Mechanical Properties of API 5L X65 Linepipe and Girth Welds Under High-Pressure Hydrogen Gas Environment

Abstract As the world strives to achieve carbon neutrality, hydrogen is potentially expected to become one of the major energy sources. Pipelines can be an efficient method for transporting large quantities of gaseous hydrogen, although the choice of appropriate transport methods depends on the conditions of the hydrogen and the distance of transportation. Some researchers have mentioned that carbon steels, commonly used as linepipe in natural gas pipelines, degrade significantly in a high-pressure gaseous hydrogen environment. On the other hand, it has been reported that in a low-pressure hydrogen environment, the reduction in ductility remains at a practically acceptable level. Furthermore, while some papers discuss the properties of linepipes and longitudinal welds, few papers mention results regarding girth welds. Thus, there is a need to investigate the influence of hydrogen on girth welds. In this study, mechanical properties for API 5L X65 pipes and the girth welds produced by the mechanized gas metal arc welding (GMAW) process were investigated through slow strain rate tensile (SSRT) tests and JIC tests under gaseous hydrogen pressure levels of 10, 20, and 90MPa. Then, the critical weld flaw size was assessed by failure assessment diagram (FAD) in accordance with API 1104. The SSRT test results show that 0.2% proof stress and ultimate tensile stress did not influence by hydrogen pressure, while elongation and reduction of area decreased at the range of 0 to 20MPa significantly with increasing hydrogen pressure. In addition, K value, calculated from J values obtained by JIC tests were higher than the specified 55MPa • m1/2, value of ASME B31.12. Moreover, the results of the FAD analysis indicate that even if the weld flaw assumed the workmanship flaw size which is 3mm depth and 25mm length exists at the root area of the weld the pipeline should not be failure.