Evaluation of Metal Materials for Hydrogen Fuel Stations

Under government funded project: "Development for Safe Utilization and Infrastructure of Hydrogen" entrusted by New Energy and Industrial Technology Development Organization (NEDO), special material testing equipment with heavy walled pressure vessel under 45MPa gaseous hydrogen is facilitated. Tensile properties, strain controlled, low-cycle and high-cycle fatigue and fatigue crack growth tests on CrMo steel (SCM435 (JIS G 4105)) which will be applied for the storage gas cylinders in Japanese hydrogen fuel stations are investigated. The results of the tensile tests under 45MPa ultra high purity hydrogen gas (O2<1ppm) at room temperature shows that there are no difference in yield and maximum tensile strength with those tested in air. However, the reduced ductilities with brittle fracture surface were observed which indicates the occurrence of hydrogen environment embrittlement. It was also found by tensile tests that the embrittling origin is not only caused by machined traces on surface but also by the non-metallic inclusions dispersed on surface. Further discussions on surface treatment effects will be presented. In low cycle fatigue tests, considerable reductions in cycles to failure in 45MPa ultra high purity hydrogen gas were observed. However, there are tendencies that the effect of hydrogen environment embrittlement becomes not so significant as the plastic strain range decreases. It was demonstrated that there was no effect of hydrogen on fatigue limit and this implies that CrMo gas cylinders can be operated in limited fatigue safe condition. Another series of hydrogen test results, temperature effect, fatigue crack growth rate, delayed fracture test using wedge opening loaded specimens, and fatigue test of CrMo gas cylinders under repeated internal pressure with artificial crack will be presented.