API 510 Corrosion Assessment 5

Question 1

Which type of corrosion produces a series of small, deep cavities penetrating into the metal while leaving surrounding areas relatively unaffected?

Accepted Answer

Pitting corrosion

Answer

Pitting corrosion is a localized form that creates deep, narrow cavities while surrounding metal remains largely intact, making it particularly dangerous and hard to detect.

Question 2

High-temperature hydrogen attack (HTHA) in pressure vessels primarily causes which type of damage?

Accepted Answer

Decarburization and fissuring of the steel

Answer

HTHA causes decarburization as hydrogen reacts with carbides in the steel, forming methane gas that creates fissures and significantly degrades mechanical properties.

Question 3

What is the most reliable method for an API 510 inspector to distinguish between active pitting corrosion and old, inactive pits?

Accepted Answer

Comparison of pit depth measurements between inspection intervals

Answer

Comparing pit depth measurements from successive inspections reveals whether pits are growing (active) or stable (inactive), providing direct evidence of activity.

Question 4

Under API 510, which assessment method may be used to evaluate pressure vessels with localized metal loss that does not meet minimum thickness requirements?

Accepted Answer

API 579 Fitness-for-Service (FFS) assessment

Answer

API 579 FFS assessment provides analytical methods to evaluate whether vessels with local metal loss can continue safe operation despite falling below nominal design thickness.

Question 5

A carbon steel vessel operating in a caustic (NaOH) service exhibits cracking along welds. Which corrosion mechanism is MOST likely responsible?

Accepted Answer

Caustic stress corrosion cracking (caustic embrittlement)

Answer

Caustic embrittlement is the preferential cracking of carbon steel in NaOH environments, particularly at welds where residual tensile stresses are high.

(API 510) API 510 Inspector Certification Practice Test

(API 510) API 510 Inspector Certification Practice Test

API 510 Corrosion Assessment 5