The effect of hydrogen on the fatigue life of Ni–Cr–Mo steel envisaged for use as a storage cylinder for a 70 MPa hydrogen station

SNCM439 steel specimens cut out from an 80 MPa storage cylinder prototype for a 70 MPa hydrogen station were used for inclusion rating analysis, hydrogen desorption analysis and tension–compression fatigue tests. The fatigue tests were conducted for hydrogen gas-exposed and unexposed specimens. Some specimens contained a small artificial hole, while the others were smooth. The testing frequencies were f = 0.2, 2, 20 and 500 Hz, and the stress ratios were R = −1, 0, 0.3, 0.5 and 0.7. In the smooth specimens, Al2O3 inclusion clusters were the fracture origins. There was an approximately 10-fold acceleration of the fatigue crack growth rates for the hydrogen gas-exposed specimens compared to the unexposed specimens. There was however no clear effect of hydrogen on the fatigue limit. The image parameter method was used to estimate the fatigue strength, using the upper limit of the fatigue crack growth acceleration with hydrogen.