API 571 Hydrogen Damage 2

Question 1

What is the primary mechanism by which H2S promotes hydrogen entry into steel in wet H2S service?

Accepted Answer

H2S acts as a hydrogen recombination poison, allowing atomic hydrogen produced at the steel surface to be absorbed

Answer

H2S prevents atomic hydrogen from safely recombining into H2 gas at the steel surface, forcing the atomic hydrogen to absorb into the metal instead.

Question 2

Which standard test method specifically evaluates steel plate resistance to HIC?

Accepted Answer

NACE TM0284 immersion test in simulated sour solution

Answer

NACE TM0284 is the industry-standard test for evaluating HIC resistance of steel products intended for wet H2S (sour) service.

Question 3

Why does low sulfur content improve HIC resistance of steel plate?

Accepted Answer

Low sulfur means fewer MnS inclusions that serve as hydrogen trap and blister nucleation sites

Answer

MnS inclusions are primary hydrogen trap sites; HIC-resistant steels minimize these inclusions through low sulfur content and calcium treatment to control inclusion shape.

Question 4

HF corrosion in alkylation units can lead to which type of hydrogen damage?

Accepted Answer

Hydrogen-induced cracking (HIC) and hydrogen blistering

Answer

HF acid corrosion generates significant atomic hydrogen as a cathodic byproduct, making HIC and blistering serious concerns in carbon steel equipment in HF alkylation units.

Question 5

Which alloy is the standard material choice for HF alkylation unit equipment due to its HF corrosion resistance?

Accepted Answer

Alloy 400 (Monel — 67Ni-33Cu)

Answer

Alloy 400 (Monel) is the industry-standard material for HF alkylation service due to its excellent resistance to hydrofluoric acid, though welds must be stress-relieved.

API 571 - API 571 Corrosion and Materials Practice Test

API 571 - API 571 Corrosion and Materials Practice Test

API 571 Hydrogen Damage 2