Category: Corrosion Engineering Objective Questions

250+ TOP MCQs on Environments – Soil and Aerospace and Answers

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

250+ TOP MCQs on Eight Forms – Pitting Corrosion and Answers

Corrosion Engineering Multiple Choice Questions 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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 FeCl3
b) Titanium by sulfuric acid with FeCl3
c) Nickel by sulfuric acid with FeCl3
d) Copper by sulfuric acid with FeCl3
Answer: a
Clarification: 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 FeCl3. 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification:

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
Clarification: 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
Clarification: 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
Clarification: 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 (a small gap) 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
Answer: 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
Clarification: 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
Clarification: The measurement of maximum depth of pit would be a more reliable way of expressing pitting corrosion. As metal loss or metal gain (corrosion product) is very small and does not indicate the depth of penetration.

250+ TOP MCQs on Materials – Other Nonmetallics and Answers

Corrosion Engineering Problems 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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.

Corrosion Engineering Problems,

250+ TOP MCQs on Environments – Petroleum Industry and Answers

Corrosion Engineering Multiple Choice Questions 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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 Na2CrO4.

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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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.

15. Which of the following element is the most beneficial alloying element in steel for resistance to sulfur compounds?
a) Chromium
b) Nickel
c) Molybdenum
d) Carbon
Answer: a
Clarification: 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% H2S in the gas.

250+ TOP MCQs on Corrosion and its Classification and Answers

Corrosion Engineering Multiple Choice Questions 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
Clarification: 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
Clarification: 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) Fe1O
b) Fe2O3
c) Fe3O4
d) Fe(OH)2
Answer: b
Clarification: Corrosion of Iron is generally known as rusting. The chemical reaction can be represented as 4Fe + 3O2 ==> 2Fe2O3.

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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: Corrosion resistant material is the material which has less corrosion rate in a particular atmosphere without much degradation. Stainless steel (an alloy of iron, chromium, nickel) 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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.

250+ TOP MCQs on Eight Forms – Intergranular Corrosion – 1 and Answers

Corrosion Engineering Multiple Choice Questions 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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) Cr3C
b) Cr5C3
c) CrC
d) Cr23C6
Answer: d
Clarification: 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 (Cr23C6) 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
Clarification: !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
Clarification: 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
Clarification: Rapid corrosion attack in impoverished or chromium depleted zone is due to
i. Less corrosion resistance (As chromium% is decreased)
ii. Two dissimilar metal compositions are in contact (Galvanic effect)
iii. Large unfavorable area ratio is present (Area effect)

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
Clarification: 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
Clarification: 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
Clarification: 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 (sensitization 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
Clarification: 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
Clarification: 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
Clarification: 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.