Feasibility Analysis and Verification of 4K Cryogenic Charpy Impact Test Method Using Liquid Helium

This study investigates and validates the feasibility of a Charpy impact testing methodology conducted at 4K ultra-cryogenic temperatures using liquid helium (LHe). Conventional cryogenic impact tests are primarily performed at 77K using liquid nitrogen; however, with the increasing demand for hydrogen energy systems operating at lower temperatures, evaluating mechanical properties at temperatures below 20K has become essential. In this context, a new approach was developed to cool ISO 148-1 standard 316L stainless steel specimens by directly injecting LHe into a specially designed containment system. The injection was performed at a pressure of 9 psig, and it was experimentally confirmed that the specimen core temperature stabilized at approximately 4K within 45 seconds after LHe exposure. Subsequent Charpy impact testing at this temperature demonstrated reliable and repeatable results, confirming that sufficient thermal equilibrium had been achieved. The study not only demonstrates the technical feasibility of this cooling approach but also provides supporting data on the stability and reproducibility of mechanical property evaluation under ultra-low temperatures. In particular, the results offer significant insight into material behavior relevant for components exposed to cryogenic hydrogen conditions, such as storage tanks, transfer lines, and safety valves. The proposed methodology overcomes practical limitations of traditional testing setups by allowing efficient specimen cooling without requiring full-system cryogenic insulation. Therefore, this work provides a crucial reference framework for future material development and testing in support of next-generation hydrogen infrastructure, where accurate property data under extreme cryogenic conditions is critical for safe and efficient system design.