A metallurgist is analyzing a failed weld in a high-strength low-alloy (HSLA) steel pipeline. Microscopic examination reveals intergranular cracks in the heat-affected zone (HAZ) that are linked to the presence of non-metallic inclusions and a high degree of through-thickness restraint. The failure occurred during hydrostatic testing, several hours after welding. Which type of cold cracking is most consistent with these observations?
- ASolidification cracking.
- BLamellar tearing.
- CHydrogen-induced cracking (HIC).
- DLiquation cracking.
Show answer & explanationAnswer & explanation
Correct answer: C. Hydrogen-induced cracking (HIC).
The description points strongly to Hydrogen-Induced Cracking (HIC), also known as cold cracking. Key indicators are: 'intergranular cracks in the HAZ' (a common site for HIC), 'high-strength low-alloy (HSLA) steel' (susceptible to HIC), occurrence 'several hours after welding' (delayed cracking characteristic of HIC), and 'non-metallic inclusions' (which can act as hydrogen traps and stress concentrators). High restraint also exacerbates HIC.
Why the other options are wrong
- A. Solidification cracking occurs in the weld metal during solidification and follows dendritic structures, not in the HAZ 'several hours after welding'.
- B. Lamellar tearing occurs in the base metal, parallel to the rolling direction, due to through-thickness stresses acting on elongated inclusions. While through-thickness restraint is mentioned, the cracks are in the HAZ and intergranular, which is not typical for lamellar tearing.
- D. Liquation cracking occurs in the HAZ during welding due to partial melting of grain boundaries, not 'several hours after welding' and is not primarily driven by hydrogen.
Hydrogen-Induced Cracking (HIC)
A type of cold cracking that occurs in the weld metal or heat-affected zone (HAZ) of susceptible steels, often hours or days after welding. It is caused by the synergistic effect of diffusible hydrogen, high tensile stresses, and a brittle microstructure.
- Also known as cold cracking or delayed cracking.
- Common in high-strength steels and steels with high carbon equivalent.
- Hydrogen sources include moisture in consumables, base metal, or atmosphere.
- Prevented by preheating, low-hydrogen consumables, and post-weld heat treatment.
Memory trick: HIC: HAZ cracks, High strength, Hours delayed, Hydrogen's bad play.