Hydrogen Cracking — What It Is and Why It Matters
Hydrogen cracking (also called cold cracking, delayed cracking, or hydrogen-induced cracking — HIC) is one of the most serious and insidious weld defects. It occurs hours or even days after welding, when dissolved hydrogen atoms migrate through the solidified weld and base metal, accumulating at stress points and initiating cracks.
Three conditions must be present simultaneously for hydrogen cracking to occur: a susceptible microstructure (hard, brittle martensite in the heat-affected zone), sufficient hydrogen content (from moisture in electrodes, flux, or shielding gas, or from surface contaminants), and tensile stress (residual welding stress or applied loads). Eliminating any one of these three factors prevents the cracking.
Prevention strategies target all three factors: use low-hydrogen filler metals (E7018, properly stored), preheat to slow the cooling rate and prevent martensite formation, maintain adequate interpass temperature, use proper post-weld heat treatment when required, and ensure dry, clean joint preparation. The time delay before cracking appears makes hydrogen cracking particularly dangerous — a weld can pass immediate visual inspection and crack hours or days later.
Frequently Asked Questions
Why does hydrogen cracking happen hours after welding?
Hydrogen atoms are extremely small and mobile. After welding, they slowly diffuse through the metal lattice over hours to days, migrating to high-stress areas (typically the heat-affected zone). When enough hydrogen accumulates at a stress point in a brittle microstructure, the local stress exceeds the metal's reduced ductility, and a crack initiates.
How do I prevent hydrogen cracking?
Use low-hydrogen electrodes (E7018) stored in a rod oven, preheat the base metal per code requirements, maintain interpass temperature, clean joint surfaces to remove moisture and contamination, and apply post-weld heat treatment when the code or WPS requires it. On thick, high-strength, or restrained joints, all three controls should be applied.