Abstract: Cracks were found on a 00Cr17Ni14Mo2 steel flange when it was ready to be welded and reused after removal. The causes of cracks on the flange were analyzed by means of macroscopic observation, chemical composition analysis, metallographic examination, fracture analysis and mechanical property test. The results show that the cracking nature of the flange was stress corrosion cracking, and the cracks mainly occurred at the position with the maximum tensile stress. The carbon content of the flange was too high, which reduced the corrosion resistance of the material, and finally led flange to cracks.