Insight into the hydrogen permeation and hydrogen embrittlement mechanisms of X52 pipeline steel exposed to gaseous hydrogen

When exposed to gaseous hydrogen, pipeline steel requires the dissociation of hydrogen molecules into hydrogen atoms on its surface before these atoms can diffuse into the steel, a process challenging to observe experimentally. In this study, we demonstrated that hydrogen permeation in X52 low strength pipeline steel occurs in a gaseous hydrogen environment, and slip steps caused by stress or strain under tension at room temperature promote hydrogen dissociation and absorption, resulting in an increase in hydrogen permeation flux. Additionally, slow strain rate tensile tests confirmed the occurrence of hydrogen embrittlement in X52 low strength pipeline steel in gaseous hydrogen. To further elucidate the mechanisms of hydrogen permeation and embrittlement, we employed first-principles method to investigate the dissociation of hydrogen molecules and the pathways for hydrogen atoms to permeate into the steel subsurface.