic elements
c) Both metallic and non-metallic elements
d) Neither metallic nor non-metallic elements
Answer: c
Explanation: Ceramics are the other class of non-metallics. It usually consists of metallic and non-metallic elements. Magnesia, porcelain is the best examples of ceramics.
2. Which of the following is/are the examples of ceramics?
a) Brick
b) Stone
c) Fused silica
d) Brick, stone and fused silica
Answer: d
Explanation: Examples of ceramics are brick, stone, fused silica, stoneware, glass, clay, porcelain, concrete, abrasives, mortars, and high-temperature refractories.
3. Which of the following is/are the advantages of ceramics?
a) Resistance to higher temperatures only
b) Better corrosion resistance and resistance to higher temperatures
c) High abrasion resistance
d) Resistance to high temperatures, better corrosion resistance, and high abrasion resistance
Answer: d
Explanation: Advantages of ceramic materials are:
i. Resistance to higher temperatures
ii. Better corrosion resistance
iii. High abrasion resistance.
4. Which of the following is/are the disadvantages of ceramics?
a) Brittle in nature
b) Less tensile strength
c) Less resistance to thermal shocks
d) Brittle in nature, less tensile strength and less resistance to thermal shocks
Answer: d
Explanation: Disadvantages of ceramic materials are:
i. Brittle in nature
ii. Less tensile strength
iii. Less resistance to thermal shocks.
5. Which of the following is/are the ultra-tough ceramics that could be used in diesel engines?
a) Silicon carbide and zirconia
b) Silicon carbide, alumina, and zirconia
c) Zirconia only
d) Alumina and silicon carbide
Answer: b
Explanation: Much research is ongoing to produce ultra-tough ceramics such as silicon carbide, silicon nitride, alumina, and zirconia. This research aims to reduce the brittleness such that these materials could be used in diesel engines and gas turbines.
6. Acid brick is the material made from fireclay with a silica content about 10% greater than ordinary firebrick.
a) True
b) False
Answer: a
Explanation: Acid brick is the material made from fireclay with a silica content about 10% greater than ordinary firebrick. It is usually used for the construction of the floor of steel tanks that are subjected to acid spillage.
7. Which of the following statements regarding glass is/are correct?
a) It is an amorphous inorganic oxide
b) It composed of pure silica
c) It is mostly transparent in nature
d) It is an amorphous inorganic oxide, composed of pure silica and mostly transparent in nature
Answer: d
Explanation: Glass is an amorphous inorganic solid, mostly silica, cooled to a rigid condition without crystallization. Its transparency is used for equipment such as flowmeters and glass fibers.
8. What is the other name of fused quartz?
a) Vitreous silica
b) Amethyst
c) Citrine
d) Rutilated quartz
Answer: a
Explanation: Vitreous silica is also called fused silica. It has better thermal properties and corrosion resistance at high temperatures than most ceramics. Whereas amethyst, citrine, and rutilated quartz are the types of quartz.
9. Which of the following is/are the characteristics of carbon and graphite?
a) It has good thermal and electrical conductivity
b) Excellent thermal shock resistance
c) It has good thermal and electrical conductivity, excellent thermal shock resistance, weak and brittle as compared with metals
d) Weak and brittle as compared with metals and have excellent thermal shock resistance
Answer: c
Explanation: Carbon and graphite are the unique non-metallics that are good thermal and electrical conductors with excellent thermal shock resistance. They are weak and brittle as compared with metals.
10. Which of the following types of wood are used for corrosion applications?
a) Oak, redwood, and pine
b) Pine only
c) Redwood and oak
d) Redwood only
Answer: a
Explanation: Generally, wood is not a corrosion-resistant material but in particular circumstances, it can be used in the account of being economical. Cypress, pine, oak, and redwood are the types of woods used for corrosion applications.
This set of Corrosion Engineering Multiple Choice Questions & Answers focuses on “Prevention – Material Selection and Design – 1”.
1. The most common method of preventing corrosion is the selection of the proper metal or alloy for a particular corrosive service.
a) True
b) False
Answer: a
Explanation: There is no such single material that can be used in all environment conditions and all temperature ranges. So, it is important to select a proper metal or alloy for a particular corrosive service. It prevents or reduces the corrosion damage of the metallic structure.
2. Which of the following composition range is correct regarding stainless steel?
a) 11.5 to 30% chromium and 10 to 22% nickel
b) 11.5 to 30% chromium and 0 to 22% nickel
c) 0 to 30% chromium and 0 to 22% nickel
d) 0 to 30% chromium and 10 to 22% nickel
Answer: b
Explanation: Stainless steel is the generic name for a series of more than 30 different alloys with composition ranges from 11.5% to 30% chromium and 0 to 22% nickel and other alloying elements.
3. Which of the following types of corrosion in which stainless steels are more susceptible than ordinary steels?
a) Pitting corrosion
b) Stress-corrosion cracking
c) Intergranular corrosion
d) Stress-corrosion cracking, pitting and intergranular corrosion
Answer: d
Explanation: Stainless steels are more susceptible to localized corrosion such as intergranular corrosion, stress-cracking corrosion, and pitting corrosion than ordinary steels. Instability of oxide layer in severe corrosive conditions and sensitizing temperature are the reasons for the susceptibility of stainless steel.
4. Which of the following metal is the best material selection combination for the nitric acid environment?
a) Tin
b) Nickel and its alloys
c) Stainless steels
d) Steel
Answer: c
Explanation: Stainless steels are the best combination of metal for the nitric acid environment. Stainless steels readily form a passive oxide film in nitric acid. This minimizes or reduces the corrosion damage.
5. Which of the following metal is the best material selection combination for the caustic environment?
a) Titanium
b) Nickel and its alloys
c) Steels
d) Aluminum and its alloys
Answer: b
Explanation: Nickel and its alloys are the best combination of metal for the caustic environment. Metals such as titanium and high tensile strength steels are prone to caustic embrittlement.
6. Which of the following metal is the best material selection combination for distilled water?
a) Tin
b) Lead
c) Titanium
d) Nickel
Answer: a
Explanation: Tin is the best combination of metal for distilled water. Tin or tin coatings are almost always chosen as a container or piping material for very pure distilled water.
7. Which of the following metal is/are the correct combination for reducing or non-oxidizing environment?
a) Nickel and its alloys
b) Copper and its alloys
c) Stainless steels
d) Nickel, copper and its alloys
Answer: d
Explanation: Nickel, copper and its alloys are the correct combinations of metals for reducing or non-oxidizing environments. Whereas stainless steels and titanium alloys are stable in an oxidizing environment.
8. Which of the following material is used for handling hydrogen peroxide?
a) Commercially pure metals
b) Alloys
c) Both commercially pure metal and alloys
d) Neither commercially pure metals nor alloys
Answer: a
Explanation: Commercially pure metal such as aluminum is used for handling hydrogen peroxide. Alloys result in the decomposition of hydrogen peroxide due to the catalytic action of alloying elements.
9. Which of the following type of zirconium is used in an atomic-energy application?
a) Induction-melted zirconium
b) Arc-melted zirconium
c) Both arc-melted and induction-melted zirconium
d) Neither arc-melted nor induction melted zirconium
Answer: b
Explanation: Arc-melted zirconium is more corrosion resistant than induction-melted zirconium because of more impurities in the latter. Hence arc-melted zirconium is used in an atomic-energy application.
10. Which of the following is/are the different classes of non-metallics?
a) Ceramics and wood
b) Plastics and ceramics
c) Wood, ceramics, and plastic
d) Ceramics only
Answer: c
Explanation: The five general classes of non-metallics are:
Natural and synthetic rubber
Plastics
Ceramicsi
Carbon and graphite.
Wood.
11. Which of the following type of materials possess excellent corrosion and high-temperature resistance?
a) Metals
b) Plastics
c) Ceramics
d) Both ceramics and metals
Answer: c
Explanation: Ceramics are the class of materials that possess excellent corrosion and high-temperature resistance. But brittleness or less tensile strength is the primary limitation of ceramics.
12. Boiling seawater is less corrosive than that of hot seawater.
a) True
b) False
Answer: a
Explanation: Boiling seawater is less corrosive than that of hot seawater. Because the solubility of oxygen in seawater decreases with an increase in temperature. Reduction of oxygen results in severe metallic dissolution in many oxygenated corrosive solutions.
13. Which of the following belongs to the alteration of the environment to minimize corrosion?
a) Decreasing velocity
b) Removing oxygen and oxidizers
c) Changing concentration
d) Decreasing velocity, removing oxygen and oxidizers and changing the concentration
Answer: d
Explanation: Alteration of the environment is one of the measures to minimize corrosion. Alteration of the environment includes
Changing mediums
Lowering temperature
Decreasing velocity
Removing oxidizers
Changing concentrations.
14. Which of the following is/are the functions of magic devices or water-conditioning gadgets?
a) Prevent scaling
b) Destroy bacteria
c) Reduce water hardness
d) Prevent scaling, destroy bacteria and reduce water hardness
Answer: d
Explanation: Magic device or water-conditioning gadgets are the devices to control water corrosion. Purpose of these gadgets are
Prevent scaling
Destroy bacteria
Reduce water hardness
Reduces corrosion.
15. Which of the following metal combination is/are selected as per given requirement in the figure?
a) Gold – Iron
b) Steel – Stainless
c) Brass – Copper
d) Silver – Zinc
Answer: b
Explanation: The given figure indicates the galvanic metal combination. Hence metal combination should be as close as possible in the galvanic series to minimize the galvanic effect. Hence good metal combination is brass and copper.
This set of Corrosion Engineering Questions and Answers for Entrance exams focuses on “Prevention – Material Selection and Design – 2”.
1. Since corrosion is a penetrating action, it is necessary to make allowances for the reduction in thickness in designing pipes and tanks.
a) True
b) False
Answer: a
Explanation: Since corrosion is a penetrating action, it is necessary to make allowances for the reduction in thickness in designing pipes and tanks to meet the mechanical requirements of the service.
2. What should be the approximate thickness of a wall for better performance if the corrosion rate of that wall is estimated as 1/8 inches in 1 year?
a) 1/2 inches
b) 1/8 inches
c) 1/4 inches
d) 1/16 inches
Answer: c
Explanation: The approximate thickness of a wall should be twice that of the estimated corrosion rate to meet the mechanical requirements such as pressure, weight, and stress. Hence, the thickness of the given wall is 2* = ¼ inches.
3. Which of the following design of vessels is/are preferred regarding corrosion prevention?
a) Sharp-edged vessel only
b) Curve edged vessel only
c) Both sharp and curve edged vessel
d) Neither sharp nor curve edged vessel
Answer: b
Explanation: Sharp edges components result in the formation of crevices whereas has curve edged components result in proper circulation of solution throughout the component and eliminates crevice corrosion.
4. Which of the following is/are the design rules for corrosion prevention?
a) Weld rather than riveting containers
b) Design systems for easy replacement of components that fails rapidly
c) Avoid excessive mechanical stress and stress concentration
d) Weld rather than riveting containers, design systems for easy replacements of components that fail rapidly, and avoid excessive mechanical stress and stress concentration
Answer: d
Explanation: Design rules for corrosion preventions:
Weld rather than the riveting tank and other containers
Design systems for easy replacements of components that fails rapidly
Avoid excessive mechanical stress and stress concentration
Avoid electrical contact between two dissimilar metals.
5. Which of the following is the design rule to reduce erosion-corrosion?
a) Avoid excessive mechanical stress
b) Avoid sharp bend in piping systems
c) Avoid sharp bends in piping systems and provide thicker sections to reduce impingement effects
d) Avoid sharp bends in the piping system and excessive mechanical stress
Answer: c
Explanation: Erosion corrosion can be minimized by avoiding sharp bends in the piping system and provide a thicker section to reduce impingement effects. And the better material selection is also one of the factors to prevent erosion-corrosion.
6. Which of the following is not a design rule for corrosion prevention?
a) Riveting the tanks rather than welding
b) Specify operating and maintenance procedures
c) Tank bottoms should be sloped toward drain holes
d) Avoid electrical contact between dissimilar metals
Answer: a
Explanation: Certain design rules can reduce or minimize the effect of corrosion. That includes welding the tanks rather than riveting. This eliminates the formation of crevices at the riveting area and avoids crevice corrosion.
7. Uneven temperature distribution leads to higher corrosion rates and may result in stress-corrosion cracking failure.
a) True
b) False
Answer: a
Explanation: Stress-corrosion cracking is a combination of stress and a corrosive environment. Uneven temperature distribution leads to internal stress and results in stress-corrosion cracking failure.
8. Which of the following is/are included in the general term avoid heterogeneity?
a) Dissimilar metal contact
b) Different phases such as vapor spaces
c) Uneven heat and stress contribution
d) Dissimilar metal contact, different phases such as vapor spaces, and uneven heat and stress distribution.
Answer: d
Explanation: The design rule to avoid heterogeneity includes dissimilar metal contact, different phases such as vapor spaces, and uneven heat and stress distribution.
This set of Corrosion Engineering Multiple Choice Questions & Answers focuses on “ Corrosion Prevention – Inhibitors”.
1. An inhibitor is a chemical substance that added in small concentrations to an environment, to decrease the corrosion rate.
a) True
b) False
Answer: a
Explanation: An inhibitor is a chemical substance that added in small concentrations to an environment, to decrease the corrosion rate. It is also regarded as a retarding catalyst.
2. Which of the following is/are the types of inhibitors?
a) Adsorption inhibitors
b) Scavengers
c) Vapor-phase inhibitors
d) Adsorption inhibitors, scavengers, and vapor-phase inhibitors
Answer: d
Explanation: Following are the types of inhibitors:
i. Adsorption inhibitors
ii. Scavengers
iii. Vapor-phase inhibitors
iv. Hydrogen-evolution poisons
v. Oxidizers.
3. Which of the following is an example of adsorption-type inhibitors?
a) Arsenic
b) Sodium sulfite
c) Organic amines
d) Chromates
Answer: c
Explanation: Adsorption-type inhibitors are the type of inhibitors that adsorb on the surface of cathode or anode and alter its surface. Organic amines are examples of adsorption-type inhibitors.
4. Which of the following inhibitors are effective in acid solutions?
a) Oxidizers
b) Hydrogen-evolution poisons
c) Vapor-phase inhibitors
d) Oxidizers and hydrogen-evolution poisons
Answer: b
Explanation: Cathodic reduction of hydrogen ions to a hydrogen atom is the main driving force for the metallic dissolution in many acidic environments. It can be reduced or minimized with hydrogen-evolution poisons.
5. Which of the following is/are the examples of Hydrogen-evolution poisons?
a) Arsenic and Antimony
b) Sodium sulfite and hydrazine
c) Chromates and ferric salts
d) Organic amines
Answer: a
Explanation: Hydrogen-evolution poisons are the inhibitors that retard the rate of evolution of hydrogen gas in an acidic environment. Arsenic and Antimony are examples of hydrogen-evolution poisons.
6. Which of the following is/are the examples of scavengers?
a) Arsenic and Antimony
b) Chromates and ferric salts
c) Sodium sulfite and hydrazine
d) Organic amines
Answer: c
Explanation: Scavengers are the type of inhibitors that removes corrosive reagents from the solution. Sodium sulfite and hydrazine are examples of scavengers. 2Na 2 SO 3 +O 2 ==>2Na 2 SO 4 is the scavenging action of sodium sulfite.
7. Oxidizers such as chromates, nitrates, and ferric salts inhibit the corrosion of metal and alloys that demonstrate active-passive transition.
a) False
b) True
Answer: b
Explanation: Oxidizers such as chromates, nitrates, and ferric are one type of inhibitors that inhibit the corrosion of metal and alloys that demonstrate active-passive transition. Active-passive transition metals include iron and stainless steel.
8. Which of the following is/are the characteristics of the vapor phase inhibitor?
a) It has a very high vapor pressure
b) Inhibit the atmospheric corrosion without being contact with the metal surface
c) Effective in closed spaces
d) It has very high vapor pressure, inhibit atmosphere corrosion without being contact with the metal surface and very effective in closed spaces
Answer: d
Explanation: Vapor-phase inhibitors are very similar to organic adsorption-type inhibitors. Characteristics of vapor-phase inhibitors are:
i. It has a very high vapor pressure
ii. Inhibit the atmospheric corrosion without being contact with the metal surface
iii. Effective in closed spaces.
9. Which of the following phenomenon in which the inhibiting effect is sometimes greater than that would be achieved by either of the two or substances alone?
a) Galvanic effect
b) Cathodic protection
c) Synergistic effect
d) Inhibiting effect
Answer: c
Explanation: When two or more inhibiting substances are added to a corrosive system, the inhibiting effect is sometimes greater than that achieved by either of the two or more substances alone. This is called a synergistic effect.
10. Which of the following is/are the limitations of inhibitors?
a) It contaminates the environment
b) Inhibitors are toxic
c) Its efficiency decreases with time and temperature
d) It contaminates the environment, toxic in nature, and its efficiency decreases with time and temperature.
Answer: d
Explanation: Limitations of inhibitors:
i. It contaminates the environment
ii. Inhibitors are toxic in nature
iii. Its efficiency decreases with time and temperature
iv. It should not be used directly or indirectly in the preparation of food.
11. Which of the following inhibitor is used for aluminum in the hydrogen peroxide environment?
a) 2% boron trifluoride
b) Alkali metal nitrates
c) Sodium silicate
d) Benzoic acid
Answer: b
Explanation: Inhibitors are the chemical compounds that decrease the corrosion rate of metal in a specific environment. Alkali metal nitrates are used as inhibitors for the aluminum metal in the hydrogen peroxide environment.
12. Which of the following inhibitor is used for steel in 80% pure sulfuric acid?
a) 2% boron trifluoride
b) Sodium silicate
c) Alkali metal nitrates
d) Benzoic acid
Answer: a
Explanation: Inhibitors are very specific to a particular metal, environment, and the concentration of an environment. 2% boron trifluoride inhibitor is used for steel in 80% pure sulfuric acid.
13. Which of the following inhibitor is used for steel in the water?
a) Sodium silicate
b) Alkali metal nitrates
c) Benzoic acid
d) 2% boron trifluoride
Answer: c
Explanation: Inhibitors are the chemical compounds that decrease the corrosion rate of metal in a specific environment. Benzoic acid is used as an inhibitor for steel in water.
14. Which of the following phenomenon that occurs on metal surface during inhibition?
a) Adsorption only
b) Adsorption and phase layers
c) Phase layers only
d) Neither adsorption nor phase layers
Answer: b
Explanation: Inhibitors are the chemical compounds that decrease the corrosion rate of metal in a specific environment. Inhibition can be caused by both adsorption and phase layers on the metal surface.
This set of Corrosion Engineering Multiple Choice Questions & Answers focuses on “Cathodic and Anodic Protection – 1”.
1. Which of the following is/are the common electrochemical reactions that occur during corrosion?
a) M==>M + +ne
b) 2H + +2e=>H 2
c) O 2 +4H + +4e==>H 2 O
d) M==>M + +ne, 2H + +2e=>H 2 and O 2 +4H + +4e==>H 2 O
Answer: d
Explanation: The common electrochemical reactions that occur during corrosion are:
M==>M + +ne
2H + +2e=>H 2
O 2 +4H + +4e==>H 2 O
2. Cathodic protection is achieved by supplying electrons to the metal structure to be protected.
a) True
b) False
Answer: a
Explanation: Cathodic protection is achieved by supplying electrons to the metal structure to be protected. It can be done by using impressed current in the range of microamperes per unit area of the metallic structure.
3. Which of the following cases in which the metal structure is protected?
a) Current passes from metal to electrolyte
b) Current enters it from the electrolyte
c) Electrical contact with dissimilar metals
d) Connecting the positive terminal of the power supply
Answer: b
Explanation: Metallic structure can be protected when the impressed current is arranged to enter it from the electrolyte. Whereas current passes from metal to electrolyte, electrical contact with dissimilar metals, and connecting the positive terminal of the power supply results in accelerated corrosion.
4. Which of the following is/are the types of cathodic protection?
a) External impressed current supply
b) Sacrificial anode
c) External impressed current supply and sacrificial anode
d) Neither external impressed current supply nor sacrificial anode
Answer: c
Explanation: Cathodic protection is achieved by supplying electrons to the metal structure to be protected. Types of cathodic protection are i. External impressed current supply ii. Sacrificial anode.
5. Which of the following terminal of the power supply should be connected to the metal to be protected?
a) Negative terminal
b) Positive terminal
c) Both positive and negative terminals
d) Either positive or negative terminal
Answer: a
Explanation: As the conventional electrical theory states that current flows from to , the structure is protected if the negative terminal of the power supply is connected metallic structure.
6. Which of the following method is depicted in the given figure?
a) Anodic protection
b) Impressed current supply
c) Sacrificial anode
d) Anodic and cathodic protection
Answer: b
Explanation: Impressed current supply is a method of cathodic protection that is achieved by supplying electrons to the metal structure to be protected. The given figure depicted is impressed current supply method of an underground tank.
7. Which of the following material is/are used as an impressed-currents anode?
a) Graphite
b) Platinized titanium
c) Silicon-iron
d) Graphite, platinized titanium, and silicon-iron
Answer: d
Explanation: Materials that can be used as an impressed-currents anode are:
Graphite
Platinized titanium
Silicon-iron
Steel.
8. Which of the following materials is/are used as backfill around the anode in impressed currents?
a) Coke breeze
b) Gypsum
c) Bentonite
d) Coke breeze, gypsum, and bentonite
Answer: d
Explanation: Coke breeze, gypsum, and bentonite are the materials that are used as backfill material around the anode. These materials improve the electric contact between the anode and surrounding soil.
9. Which of the following protection method is depicted in the given figure?
a) Impressed-current supply method
b) Anodic protection
c) Sacrificial anode
d) Anodic protection and sacrificial anode
Answer: c
Explanation: Sacrificial anode method is one the type of cathodic protection in which a metal corrodes preferentially than the metallic structure. Sacrificial anodes are inexpensive and easily available in nature.
10. Which of the metallic structure will require more impressed current density for cathodic protection?
a) Water heaters in hot freshwater
b) Underground pipelines
c) The storage tank of H 2 SO 4
d) Reinforcement rods
Answer: c
Explanation: Impressed method current is an external supply of power to provide electrons to metallic structure that needs to be protected. The storage tank of H 2 SO 4 requires the highest current density per sq. feet due to the high corrosiveness of acid.
11. Which of the following reference electrode is used for cathodic-protection surveys?
a) Standard hydrogen electrode
b) Copper/copper sulfate reference electrode
c) Calomel electrode
d) Either calomel or standard hydrogen electrode
Answer: b
Explanation: Copper/copper sulfate reference electrode is used for cathodic protection surveys. The potential of a structure is determined with a high-resistance voltmeter. This electrode has the advantages of low cost, good accuracy, and ruggedness.
12. Which of the following is/are the typical sacrificial anodes?
a) Magnesium only
b) Zinc and magnesium
c) Aluminum-tin only
d) Magnesium, Zinc, and aluminum-tin
Answer: d
Explanation: Sacrificial anodes are metals that have a very high negative potential, which provides high current output. Magnesium, zinc, and aluminum-tin are typical examples of sacrificial anodes.
13. Which of the following is an impressed current anode that is efficient in a marine environment?
a) Platinized titanium
b) Silicon-iron
c) Scrap steel
d) Graphite
Answer: a
Explanation: Platinized titanium is an inert anode that is both efficient and expensive in nature. It is finding increased applications in marine environments.
14. Which of the following statements is/are correct about stray current?
a) It usually encountered in cathodic-protection systems
b) It refers to extraneous direct current in the earth
c) Acceleration corrosion will occur at the point where the current enters the soil
d) Stray current refers to extraneous direct current in the earth that usually encountered in cathodic protection systems and accelerated corrosion will occur at the point where current enters the soil
Answers: d
Explanation: Stray current refers to extraneous direct current in the earth that usually encountered in cathodic protection systems and accelerated corrosion will occur at the point where current enters the soil.
15. Which of the following is/are the preventions of stray current effect in an underground channel?
a) Use of bus conductor
b) Rearrangement of anodes
c) Use of bus conductor and rearrangement of anodes
d) Neither use of bus conductor nor rearrangements of anodes
Answer: c
Explanation: Stray current effect caused due to the densely buried underground pipelines in the vicinity of the cathodic protection system. It can be prevented by the use of bus conductors and rearrangements of anodes.
This set of Corrosion Engineering Questions and Answers for Campus interviews focuses on “Cathodic and Anodic Protection – 2”.
1. Which of the corrosion prevention method is used for reducing the maintenance cost of highway and bridges?
a) Sacrificial anode
b) Impressed current supply
c) Anodic protection
d) Use of inhibitors
Answer: b
Explanation: Impressed current supply is used as the corrosion prevention for reducing maintenance costs of big metallic structures such as highways and bridges. It also used to reduce the corrosion of reinforced steel.
2. Which of the following is depicted in the given figure?
a) Anodic protection
b) Impressed current supply
c) Stray current effect
d) Sacrificial anode
Answer: c
Explanation: The given figure depicts the stray current effect that usually caused to the dense pipelines in the vicinity of a tank or pipeline protected by the impressed current system.
3. Anodic protection is based on the formation of a protective film on metals by external applied anodic currents.
a) True
b) False
Answer: a
Explanation: Anodic protection is one of the corrosion prevention methods that is based on the formation of a protective film on metals by external applied anodic currents.
4. Which of the following metals can be protected using anodic protection?
a) Nickel and iron
b) Nickel, iron, and titanium
c) Titanium only
d) Nickel, iron, titanium, and magnesium
Answer: b
Explanation: Anodic protection can be used only for active-passive transition metals as it provides external current for the formation of a passive oxide layer. Active-passive transition metals include nickel, iron, aluminum, titanium, and its alloys.
5. A potentiostat is an electronic device that maintains a metal at a constant potential to a reference electrode.
a) True
b) False
Answer: a
Explanation: A potentiostat is an electronic device that maintains a metal at a constant potential to a reference electrode. It is required to protect a metal anodically by a passivating metal surface.
6. Which of the following corrosion prevention method is depicted in the given figure?
a) Sacrificial anode
b) Impressed current supply method
c) Use of inhibitors
d) Anodic protection
Answer: d
Explanation: Anodic protection of a storage tank is depicted in the given figure. A potentiostat is used to maintain the constant potential for a metallic structure against the reference electrode that results in passivity.
7. Which of the following auxiliary cathode is used for anodic protection?
a) Graphite
b) Platinized titanium
c) Platinum-clad electrode
d) Aluminum electrode
Answer: c
Explanation: It is necessary to have an inert auxiliary cathode such as a platinum-clad electrode as the anode provides external electric current to passivates the metallic structure.
8. Which of the following reference electrode is used in anodic protection?
a) Standard hydrogen electrode
b) Copper/copper sulfate reference electrode
c) Standard hydrogen electrode and calomel electrode
d) Calomel electrode
Answer: d
Explanation: The Calomel electrode is used to measure the potential maintained during the operation. It is connected to the third terminal of potentiostat whereas metal and auxiliary cathode are connected to first and second terminals respectively.
9. Which of the following is/are the advantages of anodic protection than cathodic protection?
a) Availability in extremely corrosive conditions
b) Low current requirement
c) Availability in extremely corrosive conditions and low current requirement
d) Very low installation cost
Answer: c
Explanation: Advantages of anodic protection than cathodic protection is:
i. Availability in extremely corrosive conditions
ii. Low current requirement.
10. Which of the following is/are the unique advantages of anodic protection?
a) To monitor instantaneous corrosion rate
b) Operating conditions can be established in the lab
c) It is applicable for all type of metals
d) To monitor instantaneous corrosion rate and operating conditions can be established in the lab
Answer: d
Explanation: Unique advantages of anodic protection are:
i. To monitor the instantaneous corrosion rate of a metal
ii. Operating condition of anodic protection can be precisely established in the lab.
This set of Corrosion Engineering Multiple Choice Questions & Answers focuses on “Corrosion Prevention – Coatings – 1”.
1. A thin coating of metallic and inorganic materials can provide a satisfactory barrier between the metal and its environment.
a) True
b) False
Answer: a
Explanation: A thin coating of metallic, inorganic, and organic material can provide a satisfactory barrier between the metal and its environment. Because it minimizes the exposure of native metal to the corrosive environment.
2. Which of the following is/are the purposes of coatings?
a) To acts as a sacrificial metal
b) To act as an effective barrier
c) Either to act as sacrificial metal or to act as an effective barrier
d) Neither to act as sacrificial metal nor to act as an effective barrier
Answer: c
Explanation: Coatings are the relatively thin material portion on the surfaces of native metal to avoid direct exposure to the corrosive environment. The purpose of coatings is either to act as sacrificial metal or to act as an effective barrier.
3. Which of the following is/are the methods to apply metallic coatings?
a) Electrode position
b) Flame spraying
c) Cladding
d) Electrode position, flame spraying, and cladding
Answer: d
Explanation: Methods to apply metallic coatings are:
i. Electrode position
ii. Flame spraying
iii. Cladding
iv. Hot dipping
v. Vapor deposition.
4. What is the reason for the localized attack on the base metal due to the porosity of coatings?
a) Crevice formation
b) Galvanic effect
c) Initiation of pits
d) Crevice formation and galvanic effect
Answer: b
Explanation: The localized attack on the base metal due to the porosity of coatings is dueto two-metal corrosion or galvanic effect. Because metal coating and base metal are electrically connected in a corrosive environment.
5. Which of the following is/are the examples for metal-coated articles?
a) Silverware
b) Galvanized steel
c) Tin cans
d) Silverware, galvanized steel, and tin cans
Answer: d
Explanation: Sacrificial metals such as zinc, tin, and precious metals such as silver, gold, platinum is used as metallic coatings for various applications. Silverware, galvanized steel, and tin cans are examples of metallic coatings.
6. What is meant by electrodeposition?
a) Immersing native metal in a solution of the metal to be plated
b) Hot rolling of two metals together to get a composite sheet
c) A wire or powder through melting flame is blown onto the surface to be protected
d) Coating metal is vaporized electrically to deposit on the metals to be coated
Answer: a
Explanation: Electrode position is an immersion of native metal in a solution of the metal to be plated with direct current passing through them. It is also called electroplating.
7. Which of the following is/are the factors of electroplating that effects efficiency?
a) Temperature and composition of the bath
b) Composition of bath and time
c) Temperature, the composition of the bath, time and current density
d) Current density and composition of the bath
Answer: c
Explanation: Factors that affect the efficiency of electroplating are:
i. Temperature
ii. Current density
iii. Time
iv. Composition of bath.
8. What is the general purpose of each coating in a three-layered coating of an automobile bumper?
a) Inner coating – adhesion, intermediate coating – corrosion protection and top layer – appearance
b) Inner coating – corrosion protection, intermediate coating – adhesion and top layer – appearance
c) All layers for corrosion resistance
d) All layers for appearance
Answer: a
Explanation: In general, multiple layered metallic structures consist of inner coating for adhesion such as copper, intermediate coating for corrosion resistance such as nickel and top coatings for appearance such as chromium.
9. What is meant flame spraying metallic coating?
a) Hot rolling of two metals together to get a composite sheet
b) A wire or powder through melting flame is blown onto the surface to be protected
c) Coating metal is vaporized electrically to deposit on the metals to be coated
d) Immersing native metal in a solution of the metal to be plated
Answer: b
Explanation: Flame spraying metallic coating is a method of metal coating in which a wire or powder through the melting flame is blown onto the surface to be protected. Oxygen, acetylene, and propane are used for melting flame.
10. Which of the following is/are the application of flame spraying?
a) Bridges
b) Refrigeration equipment
c) Ship hulls
d) Bridges, refrigeration equipment and ship hulls
Answer: d
Explanation: Application of flame spraying include vessels of all kinds, bridges, ship hulls, refrigeration equipment, and many fabricated steel products. Low melting point metals such as zinc, tin, and lead are used.
11. What is meant by metal cladding?
a) Immersing native metal in a solution of the metal to be plated
b) Coating metal is vaporized electrically to deposit on the metals to be coated
c) Hot rolling of two metals together to get a composite sheet
d) A wire or powder through melting flame is blown onto the surface to be protected
Answer: c
Explanation: Metal cladding is a method of hot rolling two metals together to get a composite sheet. High-strength aluminum alloys and commercial pure aluminum are rolled together to provide the corrosion barrier.
12. Cladding is a great economical advantage in that the corrosion barrier as the expensive material is backed up by inexpensive material by minimizing corrosion.
a) True
b) False
Answer: a
Explanation: Cladding is a great economical advantage in that the corrosion barrier as the expensive material is backed up by inexpensive material by minimizing corrosion.
13. What is meant by vapor deposition?
a) A wire or powder through melting flame is blown onto the surface to be protected
b) Coating metal is vaporized electrically to deposit on the metals to be coated
c) Hot rolling of two metals together to get a composite sheet
d) Immersing native metal in a solution of the metal to be plated
Answer: b
Explanation: Vapor deposition is a method of metal coating in that coating metal is vaporized electrically to deposit on the metals to be coated. It is usually used for high strength parts for missiles and rockets.
14. What is meant by diffusion coatings?
a) Immersing native metal in a solution of the metal to be plated
b) Coating metal is vaporized electrically to deposit on the metals to be coated
c) Heat treatment to cause alloy formation by diffusion of one metal into the other
d) Hot rolling of two metals together to get a composite sheet
Answer: c
Explanation: Diffusion coatings involve heat treatment to cause alloy formation by diffusion of one metal into the other. It is also called as surface alloying. It improves various properties such as wear-resistance and corrosion resistance at the surface.
15. Which of the following is/are the types of diffusion coatings?
a) Sherardizing – zinc
b) Chromizing – chromium
c) Alonizing – aluminum
d) Sherardizing – zinc, chromizing – chromium and alonizing – aluminum
Answer: d
Explanation: Types of diffusion coatings:
i. Sherardizing – zinc
ii. Chromizing – chromium
iii. Alonizing – aluminum
iv. Carburizing – carbon
v. Nitriding – nitrogen.
This set of Corrosion Engineering Assessment Questions and Answers focuses on “Corrosion Prevention – Coatings – 2”.
1. What is meant by chemical conversion regarding coatings of a metal?
a) Coating metal is vaporized electrically to deposit on the parts to be coated
b) Coatings produced by corroding the metal surface to form an adherent protective layer
c) Hot rolling of two metals together to produce composite sheet
d) A metal wire or powder through the melting flame is blown onto the surface to be protected
Answer: b
Explanation: Chemical conversion is one of the surface coating methods in that coatings are produced by corroding the metal surface to form an adherent protective layer.
2. Which of the following is/are the examples of chemical conversion?
a) Bonderizing
b) Parkerizing
c) Chromatizing
d) Bonderizing, parkerizing, and chromatizing
Answer: d
Explanation: Bonderizing, parkerizing, and chromatizing are examples of chemical conversion. Automobile bodies are best known for phosphatizing treatment. Anodized aluminum with a protective film Al 2 O 3 is another example.
3. In general, coatings should not be used where the environment would rapidly attack the substrate material.
a) True
b) False
Answer: a
Explanation: In general, coatings should not be used where the environments would rapidly attack the substrate material because one defect or small area of exposed metal would result in rapid degradation.
4. Which of the following is/are the examples of organic coatings?
a) Paints
b) Varnishes
c) Lacquers
d) Paints, varnishes and lacquers
Answer: d
Explanation: Organic coatings are widely used to protect more metals on a tonnage basis than other corrosion combating processes. Organic coatings include paints, varnishes, and lacquers.
5. Which of the following is/are factors to consider for organic coatings?
a) Surface preparation only
b) Surface preparation and selection of primary coating
c) Surface preparation and selection of primary and top coatings
d) Selection of primary and top coatings
Answer: c
Explanation: Factors to consider for organic coatings are:
i. Surface preparation usually is done by sandblasting
ii. Selection of primary coatings for strong adhesive bonding
iii. Selection of top coating for appearance and corrosion resistance.
6. What is the purpose of surface preparation?
a) Surface roughening for mechanical bonding
b) Removal of dirt, rust and mill scale
c) Removal of welding flux and other impurities
d) Surface roughening for mechanical bonding, removal of dirt, rust, mill scale, welding flux, and other impurities
Answer: d
Explanation: Surface preparation is a crucial part of the stability of coatings. It roughens the surface to obtain mechanical bonding, removal of dirt, rust, mill scale, welding flux, and other impurities.
7. Which of the following is/are the methods for surface preparation for coating application?
a) Sandblasting and chipping
b) Wire brushing and flame cleaning
c) Sandblasting, chipping, wire brushing and flame cleaning
d) Sandblasting, chipping and flame cleaning
Answer: c
Explanation: Methods for surface preparation for coating application are:
i. Sandblasting
ii. Wire brushing
iii. Flame cleaning
iv. Chipping
v. Scarping.
8. Which of the following paints are widely used for corrosion applications?
a) Vinyl and epoxy paints
b) Asphalts and bituminous paints
c) Iron oxide and titanium oxide paints
d) Alkyds and red lead
Answer: a
Explanation: A variety of paints are available in the market for various corrosion applications. It includes asphalts, bituminous paints, red lead, iron oxide, titanium oxide, alkyds, vinyl, and epoxies. Among them, vinyl and epoxies are the class of paints that are widely used for corrosion applications.
9. Which of the following is/are the characteristics of primers or primary coatings?
a) It contains rust-inhibitive pigments only
b) Adequate wettability and short drying time
c) Short drying time, adequate wettability and it contains rust-inhibitive pigments
d) It contains rust-inhibitive pigments and short drying time
Answer: c
Explanation: Characteristics of primary coatings are:
i. It contains rust-inhibitive pigments
ii. Adequate wettability
iii. Short drying time.
10. Which of the following is/are the advantages of coal-tar coatings?
a) Excellent corrosion resistance to fresh and seawater
b) Excellent corrosion resistant to fresh, seawater and soil immersion
c) High abrasive resistance
d) Stable coating
Answer: b
Explanation: Coal-tar coatings are excellent corrosion resistant to fresh, seawater, and soil immersion. Whereas its abrasive resistance and stability of coating are its limitations.
This set of Corrosion Engineering Multiple Choice Questions & Answers focuses on “Mineral Acids – Sulfuric Acid”.
1. Which of the following is/are the examples of mineral acids?
a) Sulfuric acid and nitric acid
b) Hydrochloric acid and hydrofluoric acid
c) Sulfuric, nitric, hydrochloric, hydrofluoric and phosphoric acid
d) Sulfuric, nitric, hydrochloric and hydrofluoric acid
Answer: c
Explanation: Mineral acid or inorganic acid is the acid derives from one or more inorganic compounds on dissolution with water. This includes sulfuric acid, nitric acid, hydrochloric acid, hydrofluoric acid, and phosphoric acid.
2. Which of the following acid is produced relatively higher than other acids?
a) Nitric acid
b) Sulfuric acid
c) Phosphoric acid
d) Hydrofluoric acid
Answer: b
Explanation: Sulfuric acid is produced relatively higher than other acids. The chemical formula for sulfuric acid is H 2 SO 4 . It is produced by absorbing water into oleum.
3. What are the principal uses of sulfuric acid?
a) Production of hydrochloric acid
b) Manufacturing of dyes, fertilizers, and drugs
c) Pickling of steels and other metals
d) Production of hydrochloric acid, manufacturing of dyes, fertilizers and drugs and pickling of steels
Answer: d
Explanation: Principle uses of sulfuric acid are:
Production of hydrochloric acid and other chemicals
Manufacturing of dyes, fertilizers, drugs, explosives, and rayon
Pickling of steels and other metals
Laboratory usage.
4. Which of the following method is used to produce sulfuric acid?
a) Contact process
b) Ostwald process
c) Solvay process
d) Haber process
Answer: a
Explanation: Sulfuric acid is produced by the contact process or leads chamber process. It is produced by absorbing SO 3 with water. This process accounts for 70% of world production.
5. Which of the following statements is/are true regarding the contact process?
a) Conversion of sulfur dioxide to sulfur trioxide takes place
b) Vanadium oxide is used as a catalyst
c) It accounts for 70% of the world’s production
d) Conversion of sulfur dioxide to sulfur trioxide takes place in the presence of vanadium catalyst and it accounts for 70% world’s production
Answer: d
Explanation: Contact process:
Sulfur compounds such as copper sulfide are burned to get SO 2
Catalytic conversion of sulfur dioxide to sulfur trioxide takes place
Absorption of SO 3 into water produces sulfuric acid.
6. Which of the following concentration of sulfuric acid in which the corrosion rate of steel is minimum?
a) Less than 30%
b) Greater than 70%
c) 30% – 70%
d) above 110%
Answer: b
Explanation: Ordinary steels are widely used for various concentrations of sulfuric acid greater than 70% purity. Dilute acids attack steel very rapidly and result in faster degradation.
7. Which of the following are the functions of the given graph on the x and y-axis respectively?
a) Temperature and concentration of acid
b) Corrosion rate and temperature
c) The concentration of acid and temperature
d) The concentration of acid and corrosion rate
Answer: c
Explanation: The given graph is an isocorrosion chart. It is a streamlined method devised to present the corrosion data. The concentration of acid and temperature are the functions of the isocorrosion chart on the x and y-axis respectively.
8. Which of the following is/are the factors that affect the corrosion resistance of steel in concentrated sulfuric acid?
a) High velocity
b) Temperature of acid
c) Aeration
d) High velocity, temperature, and aeration
Answer: d
Explanation: High velocity, the temperature of acid and aeration are the factors that affect the corrosion resistance of steel in concentrated sulfuric acid .
9. Which of the following metal is not corrosion resistant to sulfuric acid?
a) Grey cast iron
b) Duriron
c) Durimet 20
d) Lead
Answer: a
Explanation: Grey cast iron is not corrosion resistant to sulfuric acid as it penetrates the metal along with the graphite flakes. Though the corrosion rates are small but the metal may split open in service.
10. Lead is used extensively for sulfuric acid in the lower concentration ranges .
a) False
b) True
Answer: b
Explanation: Lead is used extensively for sulfuric acid in the lower concentration ranges . It is not recommended above 70% purity is due to the solubility of lead sulfate surface film in the acid.
11. Which of the following is/are the applications of Duriron because of its corrosion resistance and inherent hardness?
a) To manufacture pumps, valves, and fans
b) To make heat exchangers
c) Impressed–current anodes
d) To manufacture pumps, valves, fans, heat exchangers and impressed-current anodes
Answer: d
Explanation: Duriron is high-silicon cast iron with high corrosion resistance and inherent hardness. It is used to manufacture pumps, valves, fans, heat exchangers, and impressed-current anodes.
12. Which of the following alloying elements are not recommended in the sulfuric acid environment?
a) Chromium
b) Nickel
c) Molybdenum
d) Nickel and molybdenum
Answer: c
Explanation: Alloying elements are added in base metal to exhibit certain specific properties such as corrosion resistance, thermal properties, or mechanical properties. Here molybdenum is not recommended as an alloying element in high-silicon cast iron for sulfuric acid application.
This set of Corrosion Engineering Question Paper focuses on “Mineral Acids – Nitric Acid and Hydrochloric Acid”.
1. Which of the following is/are the class1 corrosion resistance materials in nitric acid?
a) High-silicon cast irons
b) Stainless steels
c) Titanium
d) High-silicon cast iron, stainless steels, and titanium
Answer: d
Explanation: Class1 materials are the materials that are used for a particular environment and it is generally recommended for a variety of conditions of temperature and concentration. Class1 materials for nitric acid includes high-silicon cast irons, stainless steels, and titanium.
2. Which of the following steels will have less corrosion rate in boiling 65% nitric acid?
a) 4.5% chromium steel
b) 8% chromium and 8% nickel steel
c) 18% chromium and 8% nickel stainless steel
d) 18% chromium stainless steel
Answer: c
Explanation: The corrosion resistance of steel in nitric acid increases as the alloying elements such as chromium and nickel increases. The minimum percentage of chromium required for adequate corrosion resistance is 15%.
3. Duriron exhibits excellent corrosion resistance in concentrations over 45% at temperatures including boiling.
a) True
b) False
Answer: a
Explanation: Duriron is high-silicon cast iron with 14.5% silicon exhibits excellent corrosion resistance in concentrations over 45% at temperatures including boiling. It is a class1 material in the usage of nitric acid.
4. The corrosion resistance of Durichlor to nitric acid is better than that of Duriron.
a) True
b) False
Answer: b
Explanation: Durichlor is high-silicon cast iron with 14.5% silicon and 3% molybdenum. It is not better corrosion resistant to nitric acid than that of Duriron. Because molybdenum doesn’t increase the corrosion resistance to nitric acid.
5. What are the principal applications of Duriron?
a) Cast forms of pumps, valves, heat exchangers for chemical plant
b) In manufacturing and handling of nitric acid
c) In the ammonia oxidation process
d) Cast forms of pumps, valves, heat exchangers for chemical plant, in manufacturing and handling of nitric acid and ammonia oxidation process
Answer: d
Explanation: Principal applications of Duriron are:
i. Cast forms of pumps, valves, heat exchangers for chemical plants
ii. In manufacturing and handling of nitric acid
iii. In the ammonia oxidation process.
6. Which of the following statements is/are true about titanium?
a) It has excellent corrosion resistance to fuming nitric acid
b) It is used as an oxidizer in fuel systems for rockets
c) It has excellent corrosion resistance to fuming nitric acid and it is used as an oxidizer in fuel systems for rockets
d) It doesn’t exhibit pyrophoric tendencies in red fuming nitric acid
Answer: c
Explanation: Titanium has excellent corrosion resistance to fuming nitric acid and it is used as an oxidizer in fuel systems for rockets. Whereas it exhibits pyrophoric tendencies in red fuming nitric acid if the water content of the acid is below 1.5% and the nitrogen dioxide content is above 2.5%.
7. Which of the following is/are the class2 corrosion-resistant materials in nitric acid?
a) Aluminum and Stainless steels
b) Aluminum, Hastelloy, and Inconel
c) Hastelloy and Inconel
d) Hastelloy and Titanium
Answer: b
Explanation: Class2 corrosive resistance materials of nitric acid are the materials that are used in only certain specific conditions of temperature and concentration because of limited corrosion resistance and cost. This includes Aluminum, Hastelloy, and Inconel.
8. Which of the following polymer has excellent corrosion resistance to nitric acid?
a) Teflon
b) Polyvinyl chloride
c) Polystyrene
d) Polyethylene
Answer: a
Explanation: Teflon shows excellent corrosion resistance to nitric acid. Glass filled Teflon is widely used for rotating rings in mechanical seals for nitric acid pumps.
9. Which of the following is/are the class3 corrosion-resistant materials in nitric acid?
a) Copper and its alloys
b) Nickel and its alloys
c) Low-alloy steels
d) Low-alloy steels, copper, nickels and their alloys
Answer: d
Explanation: Class3 materials are recommended for use in a particular environment because of its less corrosion resistance. This includes copper and its alloys, nickel and its alloys and low-alloy steels.
10. Which of the following metal is used for hydrochloric acid to avoid contamination?
a) Titanium
b) Tantalum
c) Molybdenum
d) Cupronickels
Answer: b
Explanation: Hydrochloric acid is the most difficult of the common acids to handle regarding corrosion. Tantalum is an expensive metal but it is often used to avoid contamination.
11. Which of the following is/are the class1 corrosion resistance materials in hydrochloric acid?
a) Chlorimet 2 and Chlorimet 3
b) Hastelloy B and C
c) Zirconium and molybdenum
d) Chlorimet 2 and 3, Hastelloy B and C, Zirconium, Molybdenum and Tantalum
Answer: d
Explanation: Class1 materials are the materials that are used for a particular environment and it is generally recommended for a variety of conditions of temperature and concentration. Class1 materials for hydrochloric acid include Chlorimet 2 and 3, Hastelloy B and C, Zirconium, Molybdenum, and Tantalum.
12. Duriron has better corrosion resistance than Durichlor in hydrochloric acid.
a) False
b) True
Answer: a
Explanation: Durichlor is high-silicon cast iron with 14.5% silicon and 3% molybdenum is more corrosion resistant than Duriron in hydrochloric acid.
13. Which of the following is/are the class2 corrosion resistance materials in hydrochloric acid?
a) Bronzes and Cupronickels
b) Hastelloy D and Duriron
c) Bronzes, Stainless steels, Bronzes, Cupronickels, Hastelloy D and Duriron
d) Stainless steels and Duriron
Answer: c
Explanation: Class2 corrosive resistance materials of nitric acid are the materials that are used in only certain specific conditions of temperature and concentration because of limited corrosion resistance and cost. This includes bronzes, stainless steels, bronzes, cupronickels, Hastelloy D, and Duriron.
14. Which of the following metals will have a high influence on aeration and oxidizing agents in hydrochloric acid?
a) Copper and its alloys
b) Nickel and its alloys
c) Nickel-molybdenum alloys, copper, nickel and their alloys
d) Nickel-molybdenum alloys
Answer: c
Explanation: Nickel-molybdenum alloys, copper, nickel, and their alloys will have a high influence on aeration and oxidizing agents in hydrochloric acid. These materials show excellent corrosion resistance in reducing conditions but are rapidly attacked in oxidizing conditions.
15. Which of the following impurity in hydrochloric acid results in pitting corrosion?
a) Ferrous chloride
b) Ferric chloride
c) Potassium chloride
d) Sodium chloride
Answer: b
Explanation: Ferric chloride in small amounts is more destructive than oxygen in hydrochloric acid. It initiates pits and results in pitting corrosion on various metals in the hydrochloric environment.
This set of Corrosion Engineering Multiple Choice Questions & Answers focuses on “Mineral Acids – Hydrofluoric Acid and Phosphoric Acid”.
1. Which of the following material is/are primarily used for hydrofluoric acid?
a) High-silicon cast iron
b) Magnesium
c) Aluminum
d) Glass and stoneware
Answer: b
Explanation: Materials such as high-silicon cast iron, aluminum, glass, and stoneware are generally resistant to many acids but these are readily attacked in hydrofluoric acid. Whereas magnesium is practically immune to corrosion because of the formation of a surface fluoride film.
2. Hydrofluoric acid and fluorine are toxic and extreme care are mandatory in the handling of these materials.
a) True
b) False
Answer: a
Explanation: Hydrofluoric acid and fluorine are toxic and extreme care are mandatory in the handling of these materials. Metals such as magnesium are used for some shipping containers because of the formation of a surface fluoride film.
3. Which of the following metal is suitable in handling high concentrations of hydrofluoric acid?
a) Stainless steel
b) Brass
c) Steel
d) Titanium
Answer: c
Explanation: Steel is suitable for handling hydrofluoric acid ranging concentration from 60% to 100%. The corrosion of steel rapidly increases as the concentration decreases below 60%.
4. Which of the following is/are the impurities in commercial hydrofluoric acid that decreases corrosion of steel?
a) Sulfuric acid
b) Fluosilicic acid
c) Neither sulfuric acid nor fluosilicic acid
d) Both sulfuric acid and fluosilicic acid
Answer: d
Explanation: Usually impurities such as sulphuric acid and fluosilicic acid are present in commercial hydrofluoric acid that reduces the corrosion of steel.
5. Which of the following metal is an outstanding material that resists all concentrations of hydrofluoric acid at all temperatures?
a) Wrought Monel
b) Steel
c) Stainless steel
d) Hastelloy C
Answer: a
Explanation: Wrought Monel is an outstanding metal in that it resists all concentrations of hydrofluoric acid at all temperatures including boiling. Monel is the best selection of material for hydrofluoric environment applications.
6. Why straight chromium stainless steels and austenitic stainless steels are not recommended for hydrofluoric acid applications?
a) Due to susceptibility to crevice
b) Due to limited corrosion resistance
c) Due to susceptibility to pitting
d) Sensitive to erosion-corrosion
Answer: c
Explanation: Straight chromium stainless steels and austenitic stainless steels are not recommended for hydrofluoric acid applications due to their susceptibility to pitting corrosion. Whereas of stainless steel is sensitive to erosion-corrosion.
7. Which of the following materials is/are widely used for phosphoric acid?
a) 316 stainless steel
b) Durimet 20
c) Neither 316 stainless steel nor Durimet 20
d) Both 316 stainless steel and Durimet 20
Answer: d
Explanation: 316 stainless steel and Durimet 20 are the two alloys that are widely used for phosphoric acid. These alloys show the very little attack in concentrations up to 85% and temperatures including boiling.
8. Which of the following materials exhibits poor corrosion resistance to phosphoric acid?
a) Aluminum and brass
b) Aluminum, brass, steel, cast iron, ferritic and martensitic stainless steels
c) Steel and cast iron
d) Ferritic and martensitic stainless steels
Answer: b
Explanation: Metals such as aluminum, brass, steel, cast iron, ferritic, and martensitic stainless steels exhibit poor corrosion resistance to phosphoric acid. Whereas 316 stainless steel and Durimet 20 are widely used for phosphoric acid.
9. Which of the following is/are the impurities that cause corrosion in commercial phosphoric acid?
a) Fluorides
b) Chlorides
c) Sulfuric acids
d) Fluorides, chlorides and sulfuric acid
Answer: d
Explanation: Corrosion by phosphoric acid depends on the methods of manufacturing and impurities present in that commercial acid. Impurities that are usually present in commercial phosphoric acid are fluorides, chlorides, and sulfuric acid.
10. Which of the following non-metallic has the highest corrosive resistance to the phosphoric acid with temperature?
a) Teflon
b) Graphite
c) Polyvinyl chloride
d) Polyethylene
Answer: a
Explanation: Teflon is a non-metallic material that has the highest corrosion resistance to phosphoric acid up to 550°C. Teflon is also known as polytetrafluoroethylene (CF 2 =CF 2 ).
This set of Corrosion Engineering Multiple Choice Questions & Answers focuses on “Environments – Organic Acids”.
1. Which of the following materials is/are used for handling acetic acid?
a) Type 316 and 304 Stainless steels
b) Copper and Bronzes
c) Duriron and Hastelloy C
d) Hastelloy C, Durimet 20, Duriron, Copper, Bronzes and 316 and 304 stainless steels
Answer: d
Explanation: Acetic acid is the most important organic acid from the standpoint of quantity produced. Hastelloy C, Durimet 20, Duriron, Copper, Bronzes, and 316 and 304 stainless steels are widely used for handling acetic acid.
2. Which of the following metals will switch positions in acetic acid as the temperature gets increased?
a) Copper and stainless steel
b) Stainless steel and nickel
c) Steel and copper
d) Aluminum and nickel
Answer: a
Explanation: Acetic acid exhibits unusual corrosion behavior with an increase in temperature. Copper and stainless-steel switch positions as the temperature are increased. Copper shows little corrosion at high temperatures whereas stainless steels corrode rapidly and vice versa.
3. Organic acids are relatively weaker than the inorganic acids because they are slightly ionized.
a) True
b) False
Answer: a
Explanation: Organic acids are relatively weaker than the inorganic acids because they are slightly ionized. The relatively high degree of ionization of inorganic acid results in greater electrochemical corrosion of metal.
4. Which of the following is the most corrosive organic acid?
a) Acetic acid
b) Formic acid
c) Ethanol
d) Acetone
Answer: b
Explanation: Formic acid is one of the strongest and most corrosive organic acids. It mainly results in stress-corrosion cracking of various metals at various conditions. The chemical formula of formic acid is HCOOH.
5. Which of the following metal is prone to stress corrosion cracking in methanol?
a) Nickel
b) Copper
c) Titanium
d) Stainless steel
Answer: c
Explanation: Methanol is the derivate of methane and it is also called methyl alcohol. The chemical of methanol is CH 3 OH. Titanium is prone to stress corrosion cracking in methanol with the presence of chloride impurities.
6. Which of the following metals will have high corrosion rates in aerated acetic acid?
a) Aluminum and its alloys
b) Copper and its alloys
c) Titanium and its alloys
d) Nickel and its alloys
Answer: b
Explanation: Copper and its alloys will be highly affected by aeration in acetic acid and it increases with an increase in temperature. It can be prevented by deaeration and decrease in temperature.
7. Which of the following impurities that affect the corrosion rate of carbon steel in benzene solvent?
a) Oxygen
b) Butyric acid
c) Oxygen and butyric acid
d) Zinc dust
Answer: c
Explanation: Oxygen and butyric acid are the impurities that affect the corrosion rate of carbon steel in benzene solvent. It can be prevented by eliminating oxygen.
8. What are the parameters that affect the corrosion rate of metal in organic acids?
a) Solvent composition
b) The solubility of corrosion products
c) Oxygen solubility
d) Solvent composition, the solubility of corrosion products and oxygen solubility
Answer: d
Explanation: Parameters that affect the corrosion rate of metals in organic acids are:
i. Solvent composition and structure
ii. The solubility of corrosion products
iii. Oxygen solubility.
9. Which of the following is/are the corrosion prevention methods in organic acids?
a) Selection of materials and drying
b) Selection of materials, drying, deaeration, and neutralization of the solvent
c) Deaeration and neutralization of the solvent
d) Drying and deaeration
Answer: b
Explanation: Corrosion prevention methods in organic acids:
i. Selection of materials
ii. Drying
iii. Deaeration
iv. Neutralization of the solvent.
10. The application of electrochemical protection methods in organic acids is restricted due to low electrical conductivity.
a) True
b) False
Answer: a
Explanation: Application of electrochemical protection methods in organic acids is restricted due to low electrical conductivity. As we know cathodic and anodic protection is based on electrical conductivities of metallic structure and medium.
This set of Corrosion Engineering Multiple Choice Questions & Answers focuses on “Environments – Alkalies”.
1. What is meant by caustic embrittlement?
a) Decrease in compressive strength due to caustic accumulation
b) The phenomenon of metal to become brittle due to caustic accumulation at the rivets
c) Entrapment of caustic content between atoms to cause brittleness
d) The phenomenon of metal to become more tensile due to caustic accumulation
Answer: b
Explanation: Caustic embrittlement is the phenomenon of metal to become brittle due to caustic accumulation at the rivets. The cold working of rivets is the main reason for caustic embrittlement.
2. Which of the following statements is/are correct regarding caustic embrittlement?
a) Mild carbon steels are susceptible to caustic embrittlement
b) It occurs in concentrated hydroxide environment
c) It occurs around the rivets
d) Mild carbon steels are susceptible to caustic embrittlement in concentrated hydroxide environment around the rivets
Answer: d
Explanation:
i. Mild carbon steels are susceptible to caustic embrittlement
ii. It occurs in concentrated hydroxide environment
iii. It occurs around the rivets due to cold working.
3. Which of the following is/are the preventions of caustic embrittlement?
a) Optimize stress concentration
b) Avoid caustic environment
c) Use of nickel-based alloys, avoid caustic environment and optimize stress concentration
d) Use mild carbon steels
Answer: c
Explanation: Preventions of caustic embrittlement are:
i. Optimize stress concentration
ii. Avoid caustic environment
iii. Use of nickel-based alloys.
4. Which of the following common alkalies that results in stress-corrosion cracking of steel?
a) Caustic soda
b) Caustic soda and caustic potash
c) Caustic potash
d) Sodium carbonate
Answer: b
Explanation: Caustic soda and caustic potash are the common alkalies that result in stress-corrosion cracking of steel. It usually occurs in high concentrations only.
5. Which of the following metal is suitable under all conditions of concentration and temperature in caustic soda?
a) Nickel
b) Aluminum
c) Titanium
d) Carbon steel
Answer: a
Explanation: Nickel is suitable under all conditions of concentrations and temperatures in the caustic environment. The corrosion resistance of material directly proportional to the nickel content of an alloy.
6. Aluminum is a very poor resistant material for handling caustic environments and rapidly attacked even by dilute solutions.
a) False
b) True
Answer: b
Explanation: Aluminum is a very poor resistant material for handling caustic environments and rapidly attacked even by dilute solutions. But it is adopted in an ammoniacal environment such as refrigeration systems and storage tanks.
7. Which of the following metal results in stress corrosion cracking in an ammoniacal solution?
a) Aluminum and its alloys
b) Nickel and its alloys
c) Copper and its alloys
d) Stainless steels
Answer: c
Explanation: Copper and its alloys result in stress corrosion cracking in ammoniacal solutions. The decomposition of organic materials containing nitrogen has caused stress corrosion cracking.
8. Oxygen is the primary cause of cracking in ammoniacal solution rather than nitrogen.
a) True
b) False
Answer: a
Explanation: Oxygen is the primary cause of cracking, with as little as 0.01 ppm required in the ammoniacal solution. A slip step or film rupture is a mechanical method of this cracking.
9. Which of the following can be used to inhibit stress corrosion cracking in ammoniacal solutions?
a) Addition of 0.2% water
b) Addition of 0.025% hydrazine in refrigeration
c) Addition of oxidizing agents
d) Either addition of 0.2% water or addition of 0.025% hydrazine in refrigeration
Answer: d
Explanation: Oxygen and oxidizing agents are the primary cause of stress corrosion cracking in ammoniacal solutions. It can be inhibited by the addition of 0.25% of water or the addition of 0.025% hydrazine in refrigeration.
10. Which of the following is/are used for ammoniacal solution applications?
a) Cast iron and steel
b) 430 and 304 type stainless steels
c) Cast iron, steel, 430 and 304 type stainless steels
d) Copper and cast irons
Answer: c
Explanation: Ammonia and ammoniacal solutions generally do not present a difficult corrosion problem. We usually use cast iron, steel, and 430, 304 type stainless steels for low and high temperatures respectively.
This set of Corrosion Engineering Multiple Choice Questions & Answers focuses on “ Environments – Atmospheric Corrosion”.
1. Which of the following is/are the classifications of atmospheres regarding atmospheric corrosion?
a) Industrial
b) Marine
c) Rural
d) Industrial, marine and rural
Answer: d
Explanation: Atmospheric corrosion can be defined as the corrosion of metals in surrounding corrosive environment. It can be classified into three types namely industrial, marine and rural atmospheres.
2. Which of the following is/are the primary causes of atmospheric corrosion?
a) Moisture
b) Oxygen
c) Moisture, oxygen and sulfur contaminants
d) Sulfur contaminants only
Answer: c
Explanation: The primary causes of atmospheric corrosion is moisture, oxygen and sulfur contaminants. Absence of either moisture or oxygen in at least form will result in no corrosion.
3. Corrosion of steel on the seacoast is 400 to 500 times is more corrosive than in a desert area.
a) True
b) False
Answer: a
Explanation: Corrosion of steel on the seacoast is 400 to 500 times is more corrosive than in a desert area. This due to the contamination of atmosphere with sodium chloride and other impurities at the seacoast.
4. How many times that industrial corrosion is more corrosive than rural atmospheres?
a) 10 to 20
b) 50 to 100
c) 30 to 50
d) 100 to 150
Answer: b
Explanation: Industrial corrosion is 50 to 100 times more corrosive than desert areas. It is due to the presence of Sulphur burned gases such as SO 2 , SO 3 and these results in the formation of sulfurous and sulfuric acids in the presence of moisture.
5. Which of the following is/are the reasons for more corrosiveness of industrial atmosphere than rural atmosphere?
a) Formation of sulfurous and sulfuric acid
b) Ejection of corrosive ammoniacal solutions
c) Formation of sulfurous and sulfuric acid and ejection of corrosive ammoniacal solutions
d) High levels of carbon dioxide
Answer: c
Explanation: Formation of sulfurous and sulfuric acid from sulfur burning gases and ejection of corrosive ammoniacal solutions are the reasons of industrial corrosion. Whereas carbon dioxide is not corrosive in nature.
6. Which of the following alloying elements increase resistance of steel to atmospheric corrosion?
a) Copper
b) Nickel
c) Chromium
d) Copper, nickel and chromium
Answer: d
Explanation: Steel is the most widely used metal for various metallic structures in all atmospheres. The resistance of steel can be improved by alloying elements such as copper, nickel and chromium. This is due to formation of stable, thick and adherent protective film.
7. Which of the following metals are widely used for atmospheric applications?
a) Copper and lead
b) Copper, lead, aluminum and galvanized steel
c) Galvanized steel only
d) Galvanized steel and copper
Answer: b
Explanation: Copper, lead, aluminum and galvanized steel are widely used for atmospheric corrosion applications. Improving the corrosion resistance of steel with small alloy additions is now commonly used along with weight-saving applications.
8. Which of the following alloys is also called as weathering steels?
a) Low-alloy steels used for atmospheric applications
b) High-alloy steels used for atmospheric applications
c) Low-alloy copper alloys
d) Low-alloy aluminum alloys
Answer: a
Explanation: Low-alloy steels used for atmospheric applications is also known as weathering steels. It is also used in weight-saving applications and to increase durability of paint coatings.
9. Sheltered corrosion is the type of corrosion where moisture condenses or accumulates and does not dry out for long periods of time.
a) False
b) True
Answer: a
Explanation: Sheltered corrosion is the type of corrosion where moisture condenses or accumulates and does not dry out for long periods of time. Corrosion on inside of an automobile door and inside of a partially filled automobile gasoline tank are the examples of sheltered corrosion.
10. Which of the following phenomenon that results in rapid corrosion on the inside of large storage tanks occurs when moisture-laden salt air is drawn in?
a) Sheltering
b) Breathing
c) Exhalation
d) Crevice
Answer: b
Explanation: Breathing results in rapid corrosion on the inside of large storage tanks occurs when moisture-laden salt air is drawn in. This can be prevented by protective coatings for steels and blanketing with nitrogen or dry air inside the tank.
This set of Basic Corrosion Engineering Questions and Answers focuses on “Environments – Sea Water and Fresh Water”.
1. Which of the following is/are true regarding seawater?
a) It contains 3.4% salt
b) It has a pH around 8
c) It is a good electrolyte with high electrical conductivity
d) Seawater is a good electrolyte with high electrical conductivity with 3.4% salt and pH around 8
Answer: d
Explanation: Seawater is a good electrolyte with high electrical conductivity with 3.4% salt and pH around 8. It can cause galvanic and crevice corrosion to various metals.
2. Which of the following is/are the factors that affect corrosion in seawater?
a) Temperature and velocity
b) Oxygen content and biological organisms
c) Temperature, velocity, oxygen content and biological organisms
d) Temperature, velocity and oxygen content
Answer: c
Explanation: The factors that affect the corrosion of materials in seawater are:
i. Temperature
ii. Velocity
iii. Oxygen content
iv. Biological organisms.
3. Which of the following region of the seacoast environment have high corrosion based on the given figure?
a) Quiet seawater
b) Splash region
c) High tide area
d) Mud line
Answer: b
Explanation: Greatest corrosion occurs in the splash region due to alternate wetting and drying and also aeration. We know oxygen and moisture are the primary requirements for corrosion of metals.
4. Which of the following regions of the seacoast environment shows the effect of the pitting of metals and alloys?
a) Quiet seawater
b) High tide region
c) Low tide region
d) Splash region
Answer: a
Explanation: Pitting is extremely localized corrosion which results in holes or cavities. Quiet seawater in the region of the seacoast environment that shows the effect of the pitting of metals and alloys. An increase in the velocity of a corrosive solution decreases the pitting tendency of a metal.
5. Corrosion by seawater at greater depth is usually decreased because of the lower temperature.
a) False
b) True
Answer: b
Explanation: Corrosion by seawater at greater depth is usually decreased because of the lower temperature. It decreases by 40°F for one-mile depth.
6. Which of the following impurities contaminates the brackish water due to tidal action in rivers and bays near the ocean?
a) Chlorides
b) Bromides
c) Hydrides
d) Metal oxides
Answer: a
Explanation: Chloride ions are the impurities that contaminate the brackish water due to the tidal action in rivers and bays near the ocean. The source of these chloride ions is sodium chloride in seawater.
7. Which of the following metals have high resistance to crevices in quiet seawater?
a) Hastelloy C
b) Titanium
c) Hastelloy C and Titanium
d) Nickel-copper alloy
Answer: c
Explanation: Hastelloy C and titanium have high resistance to crevices in quiet seawater. Due to this, these metals are used for various corrosive seawater applications. Whereas nickel-copper alloy shows less resistance.
8. Which of the following alloy has high cavitation resistance that usually used for ship propellers and pumps impellers in seawater?
a) Titanium
b) Stellite
c) 17-7 Stainless steel
d) Nickel aluminum bronze
Answer: b
Explanation: Stellite is a cobalt-chromium alloy with high cavitation resistance that usually used for ship propellers and pump impellers in seawater. Composition of Stellite is 27–32% chromium, 4–6% tungsten, 0.9–1.4% carbon, with additions of nickel, iron, silicon, manganese, and molybdenum and cobalt as balance.
9. Which of the following factors that affect the corrosivity in freshwater?
a) Oxygen content
b) Hardness
c) Chloride content
d) Oxygen content, hardness and chloride content
Answer: d
Explanation: Factors that affect the corrosivity in freshwater are:
i. Oxygen content
ii. Hardness
iii. Chloride and sulfur content.
10. Which of the following type of water is more corrosive?
a) Hard water
b) Hard and soft water
c) Soft water
d) High-purity water
Answer: c
Explanation: In hard water, carbonates often deposit on the metal surface and protect it from corrosion. Whereas in soft water protective deposits do not form. Hence, soft water is more corrosive than hard water and high-purity water.
11. Which of the following metals are widely used for handing freshwater?
a) Cast iron
b) Stainless steel
c) Galvanized steel
d) Cast iron, stainless steel, and galvanized steel
Answer: d
Explanation: Cast iron, stainless steel, steel, and galvanized steel are widely used for handling freshwater. Metals such as copper, brass, aluminum, monel, and cupronickels are also used with the factors of temperature, contamination, and longer life.
12. Which of the following corrosion defects that affect the reliability of tubing?
a) Selective weld metal attack
b) Improper pickling and heat treatment
c) Residual stresses, selective weld metal attack, improper pickling, and heat treatment
d) Selective weld metal attack and residual stresses
Answer: c
Explanation: Corrosion defects that affect the reliability of tubing are:
i. Inadequate alloying
ii. Selective weld metal attack
iii. Improper pickling
iv. Residual stresses
v. Improper heat treatment.
13. Corrosion decreases with an increase in the purity of water.
a) True
b) False
Answer: a
Explanation: Corrosion decreases with increasing purity of the water because of less solid and gases and increasing electrical resistance. Resistance is a measure of water purity.
14. Which of the following types of corrosion has been seen in stainless steels in high purity water containing oxygen?
a) Cracking of solution-quenched stainless steel only
b) Intergranular attack and cracking of solution-quenched steel
c) Intergranular attack only
d) Neither intergranular corrosion nor cracking of solution-quenched steel
Answer: b
Explanation: Intergranular corrosion and cracking of solution-quenched stainless steel and alloys have been observed in high-purity water containing oxygen.
15. Which of the following metals/alloys are used for handling high-purity water in nuclear applications?
a) Zirconium and its alloys
b) Stainless steels
c) Inconel and Incoloy
d) Zirconium and its alloys, stainless steels, Inconel and Incoloy
Answer: d
Explanation: Zirconium and its alloys, stainless steels, Inconel and Incoloy are the metals/alloys that are used for handling high-purity water in nuclear applications.
This set of Corrosion Engineering Multiple Choice Questions & Answers focuses on “Environments – Soil and Aerospace”.
1. The corrosivity of soils varies over a wide range because of the variety of composition.
a) True
b) False
Answer: a
Explanation: The corrosivity of a particular solution depends on its composition. So, the corrosivity of soils varies over a wide range because of the variety of composition.
2. Which of the factors that affect the corrosiveness of soils?
a) Moisture
b) Acidity
c) Oxygen
d) Moisture, oxygen, acidity and stray currents
Answer: d
Explanation: The factors that affect the corrosiveness of soils are moisture, oxygen, acidity, alkalinity, the permeability of air and water, stray currents, and biological organisms.
3. Which of the following is a good measure of corrosivity?
a) Thermal conduction
b) Electrical resistance
c) Thermal resistance
d) Mechanical properties
Answer: b
Explanation: Electrical resistance is a good measure of corrosivity of a corrosive solution. Higher electrical resistance lowers the corrosivity of a solution. Dry soils are generally not very corrosive due to high electrical resistance.
4. Which of the following type of corrosion is/are dominant due to backfills such as stones, cinders, wood, and metal?
a) Crevice corrosion
b) Pitting corrosion
c) Crevice and pitting corrosion
d) Neither crevice nor pitting corrosion
Answer: c
Explanation: Crevice and pitting corrosion are the types of corrosion that dominate due to backfill such as stones, cinders, wood, and metal. Because these foreign particles result in the formation of crevices.
5. Which of the following is/are true regarding underground structures?
a) Ordinary carbon steels and cast irons are commonly used
b) Organic coatings can be used
c) Cathodic protection is applied to protect it from corrosion
d) Usually made of carbon steel and cast irons with or without organic coatings and supported by a cathodic protection system
Answer: d
Explanation: Underground structures are usually made up of ordinary carbon steels and cast irons with or without organic coatings. These structures are also supported by a cathodic protection system to minimize corrosion.
6. Which of the following type of corrosion is pre-dominate in underground corrosion?
a) Aerobic corrosion
b) Anaerobic corrosion
c) Aerobic and anaerobic corrosion
d) Neither aerobic nor anaerobic corrosion
Answer: c
Explanation: The anaerobic type of attack is pre-dominate in underground corrosion. It is due to the non-availability of oxygen as it decreases with an increase in depth.
7. Which of the following areas of aircrafts face severe corrosion problems?
a) Fuel tank due to oxidizers and fuel
b) High-temperature corrosion in blast nozzles
c) The outer structure of the plane due to vacuum
d) Fuel tank due to oxidizers and fuel, high-temperature corrosion in blast nozzles
Answer: d
Explanation: Fuel tank due to oxidizers and fuel and high-temperature corrosion in blast nozzles are the two areas that aerospace face severe corrosion problems. Whereas the hard vacuum of space does not cause corrosion.
8. Which of the following materials is/are used for blast nozzles in aerospace?
a) Aluminum oxide and cemented tungsten carbide
b) Aluminum oxide cemented tungsten carbide and boron carbide
c) Cemented tungsten carbide only
d) Aluminum oxide and boron carbide
Answer: b
Explanation: Aluminum oxide, cemented tungsten carbide, and boron carbide is the materials that are used for blast nozzles in aerospace. These materials are also known as refractory materials.
9. Which of the following is/are the prime considerations in space vehicles and aircraft?
a) High strength-weight ratios for materials and high ratios of payload to the vehicle’s weight
b) High strength-weight ratios for materials only
c) High ratios of payload to vehicles weight only
d) Neither high strength-weight ratios for materials nor high ratios of payload to the vehicle’s weight
Answer: a
Explanation: High strength-weight ratio for materials and high ratios of payload to vehicle weight are the two prime considerations in space vehicles and aircraft.
10. Rusting of high-strength steel due to resident water can cause stress-corrosion and hydrogen embrittlement.
a) False
b) True
Answer: b
Explanation: Rusting of high-strength steel due to resident water can cause stress-corrosion and hydrogen embrittlement. Hydrogen charging of steel during electroplating can cause a brittle fracture.
11. Which of the following is/are the primary materials regarding the construction of aircraft?
a) Aluminum
b) Magnesium and titanium
c) Aluminum, magnesium, titanium, and iron
d) Titanium and magnesium
Answer: c
Explanation: Aluminum, magnesium, titanium, and iron and their alloys are the primary materials regarding the construction of aircraft. These are selected based on a high strength-weight ratio for materials and high ratios of payload to vehicle weight.
12. Which of the following corrosion protective systems is/are included in aircraft industries?
a) Anodizing, cladding and conversion coatings
b) Anodizing and cathodic protection
c) Conversion coatings and anodizing
d) Cathodic protection only
Answer: a
Explanation: Anodizing, cladding, and conversion coatings are the corrosive protective systems used in aircraft industries. Whereas cathodic protection cannot be used in the aircraft industry due to non-conductive electrolytes.
This set of Corrosion Engineering Multiple Choice Questions & Answers focuses on “ Environments – Petroleum Industry”.
1. Which of the following is/are the general areas of the petroleum industry that faces corrosion problems?
a) Production unit
b) Transportation and storage
c) Refinery operations
d) Production unit, transportation, storage, and refinery operations
Answer: d
Explanation: The Petroleum industry is one of the most affected industries with corrosion. The general areas of the petroleum industry that faces corrosion problems are production unit, transportation, storage, and refinery operations.
2. Which of the following impurities is often present in oil and gas wells?
a) Saline water
b) Sulfides
c) Saline water, sulfides and organic impurities such as ammonia
d) Organic impurities such as ammonia
Answer: c
Explanation: Oil and gas fields consumes a tremendous amount of iron and steel pipe, tubing, casings, pumps, and valves. Saline water, sulfides, and organic impurities such as ammonia are the impurities that are usually present in oil and gas fields.
3. How the corrosion characteristics of a well can be determined?
a) Inspection of surface equipment
b) Analysis of carbon dioxide and organic acid
c) Tubing-caliper surveys
d) Inspection of surface equipment, analysis of carbon dioxide, organic acid and tubing-caliper surveys
Answer: d
Explanation: Corrosion characteristics of a well is determined by
i. Inspection of surface equipment
ii. Analysis of carbon dioxide and organic acid
iii. Coupon exposure tests
iv. Tubing-caliper surveys.
4. Which of the following is/are the neutralizers added to well to minimize corrosion?
a) Ammonia and Sodium carbonate
b) Ammonia, sodium carbonate, sodium hydroxide, and sodium silicate
c) Ammonia and sodium silicate
d) Sodium carbonate and sodium silicate
Answer: b
Explanation: Neutralizers that are added to petroleum to minimize corrosion are:
i. Ammonia
ii. Sodium carbonate
iii. Sodium hydroxide
iv. Sodium silicate and some organic inhibitors.
5. Which of the following metals is/are used for petroleum well valves and wellhead parts?
a) Straight chromium stainless steels and stellite
b) Monel and copper-based alloys
c) Monel, straight chromium steels, stellite, and copper-based alloys
d) Monel and stellite
Answer: c
Explanation: Metals that are usually used for petroleum well valves and wellhead parts are straight chromium stainless steels, stellite, monel, and copper-based alloys.
6. Which of the following prevention methods that are usually employed on a beam of offshore drilling?
a) Paints and other organic coatings
b) Cathodic protection with sacrificial anodes or impressed currents
c) Adding inhibitors
d) Adding inhibitors, paints and other organic coatings and cathodic protection
Answer: d
Explanation: Preventions methods that are usually employed on a beam of offshore drilling are:
i. Paints and other organic coatings
ii. Cathodic protection with sacrificial anodes or impressed currents
iii. Adding inhibitors.
7. Which of the following inhibitor has been effective for internal corrosion domestic fuel oil tanks?
a) Alkaline sodium chromate
b) Sodium silicate
c) Ammonia
d) Sodium carbonate
Answer: a
Explanation: Alkaline sodium chromate or sodium nitrate is an effective inhibitor for the corrosion of domestic fuel oil tanks. The chemical formula of sodium chromate is Na 2 CrO 4 .
8. Which of the following impurities that causes corrosion difficulties in refinery operations?
a) Hydrogen sulfide and carbon dioxide
b) Hydrogen sulfide, carbon dioxide, sulfuric acid, and sodium chloride
c) Sodium carbonate and sodium silicate
d) Hydrogen sulfide and sulfuric acid
Answer: b
Explanation: Refinery of crude is done based on the difference in boiling points of the components present and the process is known as fractional distillation. Hydrogen sulfide, carbon dioxide, sulfuric acid, and sodium chloride are the impurities that cause difficulties in refinery operations.
9. Water acts as an electrolyte and causes corrosion as it tends to hydrolyze chlorides and other materials to form an acidic environment.
a) True
b) False
Answer: a
Explanation: Water acts as an electrolyte and causes corrosion in refining operations. This is because water tends to hydrolyze chlorides and other materials to form acidic environments.
10. Which of the following is/are the desalting methods in the petroleum industry?
a) Washing and settling
b) Addition of chemicals such as sulfonates
c) Centrifuging and filtering, washing and settling, the addition of chemicals such as sulfonates
d) Centrifuging and filtering
Answer: c
Explanation: Desalting methods in the petroleum industry are:
i. Washing and settling
ii. Addition of chemicals such as sulfonates
iii. Centrifuging and filtering.
11. Ammonia is used to control the pH of the water and to reduce chloride acidity in the process stream.
a) True
b) False
Answer: a
Explanation: Ammonia is used to control the pH of the water and to reduce chloride acidity in the process streams. It usually maintains a pH of 7 but it damages copper-bearing alloys if the pH becomes 8 or more.
12. Which of the chemical is/are added for the removal of hydrogen sulfide and neutralization?
a) Sodium hydroxide
b) Lime
c) Sodium hydroxide and lime
d) Naphthenic acid
Answer: c
Explanation: Sodium hydroxide and lime are/are added for the removal of hydrogen sulfide and neutralization during the refining of petroleum. NaOH and CaO are the chemical formulae of sodium hydroxide and lime respectively.
13. Which of the following impurity that causes rapid intergranular stress corrosion cracking of sensitized austenitic stainless steels in refinery operations?
a) Sodium chloride
b) Naphthenic acid
c) Hydrogen sulfide
d) Carbon dioxide
Answer: b
Explanation: Naphthenic acid causes rapid intergranular stress corrosion cracking of sensitized austenitic stainless steels in refinery operation. Whereas naphthenic acid is a combination of cyclopentyl and cyclohexyl carboxylic acids.
14. Which of the following metals is/are usually used for heat exchanger tubes carrying water?
a) Carbon steels
b) Brass and cupronickels
c) Arsenical admiralty metal
d) Brass, cupronickels and arsenical admiralty metal
Answer: d
Explanation: Brass, cupronickels, and arsenical admiralty metal are usually used for heat exchangers tubes carrying water. Whereas carbon steels are unsuitable as it rapidly corrodes by the cooling water.
Answer: a
Explanation: Chromium is the most beneficial alloying element in steel for resistance to sulfur compounds. As per the study, 2.25% chromium and 1% molybdenum is required for less than 0.2% H 2 S in the gas.
Sanfoundry Global Education & Learning Series – Corrosion Engineering.
This set of Corrosion Engineering Multiple Choice Questions & Answers focuses on “Environments – Biological Corrosion”.
1. Biological corrosion is a deterioration of a metal by the corrosion process that occurs directly or indirectly due to the activity of living organisms.
a) True
b) False
Answer: a
Explanation: Biological corrosion is a deterioration of a metal by the corrosion process that occurs directly or indirectly due to the activity of living organisms. This includes micro and microorganism.
2. Which of the following environments in which the biological activity may influence corrosion?
a) Soil
b) Fresh and seawater
c) Petroleum products
d) Soil, freshwater, seawater and petroleum products
Answer: d
Explanation: Biological activity will influence the corrosion of materials in a variety of environments including soil, freshwater, seawater, and petroleum products. These living organisms are sustained by chemical reactions.
3. Which of the following is/are the processes that affect the corrosion behavior of metals by biological activity?
a) By influencing anodic and cathodic reactions
b) By influencing protective surface films
c) By producing deposits, by influencing anodic, cathodic reactions and protective surface films
d) By creating non-corrosive conditions
Answer: c
Explanation: The process that affects the corrosion behavior of metals by biological activity are:
i. By directly influencing anodic and cathodic reactions
ii. By influencing protective surface films
iii. By creating a corrosive environment
iv. By producing deposits.
4. Which of the following component is taken into account to classify aerobic and anaerobic organisms?
a) Nitrogen
b) Oxygen
c) Argon
d) Phosphorus
Answer: b
Explanation: Percentage or relative amount of oxygen in the environment is taken into account to classify the microorganisms into aerobic and aerobic bacteria. The anaerobic attack is pre-dominate in underground corrosion due to the non-availability of oxygen.
5. Which of the following organisms are regarded as microorganisms?
a) Bacteria
b) Fungi
c) Protozoa
d) Bacteria, fungi, protozoa, and nematodes
Answer: d
Explanation: Bacteria, fungi, protozoa, and nematodes are one of the microorganisms usually present in the soil. Biological activity that directly or indirectly affects the corrosion of metals is known as biological corrosion.
6. Which of the following anaerobic bacteria that influence the corrosion behavior of buried steel structures?
a) Sulfur-reducing bacteria
b) Sulfur-oxidizing bacteria
c) Thiobacillus thiooxidans
d) Sulfur-reducing and sulfur-oxidizing bacteria
Answer: a
Explanation: Sulfur-reducing anaerobic bacteria influences the corrosion behavior of buried steel structures. SO 4 -2 +4H 2 ==>S -2 +4H 2 O is the general chemical reaction of sulfur-reducing anaerobic bacteria.
7. Thiobacillusthiooxidans are the type of aerobic bacteria that are capable of oxidizing sulfur-bearing compounds to sulfuric acid.
a) False
b) True
Answer: b
Explanation: Thiobacillusthiooxidans are the type of aerobic bacteria that are capable of oxidizing elemental sulfur and sulfur-bearing compounds to sulfuric acid. 2S+3O 2 +2H 2 O==>2H 2 SO 4 is the general chemical reaction of sulfur-oxidizing bacteria.
8. Which of the following coatings is/are used for the prevention of microbiological corrosion in buried steel?
a) Asphalt
b) Enamel
c) Plastic tape
d) Asphalt, enamel and plastic tape
Answer: d
Explanation: Microbiological corrosion influences the corrosion of buried steel structures in soil. This can be prevented by coatings such as asphalt, enamel, and plastic tape.
9. Which of the following is/are the preventions of microbiological corrosion in soil?
a) Use of substitute materials
b) Use of inhibitors
c) Applying coatings, use of inhibitors, cathodic protection and substitute materials
d) Cathodic protection
Answer: c
Explanation: Preventions to microbiological corrosion in soil:
i. Use of substitute materials such as asbestos and plastic
ii. Use of coatings such as asphalts and enamel
iii. Use of inhibitors and germicides
iv. Cathodic protection can be applied.
10. Which of the following acids are produced by microorganisms such as fungus and mold?
a) Oxalic acid
b) Lactic acid
c) Acetic acid
d) Oxalic acid, lactic acid, acetic acid, and citric acid
Answer: d
Explanation: Macroorganisms such as fungus and mold are also capable of influencing corrosion of metals in many environments. They assimilate organic matter and can produce considerable amounts of acids such as oxalic acid, lactic acid, acetic acid, and citric acid.
11. Which of the following materials is/are usually attacked by fungus?
a) leathers
b) Rubbers
c) Leathers, rubbers and bare and coated metals
d) Bare and coated metals
Answer: c
Explanation: Materials that are usually attacked by fungus are leathers, rubbers, and bare and coated metals. Though the attack of fungus on materials may not affect many mechanical properties it deteriorates the appearance of materials.
12. Which of the following is/are the preventions for the growth of mold on metal surfaces?
a) Periodic cleaning and storing in the high humid atmosphere
b) Periodic cleaning, reducing relative humidity during storage and applying toxic organic agents
c) Reducing relative humidity during storage and applying toxic organic agents
d) Periodic cleaning and reducing relative humidity during storage
Answer: b
Explanation: Preventions for the growth of mold on metal surfaces are:
i. Periodic cleaning of metal surfaces
ii. Reducing relative humidity during storage
iii. Applying toxic organic agents.
Answer: a
Explanation: Aqueous organisms such as barnacles, mussels, and algae influence the corrosion of metals in water. This includes an increase in the requirement of power for a severely fouled ship and limits heat transfers in heat exchangers.
Sanfoundry Global Education & Learning Series – Corrosion Engineering.
This set of Corrosion Engineering written test Questions & Answers focuses on “Environments – Liquid Metals and Fused Salts”.
1.The liquid-metal corrosion is usually a physical effect rather than an electrochemical attack.
a) True
b) False
Answer: a
Explanation: Liquid metal corrosion is usually a physical effect rather than an electrochemical attack. Electrochemical attack includes reduction and oxidation of hydrogen ions and metallic atoms respectively.
2. Which of the following is/are the types of liquid-metal corrosion?
a) Solution of structural metal
b) Diffusion of liquid into solid metal
c) Intermetallic compound formation
d) Solution of structural metal, diffusion of liquid into solid metal and intermetallic compound formation
Answer: d
Explanation: Types of liquid-metal corrosion are:
i. Solution of structural metal
ii. Diffusion of liquid into solid metal
iii. Intermetallic compound formation
iv. Mass transfer.
3. Which of the following is/are undesirable in heat-exchange systems handling liquid metals?
a) Deposition of impurities in cool areas
b) Resistance to heat transfer
c) Formation of brittle intermetallic compounds, resistance to heat transfer and deposition of impurities in cool areas
d) Formation of brittle intermetallic compounds
Answer: c
Explanation: Conditions that are undesirable in heat-exchange systems handling liquid metals:
i. Deposition of impurities in cool areas
ii. Resistance to heat transfer
iii. Formation of brittle intermetallic compounds.
4. Which of the following parameter has a direct relation with the corrosion rate in liquid metals?
a) Percentage of alloying elements
b) Solubility of the metallic structure in liquid metal
c) Solubility of alloying elements in metallic matrix
d) Percentage of oxygen
Answer: b
Explanation: Solubility of alloying elements in metallic matrix has direct relation with corrosion rate in liquid metals. Whereas liquid-metal corrosion is a physical effect rather than a chemical effect.
5. Which of the following parameter is taken as Xin the given graph regarding corrosion of various metals in liquid-metal corrosion?
a) Atomic weight
b) Weight loss
c) Solubility percentage
d) Atomic number
Answer: c
Explanation: The given graph shows the direct relation of corrosion rate with solubility of metallic structures in liquid mercury for various metals. And solubility of the metallic component in liquid mercury is taken as x.
6. Which of the following materials shows good resistance to both liquid-metals and high-temperature oxidation?
a) High alloy stainless steels
b) Monel
c) Hastelloy
d) Hastelloy, high alloy stainless steels and monel
Answer: d
Explanation: Materials that show good resistance to both liquid-metals and high-temperature oxidation are 18Cr-8Ni stainless steel, high alloy stainless steel, monel, and Hastelloy.
7. Which of the following type of stainless steels are attacked by magnesium at its melting point?
a) Duplex stainless steels
b) Austenitic stainless steels
c) Martensitic stainless steels
d) Ferritic stainless steels
Answer: b
Explanation: Austenitic stainless steels are the types of stainless steels that are attacked by magnesium at its melting. Liquid magnesium preferentially leaches out nickel from this alloy from the iron matrix.
8. The presence of traces of titanium and magnesium in mercury can inhibit the corrosion of iron in ferrous-based alloys.
a) True
b) False
Answer: a
Explanation: Traces of titanium and magnesium in mercury can inhibit the corrosion of iron in ferrous-based alloys. And it is reliable to use carbon steel in mercury for up to 540°C.
9. Which of the following materials have superior corrosion resistance and high rupture strength in mercury?
a) 5% chromium steels
b) Si-Cr-Mo steels
c) 5% chromium steels and Si-Cr-Mo steels
d) Carbon steels
Answer: c
Explanation: Now-a-days 5% chromium steels and Si-Cr-Mo steels replace carbon steels in mercury due to its superior corrosion resistance and high rupture strength.
10. Which of the following type of corrosion Is usually encounters for various materials in liquid metal environment?
a) Uniform corrosion
b) Stress cracking corrosion
c) Crevice corrosion
d) Pitting corrosion
Answer: b
Explanation: Stress cracking corrosion is a type of corrosion that usually encountered in various materials in a liquid metal environment. This is due to the chemisorption of liquid-metal atoms and a reduction in tensile strength at the crack tip.
11. Which of the following alloys is/are usually used for sodium hydroxide fused salt?
a) Nickel-based alloys
b) Copper-based alloys
c) Ferrous alloys
d) Zinc based alloys
Answer: a
Explanation: Sodium hydroxide is the most commonly used fused salt. And nickel-based alloys show good corrosion resistance to sodium hydroxide environment.
12. Which of the following is/are the types of mass transfer due to liquid-metal corrosion?
a) Composition-gradient mass transfer
b) Thermal-gradient mass transfer
c) Neither composition nor thermal gradient mass transfer
d) Both composition and thermal gradient mass transfer
Answer: d
Explanation: Types of mass transfer due to liquid-metal corrosion are:
i. Composition-gradient mass transfer
ii. Thermal-gradient mass transfer.
13. Which of the following types of steel coatings is/are preferred for automobile body parts?
a) Galvanized steels
b) Electroplated steels
c) Galvanized steels, electroplated steels and complete immersion of corrosion preventing primer coat
d) Complete immersion of corrosion preventing primer coat
Answer: c
Explanation: Types of steel coatings that are preferred for automobile parts are:
i. Galvanized steels
ii. Electroplated steels
iii. Complete immersion of corrosion preventing primer coat.
Answer: d
Explanation: Preventive measures to minimize automobile corrosion are:
i. Use of inhibitor in the engine cooling system
ii. Avoid very short runs
iii. Fill the gasoline tank at least half full.
Sanfoundry Global Education & Learning Series – Corrosion Engineering.
This set of Corrosion Engineering Multiple Choice Questions & Answers focuses on “Modern Theory Principles – Thermodynamics – 1”.
1. Which of the following is/are the applications of modern electrode kinetic principles?
a) Anodic protection
b) Noble metal alloying
c) Methods to measure corrosion rates rapidly
d) Anodic protection, noble metal alloying and methods to measure corrosion rates rapidly
Answer: d
Explanation: Modern electrode kinetics deals with electrochemical corrosion of aqueous solution and it results in the applications of
Anodic protection
Noble metal alloying
Methods to measure corrosion rates rapidly.
2. What is the direct measure of work capacity or electrical energy available from a system?
a) Change in enthalpy
b) Change in Gibbs free energy
c) Reaction time
d) Concentration of reactants
Answer: b
Explanation: Change is Gibbs free energy is the difference of free energies of the reaction products and reactants. And it is a direct measure of the work capacity or maximum electrical energy available in from a system.
3. If the transition of a system from one state to another state resulted in negative free energy change then it is known as a spontaneous reaction.
a) True
b) False
Answer: a
Explanation: If the transition of a system from one state to another state resulted in negative free energy change then it is known as a spontaneous reaction. It means the free energy of products is less than the free energy of reactants.
4. Which of the following is true, if the transition of a system results in positive Gibbs free energy change?
a) It is a spontaneous reaction
b) Free energy of products is less
c) It is a non-spontaneous reaction
d) Free energy of reactants is more
Answer: c
Explanation: If the transition of a system from one state to another state resulted in positive free energy change then it is known as a non-spontaneous reaction. It means the free energy of reactants is less than the free energy of products. It requires external heat or force to proceeds with the reaction.
5. Which of the following is a spontaneous reaction?
a) Production of ammonia
b) Corrosion of metals
c) Photosynthesis reaction
d) Generation of oxygen from water
Answer: b
Explanation: Spontaneous reaction is a reaction in which the reactants convert into products without any supply of external energy. Oxidation of metal atoms into metal ions due to the instability of metallic atoms is known as the corrosion of metals.
6. The change in Gibbs free energy is a path function and it is independent of the state of the system.
a) False
b) True
Answer: a
Explanation: The change in Gibbs free energy is a state function and it is independent of the path followed by the system to reach that state. It is denoted by ΔG .
7. Which of the following formula is used to calculate the Gibbs free energy of an electrochemical reaction?
a) ΔG=-nFE 0 cell
b) ΔG=+nFE 0 cell
c) ΔG=-nFE cell
d) ΔG=+nFE cell
Answer: c
Explanation: ΔG=-nFE cell where n is the electrons participated in the reaction, F is the faraday constant , E cell is the overall cell potential and E 0 cell is the standard cell potential.
8. What is the change in Gibb’s free energy of a Cu-Zn system with a cell potential of 1.10V?
a) -11.13 KJ/mol
b) +21.23 KJ/mol
c) +11.13 KJ/mol
d) -21.23 KJ/mol
Answer: d
Explanation: Given, Cell potential = 1.10V
n=number of electrons involved in reaction = 2
F=96500 coulombs
We know, ΔG=-nFE cell
ΔG=-2*96500*1.10
ΔG=-21.23 KJ/mol
9. Which of the following is/are correct regarding the given figure?
a) It is a reversible cell with unit activity
b) Copper and zinc are cathode and anode respectively
c) It is a reversible cell of Cu-Zn system with standard cell potential of 1.10V, copper and zinc are cathode and anode respectively
d) The standard cell potential is 1.10V
Answer: c
Explanation: Given figure represents a Cu-Zn system with standard cell potential of 1.10V. Copper and Zinc are cathode and anode respectively. Whereas two half-cells are separated by a porous membrane.
10. What are the cathodic and anodic reactions respectively of a given Cu-Zn system?
a) Cu==>Cu +2 +2e and Zn +2 +2e==>Zn
b) Cu +2 +2e==>Cu and Zn==>Zn +2 +2e
c) Cu==>Cu +2 +2e and 2Zn +1 +2e==>2Zn
d) Cu +2 +2e==>Cu and 2Zn==>2Zn +1 +2e
Answer: b
Explanation: As the standard hydrogen potential of copper is relatively higher than standard hydrogen potential of zinc it acts as cathode and zinc act as anode.
Cathodic reaction is Cu +2 +2e==>Cu
Anodic reaction is Zn==>Zn +2 +2e
11. What is the overall standard cell potential of a given Cu-Fe system?
a) +0.78V
b) -0.14V
c) -0.78V
d) +0.14
Answer: a
Explanation: In Cu-Fe system, copper (E 0 =+0.34V) acts as cathode and iron will acts as anode (E 0 =-0.44V). Standard cell potential of a system can be calculated using E 0 cell =E 0 cathode –E 0 anode . Therefore, overall standard cell potential of given Cu-Fe system is 0.34 – = 0.78V.
12. Which of the following metal is used as a solid interface for hydrogen gas in the standard hydrogen electrode?
a) Copper
b) Zinc
c) Gold
d) Platinized platinum
Answer: d
Explanation: Platinized platinum metal is used as the solid interface for hydrogen gas in the standard hydrogen electrode. It is due to the inertness of the metal and ease with which electron transfer occurs on its surface. Platinized platinum is black platinum-coated platinum.
Answer: a
Explanation: Nernst equation for given chemical reaction nA + mB ==> pC + qD is E=E 0 +2.3log{([A] n +[B] m )/([C] p +[D] q )} where A and B are reactants, C and D are products and m,n,p and q are the number of moles respectively.
Sanfoundry Global Education & Learning Series – Corrosion Engineering.
This set of Corrosion Engineering Objective Questions & Answers focuses on “Modern Theory Principles – Thermodynamics – 2”.
1. Which of the following is a cathode and anode respectively in the Ag-Fe system?
a) Iron and Silver
b) Silver and Iron
c) Gold and Iron
d) Iron and Gold
Answer: b
Explanation: In the Ag-Fe system, Silver acts as a cathode as the standard hydrogen potential is relatively higher than the Iron and Iron acts as anode due to relatively less standard hydrogen potential.
2. An electrochemical reaction is always a combination of oxidation half-cell and a reduction of half-cell.
a) True
b) False
Answer: a
Explanation: Corrosion is usually an electrochemical process which is a combination of oxidation half-cell and reduction half-cell. Oxidation and reduction reactions are simultaneous in nature and it is also called Redox reactions.
3. What is the cathodic and anodic reactions respectively of Cu-Ag system?
a) Ag==>Ag +2 +2e and Cu +2 +2e==>Cu
b) Cu==>Cu +2 +2e and Ag==>Ag +2 +2e
c) 2Ag +1 +2e==>2Ag and Cu==>Cu +2 +2e
d) 2Ag==>2Ag +1 +2e and Cu +2 +2e==>Cu
Answer: c
Explanation: Standard hydrogen potential of silver is +0.80V and copper is +0.34V.
Cathodic reaction: 2Ag +1 +2e==>2Ag
Anodic reaction: Cu==>Cu +2 +2e
4. Which of the following type of reaction is shown in the given figure?
a) Non-spontaneous reaction
b) Equilibrium reaction
c) Neither spontaneous nor non-spontaneous reaction
d) Spontaneous reaction
Answer: d
Explanation: Spontaneous reaction is a reaction in which the change in Gibbs free energy is negative. It means the free energy of reactants is more than the free energy of products.
5. Which of the following diagrams shows the stability of metals over a range of pH and potential of a system?
a) Phase diagrams
b) Pourbaix diagrams
c) Phase diagrams and Pourbaix diagrams
d) Colling curves
Answer: b
Explanation: Pourbaix diagrams show the stability of metal over a range of pH and potential of a system. It also includes native zone, passive zone, and corrosive zone. It is also called as potential-pH diagrams.
6. What is depicted in the given figure?
a) Phase diagram of the Fe-C system
b) Pourbaix diagram for Fe-O 2 system
c) Pourbaix diagram for Fe-H 2 O system
d) Colling curve pure iron
Answer: c
Explanation: Pourbaix diagram is a diagram that shows the stability of species of a metal over a range of pH and potential of a system. Given figures represents the pourbaix diagram of the Fe-H 2 O system.
7. Which of the following zone of given Pourbaix diagram indicates the immune zone?
a) Zone 1
b) Zone 2
c) Zone 3
d) Zone 4
Answer: a
Explanation: The Immune zone is the zone of the pourbaix diagram in which the stability of native metal in zero oxidation state is high. It is the zone in which no corrosion or passivation takes place.
8. Which of the following zone of given Pourbaix diagrams indicate a passive zone?
a) Zone 1 and 2
b) Zone 2 and 3
c) Zone 2, 3 and 6
d) Zone 4 and 5
Answer: d
Explanation: Passive zone is the zone in the pourbaix diagram in which the passivation of metal takes place. It is the operating zone in various industries to minimize corrosion and to increase the efficiency of the process.
9. Which of the following is/are the applications of Pourbaix diagrams?
a) Predicting the spontaneous direction of reactions
b) To reduce corrosion attack
c) To reduce corrosion attack, to predict the direction of spontaneous reaction and to estimate the composition of corrosion product
d) To estimate the composition of corrosion product
Answer: c
Explanation: Applications of Pourbaix diagrams:
i. Predicting the spontaneous direction of reactions
ii. To reduce corrosion attack
iii. To estimate the composition of corrosion product.
10. Which of the following is/are the limitations of Pourbaix diagrams?
a) Rate of reaction is can’t be predicted
b) It neglects the impurities of working conditions
c) Stability of metallic species is predicted
d) Rate of reaction is not predicted and it neglects the impurities of working conditions
Answer: d
Explanation: Limitations of Pourbaix diagrams:
i. Rate of reaction can’t be predicted
ii. It neglects the impurities of working conditions
iii. Alloying elements of alloys are also neglected.
This set of Corrosion Engineering Multiple Choice Questions & Answers focuses on “Modern Theory Principles – Polarization – 1”.
1. What is meant by an anode?
a) An electrode at which reduction process takes place
b) An electrode at which oxidation process takes place
c) An electrode at which neither the oxidation nor reduction takes place
d) An electrode at which both oxidation and reduction takes place
Answer: b
Explanation: An electrode at which the oxidation process takes place is known as anode whereas the electrode at which reduction process takes place is known as the cathode.
2. Which of the following is correct regarding Polarization?
a) It is the deviation from equilibrium potential
b) It results from the change in net current flow
c) Magnitude is measured in terms of overvoltage
d) It is the deviation from equilibrium potential that occurred due to the change in net current flow and its magnitude is measured in terms of overvoltage.
Answer: d
Explanation: Polarization is the deviation from equilibrium potential that occurred due to the change in net current flow and its magnitude is measured in terms of overvoltage.
3. What is the symbol of overvoltage?
a) Alpha
b) Beta
c) Eta
d) Delta
Answer: c
Explanation: The magnitude of polarization is measured in terms of over voltage and it is denoted with symbol Eta . It is the difference of corrosion potential (E corr ) and the standard potential of an electrode.
4. Exchange current density is the current per unit area of either oxidation or reduction process at the equilibrium.
a) True
b) False
Answer: a
Explanation: Exchange current density is the current per unit area of either oxidation or reduction process at the equilibrium. Type of metal and environment are the factors of exchange current density and it is denoted by i 0 .
5. What is the formula to calculate rate of oxidation or rate of reduction during equilibrium?
a) r 0 =r R =i 0 nF
b) r 0 =r R =i 0 /nF
c) r 0 =r R =i 0 n/F
d) r 0 =r R =nF/i 0
Answer: b
Explanation: Equilibrium is defined as the state at which rate of oxidation is equal to the rate of reduction. And the formula to calculate rate of oxidation or reduction is r 0 =r R =i 0 /nF where i 0 is exchange current density, n is number of electrons involved and F is faraday’s constant.
6. Which of the following metal shows the highest exchange current density for hydrogen-hydrogen ion as per given figure?
a) Mercury
b) Iron
c) Platinized platinum
d) Platinum
Answer: c
Explanation: Platinized platinum shows the highest exchange current density for hydrogen-hydrogen ion due to its high inertness and electrically conductivity. The order follows as (i 0 ) Pt H+/H2 >(i 0 ) Fe H+/H2 >(i 0 ) Hg H+/H2 .
7. Which of the following is the controlling factor of Activation polarization?
a) The activation energy of a reaction
b) Diffusion of ions in the solution
c) The temperature of a solution
d) The velocity of a solution
Answer: a
Explanation: Activation polarization is the mechanism of polarization that depends on the activation energy of a reaction. Activation energy is the minimum energy required for reacting species to undergo chemical reactions.
8. Which of the following mentioned is/are the types of polarization?
a) Activation polarization
b) Concentration polarization
c) Resistance polarization
d) Activation, concentration and resistance polarization
Answer: d
Explanation: Types of polarization:
Activation polarization
Concentration polarization
Resistance polarization.
9. What is the relationship between reaction rate and overvoltage for activation polarization?
a) n a =±Î˛log(i 0 /i)
b) n a =±Î˛log(I/i 0 )
c) n a =±Î˛log(1-i 0 /i)
d) n a =±Î˛log(1-i/i 0 )
Answer: b
Explanation: The relationship between reaction rate and overvoltage for activation polarization can be noted as n a =±Î˛log(I/i 0 ) where β is a Tafel constant and i 0 is exchange current density.
10. What is depicted in the given figure?
a) Concentration polarization of hydrogen-hydrogen ion
b) Resistance polarization of hydrogen-hydrogen ion
c) Activation polarization of hydrogen-hydrogen ion
d) Both activation and concentration polarization of hydrogen-hydrogen ion
Answer: c
Explanation: The given figure depicts the activation polarization of the hydrogen-hydrogen ion electrode. Curve1 indicates the cathodic polarization whereas curve2 indicates the anodic polarization.
This set of Corrosion Engineering Questions & Answers for Exams focuses on “Modern Theory Principles – Polarization – 2”.
1. Which of the following is/are correct regarding concentration polarization?
a) Diffusion of ions in the bulk solution is the controlling factor
b) It usually operates at a high current density
c) It is a continuation of Activation polarization
d) It is a continuation of activation polarization, diffusion of ions in the bulk solution is the controlling factor and it usually operates at high current densities
Answer: d
Explanation: Concentration polarization is the mechanism of polarization in which diffusion of ions in the bulk solution is the controlling factor, it is a continuation of activation polarization and it usually operates at high current densities.
2. What is depicted in the given figure?
a) Activation polarization
b) Concentration polarization
c) Resistance polarization
d) Activation and concentration polarization
Answer: b
Explanation: The given figure depicts the concentration polarization of a reaction. It is the mechanism of polarization in which the diffusion of ions in the bulk solution is the controlling factor. It usually encounters at high-density currents and low concentration solution.
3. What is the formula to determine limiting diffusion current density (i L ) of concentration polarization?
a) i L =xnFC B /D
b) i L =DC B /nFx
c) i L =DnFC B /x
d) i L =x/DnFC B
Answer: c
Explanation: i L =DnFC B /x is the formula to determine the limiting diffusion current density (i L ) of concentration polarization. Where I L is the limiting diffusion current density, D is the diffusion coefficient, C B concentration of ions in bulk solution and x is the thickness of diffusion layer.
4. Agitation will increase the limiting diffusion current density of concentration polarization.
a) True
b) False
Answer: a
Explanation: Agitation tends to decrease the thickness of the diffusion layer by supply enough ions to the metal interface hence there will be an increase in limiting diffusion current density of concentration polarization.
5. Which of the following is/are correct regarding the given figure?
a) Velocity, temperature, and concentration are the factors that influence limiting current density
b) Limiting current density decreases with an increase in velocity, temperature, and concentration
c) Limiting current density increase with the increase in velocity, temperature, and concentration
d) Velocity, temperature, and concentration are the factors that influence limiting current density and it increases as it increases
Answer: d
Explanation: The given figure shows the increase in limiting diffusion current density of concentration polarization with an increase in velocity, temperature, or concentration. It is due to the relatively high availability of reacting species at the interface and decrease in thickness of the diffusion layer.
6. Which of the following type of polarization is depicted in the given figure?
a) Activation polarization
b) Concentration polarization
c) Activation and concentration polarization
d) Resistance polarization
Answer: c
Explanation: The given figure depicts the cathodic polarization of an element with activation and concentration polarizations. Concentration polarization is the continuation of activation polarization at higher current densities.
7. Which of the following is/are correct regarding resistance polarization?
a) Activation energy at the interface is the controlling factor
b) The resistance of transition between electrodes and electrolytes
c) Diffusion of ions in the bulk solution is the controlling factor
d) The resistance of reacting ions for diffusion is the controlling factor
Answer: b
Explanation: Resistance polarization is the type of polarization in which there is a resistance of transition between electrodes and electrolytes. But this polarization has a negligible effect on corrosion kinetics.
8. Which two scientists present the first formal presentation on mixed potential theory?
a) Wagner and Traud
b) Wagner and Evans
c) Traud and Nernst
d) Wilsmore and Nernst
Answer: d
Explanation: Mixed potential theory is the electrochemical hypothesis of modern corrosion presented by Wagner and Traud in the year 1938. It relates the potentials and currents of the corrosion system to determine corrosion potential (E corr ) and corrosion current (i corr ).
9. Which of the following is/are the hypothesis of mixed potential theory?
a) Any electrochemical reaction can be divided into two or more partial reactions
b) No net accumulation of electric charge during the reaction
c) Any electrochemical reaction can be divided into two or more partial reactions and no net accumulation of electric charge during the reaction
d) Electrochemical reactions can’t be divided into partial reactions
Answer: c
Explanation: Hypothesis of mixed potential theory:
i. Any electrochemical reactions can be divided into two or more partial reactions
ii. No net accumulation of electric charge during the reaction.
10. Which of the following is depicted in the given mixed potential schematic?
a) Dissolution of zinc
b) Oxidation of hydrogen
c) Reduction of zinc
d) Dissolution of copper
Answer: a
Explanation: The given mixed potential schematic depicts the dissolution of zinc. It shows the anodic polarization of zinc, cathodic polarization of hydrogen, and resulting in E corr and i corr .
This set of Corrosion Engineering Multiple Choice Questions & Answers focuses on “Modern Theory Principles – Passivity”.
1. Which of the following is/are correct regarding passivation?
a) It is defined as the loss of reactivity at certain conditions
b) Usually results in the formation of the oxide layer
c) The corrosion rates are relatively low
d) It is defined as loss of reactivity at certain conditions usually due to the formation of the oxide layer and corrosion rates are relatively low
Answer: d
Explanation: Passivation is defined as the loss of reactivity of metals/alloys at certain conditions usually due to the formation of the oxide layer and corrosion rates are relatively low.
2. The passive state of a metal is often relatively unstable and subject to damage.
a) True
b) False
Answer: a
Explanation: Passivation is the loss of chemical reactivity of a metal due to the formation of the oxide layer. It is relatively unstable and subject to damage. Chemical properties, wear resistance and thickness are the factors for the stability of the passive layer.
3. Which of the following is/are the metal/alloys that demonstrate active-passive transitions?
a) Iron and stainless steels
b) Nickel and its alloys
c) Iron, stainless steels, nickels, titanium, and its alloys
d) Titanium and its alloys
Answer: c
Explanation: Metals/alloys that demonstrate active-passive transitions is/are:
Iron and stainless steels
Nickel and its alloys
Titanium and its alloys
Chromium
Aluminum and its alloys.
4. What is depicted in the given polarization curve?
a) Cathodic dissolution of typical active-passive transition metal
b) Anodic dissolution of typical active-passive transition metal
c) Anodic dissolution of a metal
d) Cathodic dissolution of a metal
Answer: b
Explanation: Given the polarization curve, depicts the typical anodic dissolution of active-passive transition metal. It includes an active region, passive region, and trans passive region.
5. Which of the following is/are correct regarding the active region of metals?
a) Corrosion rates increase exponentially
b) Corrosion rates increase linearly
c) It follows typical Tafel behavior
d) It follows typical Tafel behavior and corrosion rates increases exponentially
Answer: d
Explanation: Active region is the first stage of active-passive transition in which the corrosion rates increase exponentially and it follows typical Tafel behavior.
6. The Trans passive region is the region in which the corrosion rate increases with an increase in potential.
a) True
b) False
Answer: a
Explanation: Trans passive region is the last region of active-passive transitions of metal in which the corrosion rate increases with an increase in potential. It is formed due to the instability of the passive layer at that high potentials.
7. Which of the following is/are the important characteristics of active-passive transitions of a metal?
a) Passive potential (E pp )
b) Critical anodic current density (i c )
c) Passive potential (E pp ) and Critical anodic current density (i c )
d) Neither passive potential nor critical anodic current density
Answer: c
Explanation: Passive potential is defined as the potential of a system at which the passivation of metal is starts whereas critical anodic current density is defined as the current density at which passivation of metals starts.
8. Which of the following statements is/are correct regarding the given schematic?
a) Increase in acid concentration and temperature increase the passive potential
b) Increase in acid concentration and temperature increase critical current density
c) The relative reduction in the size of the passive region
d) Increase in acid concentration and temperature increase critical current density, passive potential and we can observe a relative reduction in the size of the passive region
Answer: d
Explanation: Statements that are correct regarding the given schematic are:
Increase in acid concentration and temperature increase the passive potential
Increase in acid concentration and temperature increase critical current density
The relative reduction in the size of the passive region.
9. Which of the following metal doesn’t possess a trans passive region?
a) Iron
b) Titanium
c) Nickel
d) Aluminum
Answer: b
Explanation: Typical active-passive transitions metals possess active region, passive region, and trans passive region. Whereas titanium doesn’t possess trans passive region is due to the formation of a more protective titanium oxide film structure.
10. Which of the following metals/alloys passivates spontaneously in acid solutions containing oxidizers or dissolved oxygen?
a) Copper
b) Titanium
c) Stainless steels and titanium
d) Nickel
Answer: b
Explanation: Stainless steels and titanium passivates spontaneously in acid solutions containing oxidizers or dissolved oxygen. A decrease in passive potential and critical current density is the driving force for the spontaneous passivation.
This set of Corrosion Engineering Questions and Answers for Aptitude test focuses on “Modern Theory Applications – Predicting Corrosion Behavior”.
1. Which of the following is/are the applications of mixed-potential theory?
a) Permit prediction of complex corrosion behavior
b) To develop new corrosion prevention methods
c) To develop new rapid corrosion rate measurement
d) Permit prediction of complex corrosion behavior, to develop new corrosion prevention methods and to develop new rapid corrosion rate measurement
Answer: d
Explanation: Applications of the mixed-potential theory are:
Permit prediction of complex corrosion behavior
To develop new corrosion prevention methods
To develop new rapid corrosion rate measurement.
2. Which of the following is/are correct when oxidizing agents are added to a corrosion system containing a non-passivating metal?
a) Rate of corrosion decreases after certain potential
b) Rate of corrosion increases with increase in oxidizers concentration
c) Rate of corrosion increases after certain potential
d) Results in the formation stable oxide layer
Answer: b
Explanation: The rate of corrosion increases with increase as the concentration of oxidizing agents containing non-passivating metal. It is due to the reduction of oxygen on the surface of the metal and due to the absence of an oxide layer.
3. Which of the following is described in the given figure?
a) Effect of oxidizers concentration on cathodic behavior of active metal
b) Effect of oxidizers concentration on the electrochemical behavior of active metal
c) Effect of oxidizers concentration on the electrochemical behavior of active-passive transition metal
d) Effect of oxidizers concentration on cathodic behavior of active-passive transition metal
Answer: c
Explanation: The given figure describes the effect of oxidizers concentration on the electrochemical behavior of active-passive transition metal. The rate of oxygen reduction varies with oxidizer concentration and the corresponding rate of metallic dissolution varies.
4. What is the potential of oxidizers at which metal passivation starts according to a given figure?
a) Concentration corresponding to C
b) Concentration corresponding to D
c) Concentration corresponding to A
d) Concentration corresponding to B
Answer: a
Explanation: Given the figure describes the effect of oxidizer concentration on the electrochemical behavior of active-passive transition metal. Passivation of metal starts at the oxidizer’s concentration corresponding to point C.
5. Which of the following is described in the given figure?
a) Effect of velocity on anodic dissolution of oxygen
b) Effect of velocity on the electrochemical behavior of active-passive transition metal
c) Effect of velocity on the electrochemical behavior of a normal metal
d) Effect of velocity on the cathodic dissolution of metal
Answer: c
Explanation: The given figure depicts the effect of velocity on the electrochemical behavior of a normal metal. Here metallic dissolution is anodic reaction and reduction of oxygen is a cathodic reaction.
6. The corrosion rate is usually dependent at low velocity whereas at high velocities it becomes independent.
a) True
b) False
Answer: a
Explanation: Corrosion rate is usually dependent at low velocities whereas at high velocities it becomes independent. It is due to enough availability of ions at the interface and thereby it depends on activation energy.
7. Which of the following type of polarization has a negligible effect on velocity?
a) Concentration polarization
b) Activation polarization
c) Concentration polarization and Activation polarization
d) Neither concentration nor Activation polarization
Answer: b
Explanation: Activation polarization is the mechanism of polarization in which the activation energy of reactants at the interface is the driving force. It has a negligible effect on velocity as it is independent of diffusion of ions in the bulk solution.
8. Which of the following is depicted in the given figure?
a) Galvanic effect of copper-platinum
b) Corrosion of platinum
c) Corrosion of Zinc
d) Galvanic effect of zinc-platinum
Answer: d
Explanation: The given figure depicts the galvanic effect of zinc-platinum. Corrosion of zinc increases preferentially as the total rate of hydrogen evolution increases on zinc and platinum.
9. Severe corrosion of metals occurred when coupled with platinum is due to the higher current density for hydrogen evolution but not due to the reversible potential of the platinum-platinum ion electrode.
a) True
b) False
Answer: a
Explanation: Severe corrosion of metals occurred when coupled with platinum is due to the higher current density for evolution but not due to the reversible potential of the platinum-platinum ion electrode. Notably, platinized platinum has the highest exchange current density for hydrogen evolution.
10. The reversible potential of gold is more positive than platinum in emf series whereas in galvanic series the position of gold is below platinum.
a) False
b) True
Answer: b
Explanation: The reversible potential of gold is more positive than platinum in emf series whereas in galvanic series the position of gold is below platinum. It is due to the exchange current density of hydrogen evolution, as the galvanic tests are usually conducted in an acidic environment.
11. Which of the following is depicted in the given figure?
a) Galvanic effect of the zinc-platinum couple
b) Effect of the velocity of zinc-platinum couple
c) Effect of the cathode-anode area ratio of a zinc-platinum couple
d) Effect of oxidizers on the zinc-platinum couple
Answer: c
Explanation: The given figure depicts the effect of the cathode-anode area ratio of the zinc-platinum couple. The exchange current density of hydrogen evolution on platinum (10cm 2 ) is more than the current density of platinum (1cm 2 ).
12. In a galvanic couple, the corrosion rate of the metal with active corrosion potential is accelerated whereas the corrosion rate of noble metal retards preferentially.
a) True
b) False
Answer: a
Explanation: In a galvanic couple, one metal acts as the anode , and its corrosion rate is accelerated whereas other acts as the cathode and its corrosion rate are retards preferentially.
13. Which of the following metals that are spontaneously passivated on coupling with platinum?
a) Titanium
b) Chromium
c) Titanium and Chromium
d) Neither titanium nor chromium
Answer: c
Explanation: Titanium and chromium metals are the metals that are spontaneously passivated on coupling with platinum. It is due to the mixed potential of galvanic couples lies in the protection region of the passive region.
14. Which of the following is/are correct regarding the potentiostat method?
a) It is a polarization technique that allows for controlled polarization
b) It works on controlling voltage between a working and reference electrode
c) It is a corrosion analysis method
d) It is a corrosion analysis technique method that allows for controlled polarization and it works on controlling voltage between a working and reference electrode.
Answer: d
Explanation: It is a corrosion analysis technique method that allows for controlled polarization and it works in controlling voltage between a working and reference electrode.
This set of Corrosion Engineering online quiz focuses on “Modern Theory Applications – Corrosion Rate Measurement”.
1. What is meant by anodic protection?
a) Accompanying the sacrificial metal with metallic structure
b) Prevention of corrosion by impressed cathodic current by supply electrons
c) Prevention of corrosion by the impressed anodic current is used to transform from active to a passive state
d) Additions of oxidizers and oxidizing agents for the formation of an oxide layer
Answer: c
Explanation: Anodic protection is one of the corrosion prevention or protection method in which the impressed anodic current is used to transform from active to a passive state.
2. The optimum potential for anodic protection is in the mid of passive region since it permits slight variations.
a) True
b) False
Answer: a
Explanation: Anodic protection is a corrosion prevention method in which anodic current of certain potential is provided to the metallic structure to transform from active to a passive state. The optimum potential for anodic protection is in the mid of passive region since it permits slight variations.
3. Which of the following is described in the given figure?
a) Protection range for anodic protection for an active metal
b) Protection range for anodic protection for an active-passive transition metal
c) Protection range for cathodic protection for an active-passive transition metal
d) Protection range for cathodic protection for an active metal
Answer: b
Explanation: The given figure depicts the anodic protection range for an active-passive transition metal. The optimum potential is usually at the mid-portion of a passive region of metal to permits slight variations.
4. Which of the following noble metals will improve the corrosion resistance of titanium and chromium on galvanic coupling?
a) Platinum
b) Palladium
c) Rhodium
d) Platinum, palladium, and rhodium
Answer: d
Explanation: Noble metals such as platinum, palladium, and rhodium on galvanic coupling will improve the corrosion resistance of titanium and chromium by spontaneous passivation. It is due to the mixed potential of the couple lies in the passive region of titanium and chromium.
5. Stainless steels containing small quantities of platinum passivates more readily in the presence of oxygen, ferric salts, and other oxidizing agents.
a) False
b) True
Answer: b
Explanation: Stainless steels containing small quantities of platinum passivates more readily in the presence of oxygen, ferric salts, and other oxidizing agents. It is due to the resultant mixed potential of an alloy that reaches a passive region quickly.
6. Which of the following electrochemical methods is/are used to determine the corrosion rate?
a) Tafel extrapolation
b) Linear polarization
c) Tafel extrapolation and linear polarization
d) Neither Tafel extrapolation nor linear polarization
Answer: c
Explanation: Tafel extrapolation and linear polarization are the two electrochemical methods used to determine the corrosion rate. These methods are extensively used for laboratory and industrial corrosion tests.
7. Which of the following is depicted in the given figure?
a) Electric circuit for cathodic polarization measurements
b) Electric circuit for anodic polarization measurements
c) Electric circuit for cathodic protection
d) Electric circuit for sacrificial anode system
Answer: a
Explanation: The given figure depicts the electric circuit for cathodic polarization measurements. This cathodic polarization is preferred over anodic polarization is due to the ease to measure experimentally.
8. The applied current cathodic polarization curve of a corroding metal is non-linear at low currents, but it becomes linear at higher currents on a semilogarithmic plot.
a) False
b) True
Answer: b
Explanation: The cathodic polarization curve is the curve drawn by measuring over voltage between reference and the working electrode on a semilogarithmic plot. It is non-linear at low currents whereas it becomes linear at higher currents.
9. Which of the following is depicted in the given figure?
a) Linear polarization curve
b) Mixed potential curve
c) Anodic polarization curve
d) Cathodic polarization curve
Answer: d
Explanation: The given depicts the cathodic polarization curve. Applied cathodic currents are equal to the difference between the current corresponding to the reduction process and that of the oxidation process. It is used to know the corrosion of metals.
10. Which of the following is/are the advantages of Tafel extrapolation?
a) It can measure extremely low corrosion rates
b) It can be used for continuously monitoring the corrosion rate of a system
c) It can be used for continuously monitoring the corrosion rate of a system with high accuracy and measures extremely low corrosion rates
d) It can be performed rapidly with high accuracy
Answer: c
Explanation: Advantages of Tafel extrapolation are:
It can measure extremely low corrosion rates
It can be used for continuously monitoring the corrosion rate of a system
It can be performed rapidly with high accuracy.
11. Which of the following is/are the limitations of Tafel extrapolation?
a) For reasonable accuracy, the Tafel region must be extended
b) It can be applied to systems containing one reduction process only
c) Much interference from concentration polarization
d) It can be applied to systems containing one reduction process, for reasonable accuracy the Tafel region must be extended and there will be much interference from concentration polarization
Answer: d
Explanation: Limitations of Tafel extrapolation are:
For reasonable accuracy, the Tafel region must be extended
It can be applied to systems containing one reduction process only
Much interference from concentration polarization.
12. What is the range of current density around corrosion potential that will observe that the applied current density is a linear function of the electrode potential?
a) 10 mV more noble or active around corrosion potential
b) 5 mV more noble or active around corrosion potential
c) 10 V more noble or active around corrosion potential
d) 5 V more noble or active around corrosion potential
Answer: a
Explanation: In around 10 millivolts around corrosion potential, it is observed that the applied current density is a linear function of the electrode potential. It is known as a linear polarization curve.
13. What is the formula to determine the slope of linear polarization curve?
a) ΔE/Δi =[2.3*icorr*]/[βa*βb]
b) ΔE/Δi=[βa+βb]/[2.3*icorr*]
c) ΔE/Δi=[βa*βb]/[2.3*icorr*]
d) ΔE/Δi=[2.3*icorr*]/[βa+βb]
Answer: c
Explanation: The slope of linear polarization curve is determined by using ΔE/Δi=[βa*βb]/[2.3*icorr*] where βa , βb are Tafel slopes of anodic and cathodic reactions and icorr is the current density at the intersection point of anodic and cathodic reaction.
14. Which of the following is depicted in the given figure?
a) Anodic polarization curve
b) Linear-polarization curve
c) Cathodic polarization curve
d) Mixed potential curve
Answer: b
Explanation: Linear polarization curve is drawn in around 10 millivolts around noble and 10 millivolts active around corrosion potential. It is used to determine the corrosion rate in industries and laboratory techniques by using formula ΔE/Δi = [βa*βb] / [2.3*icorr*].
15. Which of the following industries uses Tafel extrapolation or linear polarization to measure low corrosion rates?
a) Nuclear industries
b) Pharmaceutical industries
c) Food processing industries
d) Nuclear, pharmaceutical and food processing industries
Answer: d
Explanation: Nuclear, pharmaceutical, and food processing industries are the industries that use Tafel extrapolation or linear polarization where measuring low corrosion rates is important. Traces of impurities or contamination in these industries could lead to catastrophic failure.
This set of Corrosion Engineering Multiple Choice Questions & Answers focuses on “High-Temperature Corrosion – 1”.
1. Which of the following is/are the systems that are prone to high-temperature corrosion?
a) Gas turbines
b) Rocket engines
c) Furnaces
d) Gas turbines, rocket engines, and furnaces
Answer: d
Explanation: High-temperature systems such as gas turbines, rocket engines, and furnaces are prone to high-temperature corrosion due to high working temperature and petrochemical corrosive atmosphere around it.
2. Pilling and Bed worth proposed that oxidation resistance is related to the volume ratio of oxide and metal per grams atom of metal.
a) True
b) False
Answer: a
Explanation: Pilling and Bed worth proposed that oxidation resistance of a metal oxide is related to the volume ratio of oxide and metal per grams atom of metal.
3. Which of the following is/are the characteristics of a metal oxide if the Pilling and Bed worth ratio is less than 1?
a) Protective
b) Unprotective
c) Unprotective and insufficient oxide
d) Unprotective and sufficient oxide
Answer: c
Explanation: If Pilling and Bed worth ratio of a metal oxide is less than 1 then it is an unprotective and insufficient oxide, if it is near to 1 then it is protective and adherent and if it is greater than 1 then it is unprotective.
4. Which of the following is/are the causes for the poor oxidation resistance of metal oxide with high Pilling and Bed worth ratio?
a) Large compressive stresses in the oxide
b) Cracking
c) Spalling
d) Large compressive stresses in the oxide, cracking and spalling
Answer: d
Explanation: Metal oxides with a value greater than 1 Pilling and Bed worth ratio have poor oxidation resistance due to large compressive stresses in the oxide, cracking, and spalling.
5. Which of the following is/are the ideal characteristics of the passive metal oxide layer?
a) Good adherence and high melting point
b) Low electrical conductivity and low vapor pressure
c) Good adherence, high melting point, low vapor pressure, and low electrical conductivity
d) Good adherence and high vapor pressure
Answer: c
Explanation: Ideal characteristics of passive metal oxides layer are:
Good adherence
High melting point
Low electrical conductivity
Low vapor pressure
Low diffusion coefficient.
6. Which of the following metal has a nonprotective oxide?
a) Cadmium (CdO 2 )
b) Copper (Cu 2 O)
c) Chromium (Cr 2 O 3 )
d) Silicon (SiO 2 )
Answer: a
Explanation: Metal oxides can be categorized into protective and nonprotective based on the value of the Pilling and Bed worth ratio. Here, copper , chromium , and silicon are protective in nature whereas oxide of cadmium is unprotective.
7. What is the value of the Pilling and Bed worth ratio of tungsten?
a) 1.21
b) 3.40
c) 2.60
d) 0.45
Answer: b
Explanation: Pilling and Bed worth ratio is defined as the volume ratio of oxide and metal per grams atom of metal. The Pilling and Bed worth ratio of tungsten is around 3.40 and it is unprotective in nature.
8. Which of the following is/are the interface at which new metallic oxides are produced?
a) Metal-scale interface
b) Scale-gas interface
c) Metal-scale interface or scale-gas interface
d) Neither metal-scale interface nor scale-gas interface
Answer: c
Explanation: New metallic oxides is produced at a metal-gas interface or scale-gas interface based on the diffusion coefficient of metallic and oxygen ions in the metal matrix.
9. The diffusion of either cation or oxygen ions usually controls the reaction rate of high-temperature metallic oxidation.
a) True
b) False
Answer: a
Explanation: High-temperature metal-oxygen interaction can’t be separated electrically whereas diffusion of either cation or oxygen ions usually controls the reaction rate of high-temperature metallic oxidation.
10. Which of the following is depicted in the given figure?
a) Metal-liquid oxidation
b) Metal-gas oxidation
c) Metal-metal oxidation
d) Aqueous metal corrosion
Answer: b
Explanation: The given figure depicts the metal-gas oxidation and it also depicted the electrochemical process occurring during gaseous oxidation. It includes metal, metal oxide, and an oxygen atmosphere.
11. Which of the following order is correct regarding the oxides of iron starting from metallic iron to gaseous oxygen interface?
a) FeO, Fe 2 O 3 , and Fe 3 O 4
b) Fe 2 O 3 , Fe 3 O 4 and FeO
c) Fe 3 O 4 , Fe 2 O 3 , and FeO
d) FeO, Fe 3 O 4 , and Fe 2 O 3
Answer: d
Explanation: The most oxygen-rich compound is found at the scale-gas interface whereas a metal-rich compound is found at the metal-scale interface. Therefore, the correct order is FeO(22.270% O 2 ), Fe 3 O 4 (27.641% O 2 ), and Fe 3 O 4 (30.057% O 2 ).
12. The relative thickness of each phase of a metallic oxide is determined by the rate of ionic diffusion through that phase.
a) True
b) False
Answer: a
Explanation: The relative thickness of each phase of a metallic oxide is determined by the rate of ionic diffusion through that phase. Diffusion of ions may include metallic ions such as Fe +2 or Fe +3 or oxygen ions.
13. Which of the following metal produces metal oxide at a metal-scale interface?
a) Titanium
b) Niobium
c) Zirconium
d) Titanium, Niobium, and Zirconium
Answer: d
Explanation: Titanium, Niobium, Zirconium, Hafnium, and Tantalum are the metals that produce metal oxides at the metal-scale interface. It is due to the predominant diffusion of oxygen-ion rather than metallic cation.
14. Which of the following is/are the n-type semiconducting oxides?
a) CdO 2
b) TiO 2
c) Al 2 O 3 , CdO 2 , and TiO 2
d) CoO
Answer: c
Explanation: Semiconducting oxides such as CdO 2 , Al 2 O 3 , CdO, TiO 2 , Ta 2 O 5 , and SiO 2 are n-type semiconductors. It contains an excess of negatively charged electronic current carriers I.e. electrons.
Answer: b
Explanation: Semiconducting oxides such as FeO, MnO, Cu 2 O, and CoO are the p-type semiconducting oxides whereas Al 2 O 3 , CdO 2 are n-type oxides. In this, ionic transport occurs by metallic vacancies.
Sanfoundry Global Education & Learning Series – Corrosion Engineering.
This set of Corrosion Engineering online test focuses on “High-Temperature Corrosion – 2”.
1. In general, all oxides are nonstoichiometric in nature their composition varies from an ideal molecular formula.
a) True
b) False
Answer: a
Explanation: In general, all oxides are nonstoichiometric in nature their compositions vary from an ideal molecular formula. It is due to the excess or deficiency in metallic ions or equivalent oxygen ions.
2. Which of the following is/are correct regarding the measurement of the rate of oxidation?
a) Weight loss per unit area of metal is the measure of the rate of oxidation
b) Either weight loss or weight gain per unit area of metal is the measure of the rate of oxidation
c) Weight gain per unit area of metal is the measure of the rate of oxidation
d) Neither weight loss nor weight gain per unit area of metals is the measure of the rate of oxidation
Answer: c
Explanation: Rate of oxidation is usually measured and expressed in terms of weight gain per unit area of metal. As oxidation results in the conversion from metal M to metallic oxides MOn .
3. Diffusion-controlled oxidation can be minimized by decreasing the concentration of ionic defects in the scale.
a) False
b) True
Answer: b
Explanation: diffusion-controlled oxidation can be minimized by decreasing the concentration of ionic defects in the scale. These defects include Frenkel defect, Schottky defect, and many crystallographic defects.
4. What are the types of oxidation rate laws?
a) Linear and parabolic law
b) Cubic and logarithmic law
c) Linear, parabolic and cubic law
d) Linear, parabolic, cubic and logarithmic law
Answer: d
Explanation: Oxidation rate laws are classified based on the variation of oxidation rate in different metals. They are linear, parabolic, cubic, and logarithmic laws.
5. Which of the following oxidation rate law is depicted as x in the given figure?
a) Linear law
b) Parabolic law
c) Cubic law
d) Parabolic law
Answer: a
Explanation: The given figure depicts the graphical representation of oxidation laws. Linear oxidation law is denoted by letter x. Linear law states that weight gain per unit metal is directly proportional to the time of exposure.
6. Which of the following oxidation rate law is depicted as z in the given figure?
a) Linear law
b) Parabolic law
c) Cubic law
d) Parabolic law
Answer: c
Explanation: The given figure depicts the graphical representation of oxidation laws. Cubic law is denoted as letter z and it states that cube of weight gain per unit metal is directly proportional to the time of exposure.
7. Which of the following is/are correct regarding linear oxidation law?
a) Weight gain per unit area of the metal is directly proportional to the exposure time
b) It is a characteristic of porous or cracked scale
c) Sodium is an example that follows linear oxidation law
d) Weight gain per unit area of metal is directly proportional to exposure time, it is characteristic of porous or cracked scale and sodium follows linear oxidation law
Answer: d
Explanation: Linear oxidation law:
Weight gain per unit area of the metal is directly proportional to the exposure time
It is characteristics of porous or cracked scale
Sodium follows linear oxidation law.
8. Which of the following metal doesn’t follow linear oxidation law?
a) Sodium
b) Aluminum
c) Niobium
d) Potassium
Answer: b
Explanation: Linear oxidation law states that an increase in weight per unit area of metal is directly proportional to the time of exposure. Metals such as sodium, potassium, tantalum, and niobium follow linear oxidation law whereas aluminum follows the logarithmic oxidation law.
9. Which of the following is/are true regarding parabolic oxidation rate law?
a) It was proposed by C. Wagner
b) It states that square of weight loss is directly proportional to the time of exposure
c) It was proposed by C. Wagner which states that square of weight loss is directly proportional to the time of exposure and it resembles non-steady-state diffusion-controlled reactions
d) It resembles non-steady-state diffusion-controlled reactions
Answer: c
Explanation: True statements regarding parabolic oxidation rate law:
It was proposed by C. Wagner
It states that square of weight loss is directly proportional to the time of exposure
It resembles non-steady-state diffusion-controlled reactions.
Answer: d
Explanation: Logarithmic law is observed in thin sections of oxide layers at low temperatures. Metals such as aluminum, copper, iron, and other metals follow logarithmic oxidation rate law.
Sanfoundry Global Education & Learning Series – Corrosion Engineering.
This set of Corrosion Engineering Multiple Choice Questions & Answers focuses on “High Temperature Materials”.
1. Metals that follow linear oxidation kinetics at low temperatures tend to oxidize catastrophicallyat high temperatures.
a) True
b) False
Answer: a
Explanation: Metals that follows linear oxidation kinetics at low temperature tend to oxidize catastrophically at high temperatures. It is due to the rapid exothermic reactions at the surfaces at high temperatures.
2. Which of the following metals results in the ignition in extreme cases?
a) Sodium
b) Magnesium
c) Niobium
d) Sodium, magnesium, and niobium
Answer: d
Explanation: If the rate of heat transfer from metal to surroundings is less than heat evolution from oxide formation then it increases the surface temperature of metals. This leads to the ignition of metals and it includes sodium, magnesium, and niobium.
3. Which of the following metals results in the formation of volatile oxides?
a) Molybdenum
b) Tungsten
c) Osmium, tungsten, molybdenum, and Vanadium
d) Vanadium
Answer: c
Explanation: Volatile oxides are the oxides that get evaporate within the fractions of seconds after their formation. Metals that form volatile oxides include osmium, tungsten, molybdenum, and vanadium.
4. Which of the following is/are true regarding internal corrosion?
a) Corrosion products precipitate in the metal matrix
b) Corrosion products precipitate in the metal matrix and metals such as Fe, Ni, and Co are highly prone to internal corrosion
c) Corrosion occurs on external surfaces of metals
d) It is due to the stable corrosion products of base metals
Answer: b
Explanation: Internal corrosion is due to the one or more dilute alloying elements form more stable oxides than the base metal and preferentially forms corrosion in the metal matrix. Iron, nickel, and cobalt are the base metals that are prone to internal corrosion.
5. Dilute alloying elements of base metals exhibiting a relatively high solubility and diffusivity for atomic oxygen are subject to internal corrosion.
a) True
b) False
Answer: a
Explanation: Dilute alloying elements of base metals exhibiting a relatively high solubility and diffusivity for atomic oxygen are subject to internal corrosion. It is due to the formation of preferential stable oxides than the base metals.
6. Which of the following mechanical properties is/are important in structural applications of metals?
a) Tensile strength
b) Yield strength
c) Ductility and Elasticity
d) Tensile strength, Yield strength, Ductility, and Fracture toughness
Answer: d
Explanation: Mechanical properties that are important in structural applications of metals are:
i. Tensile strength
ii. Yield strength
iii. Ductility
iv. Fracture toughness.
7. Which of the following is/are correct regarding creep?
a) It is the continuous plastic elongation of metal under constant load
b) It is the high-temperature mechanical effect of a metal
c) It is the continuous plastic elongation of metal under constant load at high temperature and it can be minimized by the fraction of grain boundaries
d) It can be minimized by reducing the fraction of grain boundaries
Answer: c
Explanation: It is defined as the continuous plastic elongation of metal under constant load at high temperatures. Creep rate is then expressed as percent elongation in a given time. It can be minimized by reducing the fraction of grain boundaries.
8. Which of the following is/are true regarding stress rupture?
a) The stress required to cause a rupture in a predetermined time at a constant temperature
b) It is important in short-term high-temperature applications
c) Stress rupture is an important mechanical property for gas turbine or rocket engines
d) The stress required to cause a rupture in short-term high-temperature applications at a predetermined time is known as stress rupture and it is an important mechanical property for gas turbines and rocket engines
Answer: d
Explanation: Stress rupture is defined as the amount of stress that is required to cause a rupture in short-term high-temperature applications at a predetermined time. It is an important mechanical property for gas turbines and rocket engines.
9. Which of the following is/are the adequate high-temperature mechanical properties to avoid fracture?
a) Low creep rate and high stress-rupture strength
b) High stress-rupture strength, low creep rate, and high fracture toughness
c) High stress-rupture strength and high fracture toughness
d) Low creep rate and high fracture toughness
Answer: b
Explanation: Low creep rate, high stress-rupture strength, and high fracture toughness are the adequate high-temperature mechanical properties to avoid fracture.
10. Which of the following strengthening mechanisms is/are used to attain high-temperature strength?
a) Solid-solution strengthening
b) Precipitation hardening
c) Dispersion hardening
d) Solid-solution strengthening, precipitation hardening or dispersion hardening
Answer: d
Explanation: Strengthening mechanism that is used to attain high-temperature strength are:
i. Solid-solution strengthening
ii. Precipitation hardening
iii. Dispersion hardening.
11. Which of the following metallurgical changes that affect the structural stability of metals at high temperatures?
a) Grain growth, phase changes, precipitation dissolution and precipitation over aging
b) Grain growth and phase changes
c) Precipitation dissolution and precipitation over aging
d) Phase changes, precipitation dissolution and precipitation over aging
Answer: a
Explanation: Metallurgical changes that affect the structural stability of metals at high temperature are:
i. Grain growth
ii. Phase changes
iii. Precipitation dissolution
iv. Precipitation over aging.
12. Which of the following nickel-based alloys is/are superalloys?
a) Hastelloy C-276
b) Inconel 718
c) Hastelloy C-276, Inconel 718 and Hastelloy HX
d) Hastelloy HX
Answer: c
Explanation: Superalloys or high-performance alloys are the alloys that can resist extreme conditions such as high temperature, high stress, high wear, and corrosive atmospheres. Nickel-based alloys are widely used as superalloys that include Hastelloy C-276, Inconel 718, and Hastelloy HX.
13. Which of the following is/are the high melting point metals?
a) Molybdenum
b) Tungsten
c) Columbium
d) Molybdenum, tungsten, columbium, and tantalum
Answer: d
Explanation: Metals – Melting points
i. Tungsten – 6170°F
ii. Tantalum – 5430°F
iii. Molybdenum – 4750°F
iv. Columbium – 4380°F.
14. Which of the following is/are the limitations of high-temperature non-metallic materials?
a) Lack of ductility
b) Less resistance to thermal shock
c) Weldability, less resistance to thermal shock, lack of ductility and formability
d) Weldability and formability
Answer: c
Explanation: Limitations of high-temperature non-metallic materials are:
i. Lack of ductility
ii. Less resistance to thermal shock
iii. Lack of ductility
iv. Formability
v. Weldability.
