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 happens when hydrogen atoms enter the weld metal or heat-affected zone and, under the influence of residual tensile stresses, diffuse to and accumulate at flaws or grain boundaries. The material is most vulnerable as it cools and residual stresses remain, allowing the trapped hydrogen to cause brittle fractures. That makes cracking most likely to occur after the weld has cooled, not during welding or in other steps. Post-weld heat treatment can relieve stresses and let hydrogen diffuse out, reducing the risk, so it isn’t the typical moment when cracking initiates.