Hydrogen-induced cracking in welded steel is caused by hydrogen diffusion into steel. Which step most directly reduces this risk?

• A. Preheating
• B. Interpass temperature variations
• C. Use high-hydrogen electrode
• D. Rapid cooling after weld

Answer: (A)

Hydrogen-induced cracking happens when hydrogen diffuses into steel during welding and becomes trapped as the metal cools under tensile stresses. Giving the weld and surrounding metal time and temperature to vent hydrogen reduces the chance of crack formation. Preheating the workpiece raises the temperature before and during welding, which slows the cooling rate and lets hydrogen diffuse out more readily while the metal is still warm. This lowers the hydrogen concentration in the weld and heat-affected zone and reduces the development of brittle conditions that lead to cracking. It also minimizes residual stresses and hardness that can contribute to cracking as the metal cools.

Using a high-hydrogen electrode would introduce more hydrogen, increasing risk. Rapid cooling after welding traps hydrogen and raises cracking risk. Controlling interpass temperature variations can influence diffusion between passes, but it’s not as direct or effective as preheating the metal before welding.