Abstract: The stainless steel flue gas pipes of YG-1.1-165Q waste heat boiler in a carbon black enterprise cracked in use. The cracking causes of flue gas pipe were analyzed by means of macroscopic analysis, chemical composition analysis and metallographic examination. The results show that the problems of unsuitable material selection of flue gas pipe, poor water quality of boiler and improper bottom drainage led to stress corrosion cracking in flue gas pipe. Finally, the preventive measures were put forward for the cracking of flue gas pipe.