According to ISO/TR 17844:2004, cold cracking in high-strength steel welds is primarily driven by three factors: hydrogen content in the weld metal, tensile residual stresses, and a susceptible martensitic microstructure.
Most fabrication codes mandate preheating and interpass temperature control to slow the cooling rate and allow hydrogen to diffuse out of the weld zone. For steels with yield strengths above 690 MPa, even with low-hydrogen welding consumables, the risk of hydrogen-assisted cracking (HAC) remains significant if the heat input is too low.
A common approach in heavy fabrication is to combine preheating with a post-weld hydrogen release soak at 200-300?C for 2-4 hours. This practice is specified in EN 1011-2 for fine-grain structural steels and is often adapted for high-strength quenched-and-tempered grades.
Key considerations for avoiding HAC:
? Maintain a minimum preheat temperature based on carbon equivalent and plate thickness.
? Use low-hydrogen electrodes (H5 or H4 per ISO 3691) and store them properly.
? Control interpass temperature within the WPS range to avoid excessive cooling.
? Apply post-weld hydrogen release if delayed NDT is expected.
For critical joints in offshore or pressure vessel applications, the weld procedure qualification (WPQR) must include a hydrogen cracking test, such as the Tekken test or controlled thermal severity test, to verify the chosen parameters.
How do you verify hydrogen control in your shop: by monitoring consumable storage, or by direct hydrogen measurement in deposited weld metal?
Source: ISO/TR 17844, 2004