Hydrogen compatibility evaluation of ferritic steels using a combined method of small punch test (SPT) and numerical simulation for notched specimens

Hydrogen energy is becoming increasingly important worldwide. Due to cost-effectiveness, ferritic and martensitic steels have been commonly used for hydrogen services such as pipelines and storage tanks. However, these steels are prone to hydrogen embrittlement (HE), which causes ductility loss without affecting yield and ultimate tensile strength. Assessing hydrogen compatibility in terms of strength, especially under localized stress, which might correlate with the relative notch tensile strength (RNTS) is necessary. This study aims to establish a procedure to determine the RNTS through the small punch test (SPT) using U-shaped notch specimens in highpressure environments at room temperature. The notch tensile strength (NTS) was calculated through simulation from the maximum equivalent stress (sigma max) at corresponding fracture displacement (delta f) using the loaddisplacement curve obtained by SPT under each test condition. The combined experiment and numerical approach effectively determined the RNTS, confirming the SPT of notched specimens in screening the HE susceptibility of the steels.