API 510 Corrosion Mechanisms & Damage Assessment 4

Question 1

What is 'creep' damage in the context of API 510 pressure vessel inspection?

Accepted Answer

Slow progressive plastic deformation under sustained stress at elevated temperature

Answer

Creep is the time-dependent plastic deformation that occurs when metal is subjected to sustained stress at temperatures above its creep threshold.

Question 2

An API 510 inspector identifies 'blistering' on the interior of a carbon steel vessel in wet H₂S service. What is the most likely cause?

Accepted Answer

Hydrogen pressure buildup at internal laminations or inclusions

Answer

In wet H₂S service, atomic hydrogen diffuses into steel and collects at voids or laminations, building sufficient pressure to form surface blisters.

Question 3

Which corrosion rate formula is used in API 510 to calculate the short-term corrosion rate?

Accepted Answer

(Previous thickness - Current thickness) / Years between inspections

Answer

The short-term corrosion rate uses only the most recent inspection interval: (previous measured thickness − current measured thickness) ÷ years between the two inspections.

Question 4

Intergranular corrosion in austenitic stainless steel is most commonly caused by:

Accepted Answer

Sensitization from heating in the range of 800°F to 1500°F

Answer

Sensitization occurs when chromium carbides precipitate at grain boundaries, depleting adjacent zones of chromium and making them susceptible to intergranular attack.

Question 5

What is 'crevice corrosion' and where is it most likely to occur on a pressure vessel?

Accepted Answer

Localized attack in confined spaces where stagnant solution becomes aggressive, such as under gaskets or deposits

Answer

Crevice corrosion occurs in confined spaces where stagnant solution becomes depleted of oxygen or enriched in corrosive ions, creating a differential concentration cell.

(API 510) API 510 Inspector Certification Practice Test

(API 510) API 510 Inspector Certification Practice Test

API 510 Corrosion Mechanisms & Damage Assessment 4