Influence of X65 Girth Welding Parameters on Fracture Toughness in High Pressure Hydrogen

Abstract To reduce carbon dioxide emissions, hydrogen is expected to be used increasingly as a fuel to supplement or replace natural gas. High pressure pipelines have been identified as the most efficient means of transporting hydrogen, and as a result, hydrogen-compatible pipeline networks must be developed. The largest challenge in developing new pipelines or repurposing existing natural gas pipelines for hydrogen service is gaseous hydrogen embrittlement of pipeline materials, particularly steels. Many studies have focused on the testing methods used to study gaseous hydrogen embrittlement, and much of the characterization to date has been on pipe body and seam welds. Relatively few studies have considered pipeline girth weld response to gaseous hydrogen, and even fewer studies have considered the influence of varied welding procedure specifications (WPS) on girth weld hydrogen response. In this research, girth welds were produced on a 508 mm x 12.7 mm (outer diameter x wall thickness) API 5L X65 pipe using several WPSs that included variations in filler metal, preheat temperature, heat input, and single vs. dual torch configuration. The fracture toughness of the weld metal and heat affected zone (HAZ) were evaluated using ASTM E1820 rising displacement tests in high pressure hydrogen. The geometry and hardness of the welds were also characterized using light microscopy and automated Vickers microhardness testing. The fracture toughness, geometry, and hardness results were then used to identify trends in girth weld hydrogen response as a function of welding parameters.