Abstract
At present, a lack of fatigue design curves for Cr-Mo steel in high-pressure gaseous hydrogen worldwide impedes the use of the design fatigue curve (S-N curve) evaluation for vessel fatigue design, necessitating reliance on fracture mechanics methods related to the initial crack size. In this study, strain-controlled fatigue tests with a strain ratio of −1 were carried out in 50 MPa gaseous hydrogen to study the low cycle fatigue properties of Cr-Mo steel. Results indicate that hydrogen reduces the fatigue life of 4130X under high strain amplitudes. Under 0.5 % strain amplitude, different from characteristics of ductile fracture in air, the fracture in 50 MPa gaseous hydrogen showed quasi-cleavage and intergranular fracture characteristics. Based on the test results, the S-N curve in 50 MPa gaseous hydrogen was obtained with fatigue life safety factor 20 and stress amplitude safety factor 2. The S-N curve in 50 MPa gaseous hydrogen is under the curve in KD-320.2 M of the 2023 ASME Boiler & Pressure Vessel Code VIII-3, which does not consider the effect of hydrogen, when the number of cycles to failure is less than 1×106. This indicates that the fatigue life calculated by the S-N curve in KD-320.2 M cannot ensure that 50 MPa high-pressure hydrogen storage vessels avoid fatigue failure under high stress amplitudes.
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