Investigation of J-integral in Hydrogen-promoting environment

The conversion of existing natural gas pipelines into hydrogen transport systems is crucial for the sustainable energy transition. To assess the impact of hydrogen-promoting environments on mechanical behavior, it is essential to conduct in-situ testing where hydrogen charging and mechanical testing are performed concurrently. Hydrogen can form on the surface of pipeline metals through dissociation from the gas phase or electrochemical reduction of hydrogen ions via cathodic protection or over protection. Once atomic hydrogen enters the material, it can diffuse rapidly through the metal lattice, accumulating at critical concentrations and leading to "hydrogen damage". The steels used in gas pipelines are immune to hydrogen embrittlement (HE), however HE phenomena can occur under conditions of slow plastic deformation, often due to soil movement. Therefore, it is necessary to perform hydrogen charging in conjunction with mechanical tests, such as elastic-plastic mechanical testing to simulate these conditions. This study investigates the mechanical behavior of API 5L grade X65 pipeline steel. An experimental setup was developed to conduct elastic-plastic fracture mechanics tests on SE(B) samples while concurrently performing electrochemical hydrogen charging. The hydrogen charging was carried out in an alkaline solution, simulating the presence of water in soils. Tests were conducted in both air and hydrogen environments, and the effects of hydrogen embrittlement were analyzed using the J-integral approach.