Abstract
Liquid hydrogen LH2 facilities use high-pressure compressed gas cylinders and cryogenic liquid tanks as a main physical hydrogen storage technology. Thus, at almost -253° C at 1.013 bar, 5 Kg H2 is stored in a 75 L liquid H2 tank for instance. At Air Liquide, the stationary storage of hydrogen use type-I tanks mainly made of stainless steel. The austenitic alloys are required with high stability to enhance the γ austenitic phase and ensure the durability of the equipment by avoiding gas leaks due to hydrogen embrittlement phenomena. The few alloys that are compliant with H2 application, are annealed in order to relax the residual stresses, increase the ductility of the material and eliminate the α’ martensite formed by the phase-transformation of the austenite due to cold working.
This study is a part of Air Liquide efforts to enhance security and sustainability of LH2 facilities in partnership with materials suppliers and technical and research institutes. The target here is to assess the influence of the absence of the annealing heat treatment on the microstructure of the austenitic alloy, on the mechanical characteristics and the susceptibility of the material to hydrogen embrittlement. A test protocol has been carried out to analyze the material in terms of chemical composition, microstructure (phase identification, grain size, defects and inclusions), mechanical properties and martensite and ferrite contents. Furthermore, ductility and fatigue tests are performed in LH2 to detect a potential influence of LH2 on the mechanical behavior of the cold worked material. Finally, disks rupture tests are conducted to measure the embrittlement index of the material.
Results are compared to the properties of the equivalent annealed austenitic alloy and the risk of hydrogen embrittlement due to the absence of annealing process is evaluated.