What causes hydrogen-induced cracking and what are common mitigation steps?

What causes hydrogen-induced cracking and what are common mitigation steps?

• A. Cracking due to thermal shock; mitigated by rapid cooling.
• B. Oxidation of base metal causing surface rust; mitigated by sanding.
• C. Hydrogen from moisture or moisture-absorbing electrodes; mitigated by drying electrodes, preheating, slow cooling, and low-hydrogen options or PWHT.
• D. Corrosion after welding; mitigated by coating.

Answer: (C)

Hydrogen-induced cracking happens when hydrogen atoms, produced during welding, enter the metal and are driven by residual tensile stresses as the weld cools. Hydrogen is extremely mobile in steel at welding temperatures, so it can diffuse into the weld metal and heat-affected zone and become trapped in microstructural weaknesses, leading to cracks. The most reliable way to prevent this is to minimize the hydrogen that gets into the weld and to give the material a pathway for hydrogen to escape. Drying welding consumables removes moisture that would release hydrogen during welding. Preheating lowers the welding temperature gradient and slows the cooling rate, which reduces hydrogen solubility and helps hydrogen diffuse out rather than become trapped. Slower cooling, or applying a post-weld heat treatment, further relieves residual stresses and provides a route for hydrogen to diffuse away from potential crack paths. Using low-hydrogen electrodes or other low-hydrogen welding options also reduces the amount of hydrogen introduced in the weld. Other options describe different failure modes—thermal shock from rapid cooling, surface rust from oxidation, or general corrosion after welding—not the hydrogen-driven mechanisms responsible for hydrogen-induced cracking.

Hydrogen-induced cracking happens when hydrogen atoms, produced during welding, enter the metal and are driven by residual tensile stresses as the weld cools. Hydrogen is extremely mobile in steel at welding temperatures, so it can diffuse into the weld metal and heat-affected zone and become trapped in microstructural weaknesses, leading to cracks.

The most reliable way to prevent this is to minimize the hydrogen that gets into the weld and to give the material a pathway for hydrogen to escape. Drying welding consumables removes moisture that would release hydrogen during welding. Preheating lowers the welding temperature gradient and slows the cooling rate, which reduces hydrogen solubility and helps hydrogen diffuse out rather than become trapped. Slower cooling, or applying a post-weld heat treatment, further relieves residual stresses and provides a route for hydrogen to diffuse away from potential crack paths. Using low-hydrogen electrodes or other low-hydrogen welding options also reduces the amount of hydrogen introduced in the weld.

Other options describe different failure modes—thermal shock from rapid cooling, surface rust from oxidation, or general corrosion after welding—not the hydrogen-driven mechanisms responsible for hydrogen-induced cracking.