Technical Inspection of a Failed 15-5PH (UNS S15500) Stainless Steel Lower Stem of Surface Safety Gate Valve

In this study, failure of a 15-5PH precipitation hardening stainless steel stem which is installed in a hydraulic surface safety gate valve working in a sour gas environment is investigated. A fluctuating axial load is applied to the stem during its operation. Hydrogen probes were used to measure the penetrated hydrogen ions in the permanent hydrogen traps of the microstructure. SEM micrographs of the failed section were examined. Results of failure analysis on the stem indicate that the fracture failure of the stem was caused by sulfide stress cracking (SSC), which is progressed transgranularly in the martensitic matrix.

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