Hydrogen Embrittlement Behavior in API X52 Steel for High-pressure Hydrogen Transportation

Purpose: The purpose of this study is to understand hydrogen penetration, hydrogen-induced deformation, and fracture behavior in API X52 steel.<br/>Method: Microstructural analysis of API X52 steel was conducted, followed by the slow strain rate test (SSRT) and the small punch test (SPT) in nitrogen and hydrogen atmospheres. The obtained results were evaluated to assess the susceptibility of the material to hydrogen embrittlement.<br/>Results: The SSRT revealed predominantly ductile fractured surfaces in the nitrogen atmosphere specimen, whereas brittle fractured surfaces were observed at the edges. The specimen in the hydrogen atmosphere exhibited elongated dimples and some internal cracks in the central region. The SPT revealed circular cracks and dimples in the nitrogen atmosphere specimen. In contrast, hydrogen atmosphere specimens displayed fractures in the form of a mix of cleavage fractures, dimples, and internal, circumferential, and radial cracks.<br/>Conclusion: Neither band structure nor MnS inclusions significantly influenced hydrogen embrittlement in API X52 steel. Brittle fractures were mainly observed at the grain boundaries of ferrite and pearlite, the primary microstructural constituent, or within ferrite grains.