API 653 Corrosion & Damage Mechanisms 2

Question 1

Which type of corrosion is characterized by localized attack that produces small pits or holes in the metal surface of a storage tank?

Accepted Answer

Pitting corrosion

Answer

Pitting corrosion produces localized cavities or holes in the metal surface and is particularly dangerous because it can perforate tank walls while overall metal loss remains low.

Question 2

In API 653 context, what is the primary concern with microbiologically influenced corrosion (MIC) in aboveground storage tanks?

Accepted Answer

Sulfate-reducing bacteria can accelerate corrosion on the tank bottom

Answer

Sulfate-reducing bacteria (SRB) thrive in anaerobic conditions under sludge on tank bottoms and can accelerate corrosion significantly, making MIC a critical concern for floor integrity.

Question 3

What is the term for the preferential corrosion that occurs at the junction of two dissimilar metals in an electrolyte?

Accepted Answer

Galvanic corrosion

Answer

Galvanic corrosion occurs when two dissimilar metals are in electrical contact in the presence of an electrolyte, causing the more active (anodic) metal to corrode preferentially.

Question 4

Which damage mechanism causes tank shell cracking when tensile stress combines with a corrosive environment, commonly seen in tanks storing caustic solutions?

Accepted Answer

Stress corrosion cracking

Answer

Stress corrosion cracking (SCC) results from the combined action of tensile stress and a specific corrosive environment, such as caustic stress corrosion cracking in tanks storing sodium hydroxide.

Question 5

What does 'annular plate corrosion' specifically refer to in aboveground storage tank inspection?

Accepted Answer

Corrosion on the bottom plates adjacent to the shell

Answer

Annular plate corrosion refers to corrosion occurring on the tank bottom plates in the area adjacent to and beneath the shell, which is critical because these plates support the entire tank structure.

(API 653) API 653 Aboveground Storage Tank Inspector Certification Practice Test

(API 653) API 653 Aboveground Storage Tank Inspector Certification Practice Test

API 653 Corrosion & Damage Mechanisms 2