Corrosion Engineering Multiple Choice Questions on “ Eight Forms – Stress Corrosion”.
1. What is the abbreviation of SCC regarding corrosion?
a) Stress-corrosion cracking
b) Stress-cracking corrosion
c) Stress-corrosion contact
d) Stress-contact corrosion
Answer: a
Clarification: SCC can be abbreviated as stress-cracking corrosion. It is referred to the simultaneous action of corrosion and stress on a metal structure. Tensile stress is the most common stress that encounters in the industrial world.
2. Stress-corrosion cracking occurs due to the simultaneous presence of tensile stress and a specific corrosive medium.
a) True
b) False
Answer: a
Clarification: Stress–corrosion cracking occurs due to the simultaneous presence of tensile stress either is caused by residual or external stress and a specific corrosive medium. Residual stress is caused due to welding, cold working, etc.
3. Which of the following is/are the classic examples of stress-corrosion cracking?
a) Season cracking of brass
b) Caustic embrittlement of steel
c) Season cracking of brass and caustic embrittlement of steel
d) Neither season cracking of brass nor caustic embrittlement of steel
Answer: c
Clarification: The two main classic examples of stress-corrosion cracking are:
i. Season cracking of brass
ii. Caustic embrittlement of steel.
4. What is meant by season cracking of brass?
a) Stress-corrosion cracking failure of brass cat ridge cases due to ammonia
b) Stress-corrosion cracking failure of brass cat ridge cases due to caustic soda
c) Stress-corrosion cracking failure of brass cat ridge cases due to caustic soda and ammonia
d) Stress-corrosion cracking failure with brittle fracture
Answer: a
Clarification: Season cracking refers to the stress-corrosion cracking failure of brass cat ridge cases. The main important environmental component in season cracking is ammonia, which results from the decomposition of organic matter.
5. What is meant by caustic embrittlement of steel?
a) Failure of cold-worked rivets by a brittle fracture in the presence of ammonia
b) Failure of cold-worked rivets by a brittle fracture in the presence of caustic soda
c) Failure of cold-worked rivets by a brittle fracture in the presence of caustic soda and ammonia
d) Failure of cold-worked rivets by the cup and cone fracture in the presence of caustic soda
Answer: b
Clarification: Explosions of riveted boilers that occurred in early steam-driven locomotives are due to the cold working during the operation. Hence, brittle fracture in the presence of caustic resulted in caustic embrittlement.
6. In which of the following environments that stainless steel will undergo stress-corrosion cracking?
a) Chlorides
b) Caustics
c) Ammonia
d) Chlorides and caustics
Answer: d
Clarification: Stainless steel undergoes stress-corrosion cracking in chlorides and caustics. They do not crack in ammonia, sulfuric acid, nitric acid, acetic acid, and pure water.
7. Which of the following is/are the most important variables that affect stress-corrosion cracking?
a) Temperature
b) Metal composition
c) Type and amount of stress applied
d) Temperature, metal composition, and type and amount of stress applied
Answer: d
Clarification: The most important variables that affect stress-corrosion cracking are:
i. Temperature
ii. Metal composition
iii. Corrosive solution composition
iv. Type and amount of stress applied
v. Design of metal structure.
8. Which of the following alloy in which both intergranular and trans-granular cracking occurs?
a) High-nickel alloys
b) iron-chromium alloys
c) Brasses
d) High-nickel alloys, iron-chromium alloys, and brasses
Answer: d
Clarification: Stress-corrosion cracking can be intergranular and trans-granular cracking. Alloys such as high-nickel alloys, iron-chromium alloys, and brasses often crack both in intergranular and transgranular manner.
9. Define Threshold stress regarding stress-corrosion cracking.
a) The maximum stress at which the specimen ruptures
b) The maximum stress required to prevent cracking
c) The minimum stress required to prevent cracking
d) The minimum stress at which cracking starts
Answer: c
Clarification: Increasing stress decreases the time before cracking occurs. Threshold stress is the minimum stress required to prevent cracking. It depends on temperature, alloy composition, and environment composition.
10. As stress-corrosion cracks penetrate the material, the cross-sectional area gets reduced under constant tensile load.
a) False
b) True
Answer: b
Clarification: Stress-corrosion cracking is the simultaneous attack of corrosion and stress. A stress-corrosion crack penetrates the material; the cross-sectional area gets reduced under constant tensile stress.
11. Which of the following is/are the environments that cause stress-corrosion cracking to titanium?
a) Red fuming nitric acid
b) Methanol-HCl
c) Nitrogen tetroxide (N2O4)
d) Red fuming nitric acid, methanol-HCl, and nitrogen tetroxide
Answer: d
Clarification: Stress-corrosion cracking is the simultaneous action of stress and corrosive environment on a metal. Red fuming nitric acid, methanol-HCl, and nitrogen tetroxide are the environments that may cause stress-cracking corrosion.
12. Which of the following is/are the metallurgical factors that affect stress-corrosion cracking?
a) Chemical composition
b) Distribution of precipitates
c) Dislocation interactions
d) Chemical composition, distribution of precipitates and dislocation interactions
Answer: d
Clarification: Metallurgical factors that affect stress-corrosion cracking are:
i. Average chemical composition
ii. Preferential orientation of grains
iii. Distribution of precipitates
iv. Dislocation interactions
v. Degree of metastability.
13. Which of the following type of stress has an important role in rupturing protective films during both the initiation and propagation of cracks?
a) Tensile stress
b) Compressive stress
c) Shear stress
d) Compressive and shear stress
Answer: a
Clarification: Tensile stress has an important role in rupturing protective films during both the initiation and propagation of cracks. Breaks in the passive layer of metal induce a rapid attack.
14. Which of the following stress-corrosion cracking mechanism is highly acceptable?
a) Dissolution mechanics
b) Mechanical mechanics
c) Both dissolution and mechanical mechanics
d) Hydrogen mechanics
Answer: a
Clarification: Dissolution mechanics is highly acceptable than mechanical mechanics. The dissolution model describes anodic dissolution at the crack tip, as strain ruptures the passive film at the tip.
15. Which of the following is/are the preventions of stress-corrosion cracking?
a) Lowering working stress below the threshold value
b) Shot peening to produce residual compressive stresses
c) Applying for cathodic protection
d) Lowering working stress below the threshold value, shot peening to produce residual compressive stresses and applying for cathodic protection
Answer: d
Clarification: Methods to prevent stress-corrosion cracking are:
i. Lowering working stress below the threshold value
ii. Shot peening to produce residual compressive stresses
iii. Applying cathodic protection to the structure
iv. Adding inhibitors to the system
v. Eliminating the critical environment species.