Abstract: A leak occurred in the process gas inlet pipeline of a pressure vessel at a fertilizer plant. The chemical composition, mechanical properties, metallographic structure, fracture morphology and scale composition of the leaking pipeline were analyzed. The results showed that the stainless steel leakage in the process gas inlet of the pressure vessel was caused by chloride stress corrosion cracking (SCC). The main factors affecting the SCC of the pipe were the chlorine element in the process medium and the welding quality. It is recommended to strengthen the welding quality, conduct post-weld heat treatment on the welded joint, strengthen the control of surface quality, or replace the material to avoid chloride stress corrosion.