Category: Corrosion Engineering Objective Questions

Corrosion Engineering Multiple Choice Questions 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: Types of diffusion coatings:
i. Sherardizing – zinc
ii. Chromizing – chromium
iii. Alonizing – aluminum
iv. Carburizing – carbon
v. Nitriding – nitrogen.

Corrosion Engineering Questions & Answers for Exams 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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(s) of polarization is depicted in the given figure?

a) Activation polarization
b) Concentration polarization
c) Activation and concentration polarization
d) Resistance polarization
Answer: c
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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.

Corrosion Engineering Multiple Choice Questions 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
Clarification: 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
Clarification: 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 FeCl₃ 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
Clarification: 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
Clarification: 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+O₂
b) 18Cr-8Ni in H₂SO₄+Fe⁺³
c) Fe in H₂O+O₂
d) 18Cr-8Ni in HNO₃ + Cr₂O₃
Answer: b
Clarification: Initially corrosion rate of Stainless steel (18Cr – 8Ni) 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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 H₂SO₄
c) 18Cr–8Ni in H₂SO₄
d) 18Cr–8Ni in H₂SO₄+Fe⁺³
Answer: d
Clarification: Stainless steel in H₂SO₄ 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.

Corrosion Engineering Multiple Choice Questions 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: Fatigue limit is the stress below which metal will endure an infinite number of cycles without fracture. The fatigue limit can be calculated by (SN curve) 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
Clarification: 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
Clarification: 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
Clarification: The factors that influence corrosion fatigue:
• Type of metal (FCC, BCC, HCP)
• 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
Clarification: 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
Clarification: 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.

Corrosion Engineering Assessment Questions and Answers 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
Clarification: 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
Clarification: Bonderizing, parkerizing, and chromatizing are examples of chemical conversion. Automobile bodies are best known for phosphatizing treatment. Anodized aluminum with a protective film Al₂O₃ 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: Coal-tar coatings are excellent corrosion resistant to fresh, seawater, and soil immersion. Whereas its abrasive resistance and stability of coating are its limitations.

Corrosion Engineering Assessment Questions,