Category: Corrosion Engineering Objective Questions

Corrosion Engineering Multiple Choice Questions 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
Clarification: 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
Clarification: 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 (anode) and decreases on high corrosion-resistant metal (cathode).

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
Clarification: 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
Clarification: Battery is a combination of cells in which chemical energy is converted into electrical energy. Carbon (noble electrode) acts as cathode and zinc (active electrode) 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
Clarification: 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
Clarification: The conditions to measure the standard reduction potential of metal electrodes against standard hydrogen electrode (SHE) 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
Clarification: 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
Clarification: 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
Clarification: EMF is abbreviated as an electromotive force. It is defined as the potential difference between two points (cathode and anode) 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
Clarification: 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 (passive) and Inconel (active)
c) 18-8 stainless steel (active) and 18-8 stainless steel (passive)
d) Titanium and lead

Answer: a
Clarification: 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 (active or passive). Monel (70 Ni, 30Cu) 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
Clarification: 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
Clarification: 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
Clarification: 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 (z) is 73.

Corrosion Engineering Multiple Choice Questions 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
Clarification: 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
Clarification:
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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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.

Corrosion Engineering Multiple Choice Questions 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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.

Corrosion Engineering Interview Questions 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
Clarification: 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
Clarification: Corrosion occurs due to the presence of oxygen and moisture (electrolyte). 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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.