Abstract: A stainless steel flange experienced a leakage incident during operation. The cause of the flange leakage was analyzed using methods such as macroscopic observation, chemical composition analysis, metallographic examination, scanning electron microscopy and energy spectrum analysis, finite element analysis. The results show that during the manufacturing process, carbides precipitated along the grain boundaries, leading to intergranular sensitization. During operation, stress concentration occurred at the flange neck, ultimately causing intergranular brittle cracking in the flange.