What is a cold crack?

• A. A crack that happens while the weld is still molten.
• B. A crack formed at the weld toe during welding.
• C. A crack formed in service due to corrosion.
• D. A crack that occurs after cooling, often due to hydrogen-induced cracking or high restraint.

Answer: (D)

Cold cracks show up after the weld has cooled. They stem from hydrogen-induced cracking or from high restraint in the joint that leaves tensile residual stresses in the weld and heat-affected zone. Hydrogen from moisture in coatings, flux, or electrode material can diffuse into the metal during welding and become trapped under these stresses; as the metal cools, the hydrogen promotes cracking at lower temperatures. This type of cracking is commonly seen in high-strength steels, thick sections, or joints with significant restraint, and it can be mitigated by proper preheating, using low-hydrogen materials and proper drying, controlling heat input, and applying post-weld heat treatment or reducing restraint.

This differs from cracks that occur while the weld is still molten (hot cracks) or from cracks that appear at the weld toe during welding, or from cracks formed in service due to corrosion.