According to a 2025 review in Welding in the World, hydrogen-assisted cracking remains a primary concern for high-strength steel welds, particularly in thicknesses above 25 mm. The threshold hydrogen content for cracking drops sharply above 690 MPa yield strength, making consumable selection and preheat critical.
Key control measures from the review include:
• Low-hydrogen electrodes (H4 or H5 classification) and proper storage at 120-150°C.
• Minimum preheat of 100°C for 25 mm plate, increasing to 150°C for 50 mm thickness.
• Post-weld hydrogen bake-out at 200-300°C for 2-4 hours when diffusible hydrogen exceeds 5 mL/100g.
Most fabrication shops still rely on a single preheat temperature regardless of joint thickness or restraint. The review shows that for constrained joints, a 50°C increase in preheat reduces hydrogen concentration by 30% in the heat-affected zone. Auditors typically check consumable handling logs and preheat records, but rarely verify hydrogen bake-out compliance.
The takeaway: hydrogen control must be tailored to actual plate thickness, restraint level, and filler metal diffusible hydrogen. A one-size-fits-all preheat is not enough.
What preheat verification methods do you use on high-strength steel welds?
Source: Welding in the World, 2025