Failure Analysis on Leakage of Stainless Steel Elbow

A certain stainless steel nitrogen gas supply pipeline experienced gas leakage during use, and preliminary inspection confirmed that it was caused by corrosion perforation in the heat affected zone of the elbow weld. Through the use of macroscopic observation, physical and chemical testing, scanning electron microscopy observation, and energy spectrum analysis, the cause of the leakage was carefully analyzed. The results show that the inner and outer surfaces of the weld contained elements such as S and Cl, and there were intergranular corrosion and pitting corrosion in the heat affected zone of the elbow. Improper control of process parameters during elbow welding resulted in sensitization in the heat affected zone, leading to intergranular corrosion. During the pipeline manufacturing process, acid pickling and passivation exacerbated intergranular corrosion of stainless steel, causing pitting corrosion and leakage under the influence of some hazardous elements. Finally, corresponding improvement measures were proposed to ensure the safe operation of the system.