Low-Cycle Fatigue Performance of Hydrogen Pre-charged X65 Girth Welds under Seismic Strain Conditions
Abstract
Abstract To ensure the seismic integrity of hydrogen pipelines operating in hydrogen service, particularly in earthquake-prone regions, it is essential to clarify the low-cycle fatigue (LCF) behavior of girth welded joints under hydrogen-affected conditions. In this study, API 5L X65 girth welded joints were tested, using electrochemical hydrogen charging conditions designed to reproduce the hydrogen uptake equivalent to exposure in a 10 MPa hydrogen gas environment. Ex-situ strain-controlled LCF tests were conducted after hydrogen charging to evaluate the influence of pre-charged hydrogen on cyclic deformation and fatigue resistance. The tests were performed on girth welded joint specimens both with and without artificial notches simulating internal weld defects. Two applied strain amplitudes of ± 0.2% and ± 0.5%, corresponding to the expected strain levels under Level 1 and Level 2 seismic motions, respectively, as defined in the Japanese gas pipeline seismic design guidelines, were applied. The results showed that, under all test conditions, the specimens satisfied the required number of loading cycles assumed for seismic events, and no through-thickness fracture was observed. Although hydrogen is generally known to reduce ductility and accelerate crack initiation under cyclic loading, no significant degradation in the seismic LCF performance of the tested girth welded joints was identified under the investigated hydrogen charging conditions. These findings indicate that…
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