For utilizing fuel cell systems, it is important to establish a design standard for safety. For this purposes, it is necessary to accumulate design data, such as fatigue propagation properties of candidate materials for fuel cell systems equipment. However, fatigue crack propagation tests in a high-pressure H2 gas are difficult, because it is not able to apply crack length measurement instrument such as a microscope as a direct measuring and/or strain gages and a clip gage as an indirect measuring. In this study, a new fatigue crack propagation test with piston displacement aided compliance technique have been proposed for that carried out in high-pressure H2 gas. For verifying its usefulness, fatigue crack propagation properties of SCM435 under 115-120 MPa ultra high-pressure H2 gas were evaluated. It was found that the fatigue crack in H2 gas grew faster about 30 times than that obtained in ambient air.
