Cl-SCC Attack in SS 316L Branch Connection Welding

摘要

After seven (7) years in service, a failure occurred in an austenitic stainless steel (316L) pipe transferring feed sour gas separated by three phase separator. The gas leak was observed in the vertical relief valve branch connection. Failure analysis confirmed the reason of leak was several cracks developed near the welding joint.The cracks were identified to be chloride stress corrosion cracking Cl-SCC. Although the routine collected sampled from the fed gas streams revealed very low chloride concentrations, the collected sample from the failed spool shown a high concentration up to 300 ppm.rnThe result from a Risk Based Inspection (RBI) assessment for the feed gas stream showed an in-crease in the potential risk in SS 316L piping with increasing the chloride percentage.rnSeveral action plans were evaluated to prevent reoccurrence starting with inspecting all welding joint in the system. The inspection faced difficulty in branch connections where more plans were stated including coating the piping and upgrading the piping material more resistance metal. Inconel 825 was elected to replace SS 316L in the branch connections to insure immune to chloride attacks material. All preventing methods were discussed in this work including the feasibility and cost estimate for each plan.