On the applicability of carbon steels K55 and L80 for underground hydrogen storage

To evaluate the possibility of hydrogen storage in depleted gas reservoirs, natural gas storage facilities, aquifers and salt caverns, the applicability of ferritic pearlitic K55 and tempered martensitic L80, both very frequently used as casings and tubings, has been investigated. Materials were investigated by means of high-pressure, high-temperature autoclave tests and analyses of the hydrogen uptake. The autoclave tests were performed on tensile specimens loaded with a spring at 90 % of the specified minimum yield strength, additionally the samples were analysed to determine the hydrogen uptake. Different gas compositions were considered (pure hydrogen, with or without the presence of CO2/H2S) under a hydrogen partial pressure of 120 bar. The tests were conducted in dry or wet environments. From the results, it can be seen that the hydrogen uptake is low even under the most severe conditions. However, from the mechanical test conducted in this study, it appears that the ferritic pearlitic K55 steel seems to be a suitable pipe material for underground hydrogen storage, and the higher strength steel L80 steel can be used only in non-sour environments (no significant amount of H2S in the reservoir, which is a priori the case of underground storages).