Vol.8 No.2 2015

Research paper : Development of material testing equipment in high pressure gaseous hydrogen and international collaborative work of a testing method for a hydrogen society (T. IIJIMA et al.)−63−Synthesiology - English edition Vol.8 No.2 (2015) threshold test in accordance to ASTM E1681), and (3) crack growth rate da/dN in gaseous hydrogen.[11]-[15] In Europe, high-pressure gas vessels are designated in the European Norm EN13445 (1999, Unfired Pressure Vessels) under PED97/23/EU (1997, Pressure Equipment Directive) that is equivalent to the High-Pressure Gas Safety Laws of Japan, but the evaluation of hydrogen embrittlement of materials follow ISO 11114-4.[16][17] The ISO 11114-4 (2005) requires the hydrogen embrittlement evaluation testing method when Cr-Mo alloy steel with tensile strength up to 950 MPa is used as the material for the gaseous hydrogen pressure vessel with normal operation pressure of 30 MPa or less as follows: (1) a rupture test where a crack is produced by increasing the pressure of gaseous hydrogen applied to one side of a discoid sample, (2) a crack-initiation threshold test where the load is increased in steps in gaseous hydrogen of 15 MPa, and (3) a crack-arrest threshold test at constant displacement or constant load in gaseous hydrogen of 15 MPa. However, since this test pressure in gaseous hydrogen is insufficient for the material testing method of hydrogen station vessels for which the normal operation pressure is 82 MPa, review is being continued for the standard of hydrogen station vessels at the ISO Technical Committee (TC197/WG15).As it can be seen, the material compatibility standards for high-pressure gaseous hydrogen equipment such as FCV on-board containers and hydrogen station vessels are in the process of being established worldwide. Since SUS316L stainless steel and A6061aluminum alloys are expensive, it is necessary to increase the choice of materials that can be used for the vessels and pipes of high-pressure gaseous hydrogen equipment to achieve cost reduction that allows the diffusion of FCVs and hydrogen filling stations. Therefore, for low-alloy steel that has potential to be used in certain conditions although it may be affected by hydrogen embrittlement, it is necessary to consider the material evaluation technologies for fatigue property and fracture toughness in high-pressure gaseous hydrogen condition from the perspective of finite life design, and to establish a method for accurately evaluating the material behavior in high-pressure gaseous hydrogen. We aim to contribute to the international standardization of the testing method of materials compatibility in high-pressure gaseous hydrogen equipment, by developing material testing equipment for high-pressure gaseous hydrogen of 100 MPa or more, obtaining material test data using such equipment, investigating the efficacy of the testing method through accurate evaluation of hydrogen embrittlement phenomena and understanding the embrittlement mechanism, providing and diffusing this knowledge to the industry through creation of a database of the material evaluation results, and approaching the related organizations involved in standard formulation (Fig. 1).3 Development of the material testing equipment for high-pressure gaseous hydrogenGlobally, there are not many research institutes that possess material testing equipment for gaseous hydrogen pressure of over 100 MPa. In Japan, as of October 2014, Kyushu University (120MPa), Energy Technology Research Institute, AIST (120 MPa), and a few private companies have materials testing equipment for 100~120 MPa. In USA, the Sandia National Laboratories (140 MPa); in Europe, The Welding Institute of Britain (100 MPa); and in Asia, China and Korea each has material testing equipment for 120 MPa.In our research group, we accumulated the operational know-how by gradually increasing the pressure of the gaseous hydrogen used from 1 MPa, 40 MPa, 70 MPa, and then to 120 MPa. Based on the know-how, we further improved the safety for experiments using high-pressure gaseous hydrogen in 2011, through simplification of the system by integration of high-pressure gaseous hydrogen gas supply systems, remote control using PCs, introduction of monitoring cameras and an emergency shut-down system, and automation of the testing area by mutual isolation of individual testing devices using protective shields. The fatigue testing device, slow strain rate tensile testing device, and exposure chambers are connected in line to the 120 MPa compressor. The operations of the compressor and each valve are done by remote control using the PC mouse from the control room shown in Fig. 2, and hydrogen gas cannot be supplied all at once to the devices. As shown in Fig. 3, a protective shield is installed in the explosion-proof area surrounded by fireproof walls to isolate the individual testing devices. Moreover, high-pressure gaseous hydrogen is sealed in the test vessel, and after the gaseous hydrogen is introduced into the test vessel, the gas inside the pipes and the compressor is released and decompressed to atmospheric pressure. It is designed so that even if the gaseous hydrogen leaks from the test vessel during the material test, the hydrogen concentration in the Promote material testing method standardizationCreate database of test resultsProvision and dissemination to industriesObtain material test dataInvestigate efficacy of testing methodDevelopment of material testing equipmentFig. 1 Work toward contribution to international standardization


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