Canadian Welding Bureau (CWB) Level I Practice Exam

Hydrogen cracking happens when hydrogen atoms produced during welding diffuse into the weld metal and collect at stressed or restrained regions as the metal cools, creating fragile microstructures that crack. This is a common issue in many welds, especially with certain steels and high hydrogen content. The most effective prevention is to minimize hydrogen in the weld metal and manage the heat input. Preheating the workpiece raises the weld zone temperature during welding and slows the cooling rate, giving hydrogen more time to diffuse out and reducing the tendency for cracks to form. Using low-hydrogen electrodes minimizes the hydrogen introduced into the weld metal in the first place. Together, these measures address the root cause by limiting hydrogen availability and controlling the solidification and cooling environment. Other ideas, like rust being the cause, don’t reflect the welding mechanism, and relying on welding speed alone doesn’t address hydrogen diffusion and embrittlement.