Abstract: The connecting elbow of the low temperature superheater of a waste heat power generation boiler was cracked after three months of operation.By means of macroscopic observation,chemical composition analysis,hardness test,metallographic inspection and energy spectrum analysis,the reasons for the cracking of the connecting elbow were analyzed.The results showed that the reason for the cracking of the connecting elbow was that during the boiling process after the boiler was installed,the lye entered the superheater,and accumulated and concentrated at the weld on the inner surface of the connecting elbow.Under the combined action of high temperature and various stresses such as pipeline weight,steam-water vibration,thermal stress and structural stress,alkali embrittlement cracking occurred at the weld of the connecting elbow.