Abstract: The cracks were found on the Inconel 800 alloy bellows in a petrochemical company after temporary stoppage. The cracking reason was analyzed by chemical composition analysis, macroscopic and microscopic morphology observation, scanning electron microscopy and energy spectrum analysis, transmission electron microscope analysis. The results show that the sensitization of bellows occurred during application and were in the polythionic acid environment during the stoppage time which resulted in the intergranular corrosion. The microcracks produced by intergranular corrosion were the source of cracks and eventually the microcracks extended and resulted in the formation of stress corrosion cracks under the action of stress.