This set of Corrosion Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Eight Forms – Erosion Corrosion”.
1. Erosion corrosion accelerates the rate of attack on a metal because of relative movement between corrosive fluid and the metal surface.
a) True
b) False
View Answer
Explanation: Erosion corrosion is one of the types of corrosion that accelerates the rate of deterioration or attack on a metal because of the relative movement of corrosive fluid and the metal surface.
2. Which of the following type of directional patterns usually exhibit by erosion-corrosion?
a) Grooves
b) Waves
c) Rounded holes
d) Grooves, waves and rounded holes
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Explanation: Erosion corrosion results in wear or abrasion of the surface of the metal. It is characterized in appearance by grooves, gullies, waves, rounded holes, and valleys.
3. Which of the following type of corrosion is depicted in the given figure?
a) Uniform corrosion
b) Erosion corrosion
c) Galvanic corrosion
d) Selective leaching
View Answer
Explanation: Erosion corrosion is depicted in the given figure. Erosion corrosion accelerates the rate of deterioration or attack on a metal because of the relative movement of corrosive fluid and the metal surface.
4. Erosion corrosion results when the protective oxide films are damaged and the metal or alloy are attacked at a rapid rate.
a) True
b) False
View Answer
Explanation: As the relative movement of the corrosive solution and the surface of the metal increases the intensity of erosion-corrosion increases. At higher velocities, it results in the damage or worn out of oxide film and it attacks the metal rapidly.
5. Which of the following metals is/are susceptible to erosion-corrosion?
a) Aluminum
b) Lead
c) Stainless steel
d) Aluminum, lead and stainless steel
View Answer
Explanation: Aluminum, lead, copper, and stainless steel are the metals that are susceptible to erosion-corrosion. Because these metals mainly depend on their oxide film for its corrosive resistance.
6. Which of the following type of equipment is/are highly prone to erosion-corrosion?
a) In piping arrangements at elbows and bends
b) Measuring devices such as orifice and turbine blades
c) In piping arrangements at straight lines
d) In piping arrangements at elbows and bends and measuring devices such as orifice and turbine blades
View Answer
Explanation: Erosion corrosion can be affected by the relative velocity of the corrosive solution and metal surface and along with impingement velocity at the edges and turnings. In piping arrangements at elbows and bends and measuring devices such as orifice and turbine blades are the equipment that is prone to erosion-corrosion.
7. Which of the following is/are the characteristics of oxide film that exhibits better resistance to erosion-corrosion?
a) Hard
b) Dense
c) Adherent
d) Hard, dense and adherent
View Answer
Explanation: Erosion corrosion is the type of corrosion that results in mechanical damage of the metal due to the high velocities of corrosive solutions. And a hard, dense, and adherent oxide film can exhibit better resistance to erosion-corrosion.
8. Which of the following characteristics of titanium, makes it resistant to erosion-corrosion?
a) Stability of titanium oxide
b) Instability of titanium oxide
c) The low reactivity of titanium
d) The low reactivity of titanium and instability of titanium oxide
View Answer
Explanation: Titanium is a reactive metal but is resistant to erosion-corrosion in many environments because of the stability of the titanium oxide (TiO2) film. It reforms its oxide layer within a fraction of seconds after wearing out.
9. Which of the following metal is resistant to seawater, chlorides, and fuming nitric acid?
a) Aluminum
b) Lead
c) Titanium
d) Stainless steel
View Answer
Explanation: Titanium is highly resistant to seawater, chlorides, and fuming nitric acid. It is also resistant to erosion-corrosion because of its high reactivity and stability of oxide film.
10. Which of the following environmental factor plays an important role in erosion-corrosion?
a) Velocity
b) Corrosive concentration
c) pH of the environment
d) Relative humidity of the atmosphere
View Answer
Explanation: Erosion corrosion accelerates the rate of attack on a metal because of relative movement between corrosive fluid and the metal surface. It increases as the velocity of the corrosive solution increases.
11. Define critical velocity regarding erosion-corrosion.
a) Velocity at which erosion-corrosion starts
b) Velocity at which erosion-corrosion stops
c) Velocity after which erosion-corrosion increases exponentially
d) Velocity after which erosion-corrosion decreases exponentially
View Answer
Explanation: Critical velocity is the velocity after which the erosion-corrosion increases exponentially. Case 1 (velocity less than critical velocity):
Erosion corrosion increases linearly with increase with velocity.
Case 2 (velocity greater than critical velocity):
Erosion corrosion increases exponentially with increase with velocity.
12. Which of the following metal shows a decrease in corrosion attack with an increase in velocity in fuming nitric acid?
a) Aluminum
b) Carbon steel
c) Stainless steel 347
d) Copper
View Answer
Explanation: Under stagnant conditions, stainless steel 347 in nitric acid is attacked autocatalytically because of the formation of nitrous acid as a cathodic reaction product. An increase in velocity sweeps away the corrosive nitrous acid in the environment.
13. Which of the following is/are the preventions of erosion-corrosion?
a) Selection of better resistant materials
b) Alteration of the environment
c) Applying protective coatings
d) Selection of better resistant materials, alteration of the environment and applying protective coatings
View Answer
Explanation: Methods for minimizing or preventing erosion-corrosion
i. Selection of better resistant materials
ii. Design of equipment
iii. Alteration of environment
iv. Applying protective coatings
v. Cathodic protection of equipment.
14. Which of the following is/are the aspects of design to minimize erosion-corrosion?
a) Increasing pipe diameter
b) Avoiding sharp edges and turnings
c) Readily replaceable impingement plates should be inserted
d) Increasing pipe diameter, avoiding sharp edges and turnings and readily replaceable impingement plates should be inserted
View Answer
Explanation: Design is an important factor to minimize or combat erosion-corrosion. The design includes increasing pipe diameter, avoiding sharp edges and turnings, readily replaceable impingement plates should be inserted, and maintaining certain angles to minimize impingement area.
15. Which of the following is/are the aspects of alteration of the environment to minimize erosion-corrosion?
a) Deaeration of corrosive solution
b) Decrease the temperature
c) Use of Settling and filtration to remove suspended solids
d) Deaeration of the corrosive solution, decrease the temperature and use of settling and filtration to remove suspended solids
View Answer
Explanation: Alteration of the environment is also one of the methods to minimize erosion-corrosion. This includes the deaeration of corrosive solution, decrease the temperature and use of settling and filtration to remove suspended solids.
Sanfoundry Global Education & Learning Series – Corrosion Engineering.
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