CWI Metallurgy and Weld Discontinuities 5

Question 1

What is Post-Weld Heat Treatment (PWHT) primarily used to achieve in weld joints?

Accepted Answer

Relieve residual stresses and improve toughness

Answer

PWHT (stress relief heat treatment) reduces residual stresses from welding, softens the HAZ, improves toughness, and allows hydrogen to diffuse out of the weld.

Question 2

Which term describes the phenomenon where ferrite forms preferentially at prior austenite grain boundaries in the HAZ of carbon steel?

Accepted Answer

Grain boundary ferrite

Answer

Grain boundary ferrite (allotriomorphic ferrite) forms along prior austenite grain boundaries during cooling, which can reduce toughness when it forms a continuous network.

Question 3

A weld inspector observes cracks at the weld toe on a high-strength steel structure found during inspection 48 hours after welding. The most likely cause is:

Accepted Answer

Hydrogen-induced delayed cracking

Answer

Delayed hydrogen-induced cracking (cold cracking) can occur hours or days after welding completion as hydrogen diffuses to areas of high stress concentration such as the weld toe.

Question 4

Which type of porosity consists of a single pore larger than the maximum allowable by code, isolated in the weld?

Accepted Answer

Individual or isolated porosity

Answer

Isolated (individual) porosity refers to a single pore that is separated from other pores by a specified minimum distance, evaluated against size limits in the applicable code.

Question 5

What is 'burn-through' in welding?

Accepted Answer

A hole or void completely through the weld or base metal caused by excessive heat

Answer

Burn-through occurs when excessive heat input melts completely through the joint, creating a hole in the weld or base metal.

CWI Practice Test

CWI Practice Test

CWI Metallurgy and Weld Discontinuities 5