Abstract
With an accelerated transition in global energy industries toward clean, renewable energy sources, the implementation of hydrogen gas has been proposed as a solution. However, weldments in long-distance pipelines to transport hydrogen are often considered the weakest structural link since they create microstructural heterogeneity, generally categorized into weld metal (WM), heat-affected zone (HAZ), and base metal (BM), with varying degrees of hydrogen compatibility. To ensure pipeline safety for pressurized hydrogen transport, it is essential to evaluate weld susceptibility to hydrogen embrittlement. In this study, the fracture toughness of X65 vintage pipeline steel with a girth weld is investigated in air (reference) and in 200 bar hydrogen gas at room temperature. Two specimen geometries, SENT (a/W = 0.3) and SENB (a/W = 0.5), were extracted from the weld region with the pre-crack located at the fusion line. Crack growth is monitored using a clip gauge, direct current potential drop (DCPD), and a high-speed camera simultaneously. The influence of geometrical constraint on fracture toughness in pressurized gaseous hydrogen is also examined, as this effect has been only limitedly studied in hydrogen. Microstructural characterization and hardness measurements are performed before testing, and post-mortem analyses are conducted to inspect crack paths and fracture surfaces. By comparing resistance curves in air and hydrogen, together with microstructure-dependent crack path analysis, this work provides new insights into the fracture behavior and integrity assessment of hydrogen-exposed pipeline girth welds.