Qualification of chromium-molybdenum steel based on the safety factor multiplier method in CHMC1-2014

To clarify the usefulness of the safety factor multiplier method for Cr-Mo steel in the CHMC1-2014 standard for hydrogen-service components, slow-strain-rate tests of smooth and notched specimens and fatigue tests of notched specimens were performed in air and in 115 MPa hydrogen gas. The series of tests determined a safety factor multiplier of ≈3.0, which allowed only quite small design stresses for Cr-Mo steel. Furthermore, the safety factor multiplier can be predicted by fatigue crack growth (FCG) analysis for a notched specimen, i.e., in this respect, the fatigue test of notched specimen is a kind of FCG test. On the basis of this idea, safety factor multipliers for types 304, 316, and 316L austenitic stainless steels were predicted from FCG data to be 2.0, 1.6, and 1.3, respectively. Because the results demonstrate that the safety factor multiplier method provides overly conservative safety factors for some steels, design methods for specific component applications by testing based on design by rule and design by analysis are newly proposed.