An experimental study for qualifying hydrogen compatibility of austenitic stainless steel under low temperature

Hydrogen compatibility of materials refers to the ability to exhibit reliable mechanical integrity and a probability of failure in a given hydrogen-exposed environment. Currently, no experimental methods for qualifying the hydrogen compatibility of materials have been standardized, and testing expertise has been restricted to only a few laboratories. With international coordination, this paper presents the experimental activities and results to establish a code of practice. The experimental campaign included a slow strain rate tensile (SSRT) test and a notched fatigue life test on SUS316L-grade austenitic stainless steel, which has been widely used in structural components in hydrogen service. Sub-sized tensile specimens were machined from a bar with a gauge diameter of 4.00 mm and a gauge length of 20 mm. A notched specimen with a notch angle of 60 degrees, notch radius of 0.12 mm, and net section diameter of 4 mm was prepared for the fatigue life test. The net section stress in the notched specimen at maximum load (sigma(max)) was 444 MPa in a tension-tension loading condition with a loading ratio of R = 0.1. The tests were performed at a temperature of 233 K (-40 degrees C) in two environmental conditions: high-pressure hydrogen gas at 90 MPa and nitrogen gas at 0.1 MPa (three tests for each condition). No noticeable degradation in yield strength and tensile strength was observed in the specimens tested under hydrogen pressure of 90 MPa H2 at -40 degrees C compared to that tested 0.1 MPa N-2 at -40 degrees C, however, hydrogen had a remarkable effect on reduction area (RA), and strain at fracture. The consistency of the experimental conditions and results from different laboratories with a distinct testing system were closely compared and discussed.