API 571 Stress Corrosion Cracking

Question 1

Stress corrosion cracking (SCC) requires which three factors to be simultaneously present?

Accepted Answer

Tensile stress, corrosive environment, and susceptible material

Answer

SCC initiates and propagates only when tensile stress, a specific corrosive environment, and a susceptible material are all present at the same time.

Question 2

Polythionic acid SCC (PTASCC) in refineries affects which material during which condition?

Accepted Answer

Sensitized austenitic stainless steels during shutdowns in sulfur service

Answer

PTASCC occurs in sensitized stainless steels when polythionic acids form on surfaces during equipment shutdown and air exposure in sulfur-containing service.

Question 3

Caustic stress corrosion cracking of carbon steel is historically known by what other name?

Accepted Answer

Caustic embrittlement

Answer

Caustic embrittlement is the historical term for caustic SCC, first recognized in boiler steels exposed to concentrated sodium hydroxide at elevated temperatures.

Question 4

What post-weld treatment is most commonly applied to prevent stress corrosion cracking?

Accepted Answer

Stress relief post-weld heat treatment (PWHT)

Answer

Stress relief PWHT reduces residual welding stresses below the threshold required to drive SCC initiation in susceptible environments.

Question 5

Liquid metal embrittlement (LME) can occur when carbon steel or other metals contact which substances?

Accepted Answer

Liquid mercury or molten zinc

Answer

LME occurs when susceptible metals contact certain liquid metals such as mercury or molten zinc, causing catastrophic brittle failure at very low applied stresses.

API 571 - API 571 Corrosion and Materials Practice Test

API 571 - API 571 Corrosion and Materials Practice Test

API 571 Stress Corrosion Cracking