Hydrogen-induced fracture relocation in a 24-year-serviced X52 pipeline weld

Abstract

Repurposing aged natural-gas pipelines for hydrogen service requires evidence from actual pipes and welded joints because long-term service history and weld heterogeneity are not captured by tests on newly manufactured plate. Here, we evaluated a spiral submerged-arc-welded API 5L X52 pipeline removed after 24 years of service and subsequently subjected to a 257-day field-scale static gaseous-hydrogen exposure at approximately 1.22 MPa. The base metal, heat-affected zone, and weld metal were examined by optical metallography, HV10 hardness, Charpy impact testing at 0 °C, slow-rate tensile testing, and fractography. Hydrogen exposure caused no systematic reduction in hardness, yield strength, or ultimate tensile strength, but consistently reduced tensile ductility. At crosshead rates of 0.10 and 0.05 mm/min, the reduction of area decreased by 11.6% and 12.3% in the base metal and by 12.2% and 14.6% in cross-weld specimens, respectively; cross-weld elongation decreased by 13.3% and 17.2%. More importantly, the documented cross-weld fracture location shifted from the base metal before exposure to the heat-affected zone after exposure. Fracture morphology changed from deep dimpled rupture toward mixed ductile/quasi-cleavage fracture with secondary cracking, while the heat-affected zone also retained the lowest mean impact energy and the greatest scatter after exposure. These results show that stable global strength can mask hydrogen-induced redistribution of local damage and support weld- and heat-affected zone-specific qualification of aged pipelines considered for hydrogen service.

The authors' abstract, as published at the source. Journal of Materials Research and Technology, 2026 · DOI ↗