Hydrogen embrittlement induced fracture of 17-4 PH stainless steel valve stem

•The fracture failure of the valve stem on a gate valve of the main pipeline was analyzed.•The main reason for failure is hydrogen embrittlement caused by incorrect aging treatment.•Martensitic and bainitic segregated bands were found, which indicate deficiencies in the casting procedure.•Ensuring high-quality casting and aging treatment avoids hydrogen embrittlement of the valve stem. The 17–4 precipitation hardening (PH) stainless steel (SS) is being widely used in high-pressure corrosive environments due to its high strength and excellent corrosion resistance. Some stems of valves employed in petrochemical pipeline are manufactured from 17-4 PH SS in order to ensure strength, impact toughness and reduce corrosion. Here we presented a rare failure case of 17–4 PH SS. In the present failure analysis, an instantaneous fracture of a valve stem in a pipeline system occurred. The stem was made of 17-4 PH SS and ruptured after a short-term use. A systematic study including metallographic, fractographic, chemical and mechanical analysis was carried out to explore the failure mechanism. The results indicate that incorrect peak-aging treatment and phase segregation induce high hardness and high hydrogen embrittlement (HE) tendency of 17-4 PH SS. It was concluded that, the failure of the valve stem is related to HE at the stress concentration region.