By varying the volume of filling material in the environmental chamber,different hydrogen volume/sample notch surface area ratios(RV/S)were obtained.The fatigue life test and scanning electron microscopy(SEM)were used to study the effect of RV/S ratio on the fatigue life of pipeline steel under hydrogen environment.The hydrogen embrittlement theory of spontaneous dissociation of gaseous hydrogen molecules into hydrogen atoms in hydrogen pipelines was discussed.Compared with nitrogen,when RV/S increases from 2.6 mL/mm2 to 24.4 mL/mm2,the fatigue life loss rate of X52 pipeline steel girth weld in high-pressure hydrogen environment increased from 21.2％to 57.2％,the fatigue life loss rate of X52 pipeline steel base material increased from 2.1％to 53.2％,the fracture surface toughness dimples in the fatigue life test rapid tearing zone of X52 pipeline steel girth weld and base environment reduced significantly;there was an increasing trend of defects such as cracks and voids in the ductile dimple area.During the fatigue life test,the crack stop propagating after the initiation of fatigue cracks in nitrogen.However,when the ratio of hydrogen volume to the surface area of the specimen notch was 24.4 mL/mm2,the fatigue cracks continued to propagate once they initiated until the specimen fractured.The RV/S ratio has a significant impact on the fatigue life cycle number of X52 pipeline steel in high-pressure hydrogen environment.The results provided experimental data support for the hydrogen embrittlement theory of spontaneous dissociation of gaseous hydrogen molecules into hydrogen atoms.
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