Fracture Toughness Evaluation by Large-Scale Test Under Hydrogen Liquefaction Temperature

Abstract Hydrogen is one of the energy carriers envisioned for achieving a carbon-neutral society. Liquefied hydrogen can be transported in large quantities by ship and is the most economical ways of transportation. In addition, large tanks to store a large amount of liquefied hydrogen are required to economically supply hydrogen to demand sites such as power plants. In order to store liquefied gas of more than 10,000m3, a flat bottom cylindrical tank is assumed. In the wake of the failure of the flat bottom cylindrical tank for LNG in the past, large low-temperature liquefied gas storage tanks should have integrity assessment against fracture, and it is necessary to demonstrate its safety. For example, in the event of a large earthquake, cracks must not initiate in the inner tank, cracks must not propagate unstably, and liquefied gas must not leak. Therefore, the metal materials used in the inner tank are required to have high fracture toughness at temperature of liquid hydrogen. Although it can be evaluated by the tests specified in ASME E1820, evaluation the integrity assessment of the actual structure in an operating environment using a specimen that simulates an inner tank structure is also necessary. The purpose of the present study is to establish a full-scale test technique under hydrogen liquefaction temperature, −253°C (20K) and to evaluate fracture toughness at liquid hydrogen temperature. Cooling equipment using liquefied helium was fabricated and installed on the high load capacity test machine. In the large-scale test, the wide-width-tensile specimen with an initial notch made by SUS316L Multi-pass welded joint was able to be cooled at hydrogen liquefaction temperature during the test, and it was found that the stable ductile crack was initiated and propagated without brittle transition and the tested material had high fracture toughness at 20K.