Category: Corrosion Engineering Objective Questions

Corrosion Engineering Multiple Choice Questions 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: Galvanic corrosion (dissimilar metal 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
Clarification: 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
Clarification: 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 H₂ 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
Clarification: In EMF series all metals are referenced against the hydrogen electrode (H₂/H+) which is arbitrarily defined as zero. This is known as the Standard hydrogen electrode (SHE). The saturated calomel electrode also acts as a reference electrode based on the reaction between elemental mercury (Hg) and mercury(I) chloride (Hg₂Cl₂). 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
Clarification: Galvanic series is the arrangement of various engineering materials (pure metals and alloys) 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
Clarification: 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
Clarification: 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.

Corrosion Engineering Question Paper 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 (type 430)
c) Titanium
d) High-silicon cast iron, stainless steels, and titanium
Answer: d
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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.

Corrosion Engineering Questions and Answers for Experienced people 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
Clarification: 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
Clarification: 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 (Face centered cubic) 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
Clarification: HCP is abbreviated as hexagonal close packed structure. Conditions for HCP is a₁=a₂≠a₃ and α=β=60, γ̈=120, where a₁, a₂, a₃ are unit vectors in three directions and α, β, γ̈ 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
Clarification: 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
Clarification:
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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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) a₁=a₂=a₃ and α=β=(ddot{gamma})=90
b) a₁=a₂≠a₃ and α=β=(ddot{gamma})=90
c) a₁≠a₂≠a₃ and α=β=(ddot{gamma})=90
d) a₁≠a₂≠a₃ and α=β=(ddot{gamma})≠90
Answer: c
Clarification: 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 a₁≠a₂≠a₃ and α=β=γ̈=90
, where a₁, a₂, a­₃ are unit vectors in three directions and α, β, γ̈ 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) FCCd) HCP>FCC>BCC
Answer: a
Clarification: Packing efficiency = (volume of atoms in unit cell/volume of the unit cell)*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
Clarification: 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
Clarification: 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.

Corrosion Engineering for Experienced people,

Corrosion Engineering Multiple Choice Questions & Answers 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
Clarification: 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
Clarification: 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 (Fabrication history, metallurgical history).

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
Clarification: 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
Clarification: 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 (MDD)
b) Mils per year (MPY)
c) Both MDD and MPY
d) Neither MDD nor MPY
Answer: b
Clarification: 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 (MDD) 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 (ai/D)
b) Corrosion penetration rate = K (ai/nD)
c) Corrosion penetration rate = (ai/nD)
d) Corrosion penetration rate = (ai/nD)
Answer: b
Clarification: The corrosion rate expression that is used for electrochemical techniques to determine corrosion penetration rate is K (ai/nD) where a is the atomic weight of the metal, i is current density (in microamperes per sq. centimeters), 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
Clarification: Corrosion penetration rate = K (ai/nD)
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/cm³
K = 0.129 for steel
Corrosion penetration rate = 0.129 * [(55.8) / (2*7.86)] = 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
Clarification: 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
Clarification: 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
Clarification: 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.

To practice all areas of Corrosion Engineering,