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

摘要

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 /= 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, A12O3 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 -/area parameter method was used to estimate the fatigue strength, using the upper limit of the fatigue crack growth acceleration with hydrogen.