API 510 Corrosion, Welding & Material Defects 3

Question 1

Stress corrosion cracking (SCC) in pressure vessels requires which three conditions to occur simultaneously?

Accepted Answer

Susceptible material, tensile stress, and corrosive environment

Answer

SCC requires a susceptible material, a specific corrosive environment (even in trace amounts), and sufficient tensile stress (residual or applied) — all three must be present simultaneously.

Question 2

According to API 510, what is the minimum required thickness formula variable 'C' used for?

Accepted Answer

Corrosion allowance added to calculated minimum thickness

Answer

In API 510 calculations, 'C' represents the corrosion allowance — the extra material thickness added to accommodate future corrosion over the vessel's remaining service life.

Question 3

Which type of cracking occurs in the heat-affected zone (HAZ) of welds in high-strength steels due to hydrogen embrittlement?

Accepted Answer

Hydrogen-induced cracking (HIC)

Answer

Hydrogen-induced cracking (also called cold cracking or delayed cracking) occurs in the HAZ when atomic hydrogen diffuses into the steel lattice, and combined with residual stress, causes cracking after the weld cools.

Question 4

What type of corrosion is most commonly found in stagnant or low-flow areas, crevices, and under deposits on a pressure vessel?

Accepted Answer

Crevice corrosion

Answer

Crevice corrosion occurs in confined spaces where stagnant solution becomes depleted in oxygen and enriched in corrosive ions, creating an aggressive local environment.

Question 5

Which weld defect is caused by gas pockets or voids trapped in the solidifying weld metal?

Accepted Answer

Porosity

Answer

Porosity consists of cavities or pores formed when gas (hydrogen, oxygen, or nitrogen) becomes trapped in the molten weld pool and cannot escape before solidification.

(API 510) Certified Pressure Vessel Inspector Practice Test

(API 510) Certified Pressure Vessel Inspector Practice Test

API 510 Corrosion, Welding & Material Defects 3