When does hydrogen induced cracking occur?

When does hydrogen induced cracking occur?

• A. During Welding
• B. After The Weld Has Cooled
• C. Before Welding
• D. During Post-Weld Heat Treatment

Answer: (B)

Hydrogen-induced cracking is a delayed cracking phenomenon in steels caused by diffusible hydrogen moving under tensile stress and segregating at grain boundaries or other weaknesses. In welding, this most often shows up after the weld has cooled. During welding, hydrogen is drawn into the weld metal, but the metal is hot and more ductile, and the cracks aren’t as likely to form immediately. As the weldment cools, residual tensile stresses remain locked in, and the hydrogen that entered can diffuse to vulnerable sites and initiate cracks in the heat-affected zone or weld toe. This is why the cracking tendency is described as occurring after the weld has cooled. Activities like post-weld heat treatment can relieve these stresses and reduce the risk, whereas pre-weld conditions lack the hydrogen source, and the immediate welding phase is less favorable for hydrogen cracking to become established.