Abstract: A low temperature superheater U-tube burst accident occurred in a new waste heat boiler after less than two months of operation. The causes and mechanism of tube burst were analyzed and determined by macroscopic observation, chemical composition analysis, mechanical property test, metallographic examination, scanning electron microscopy and energy spectrum analysis. The results show that due to the high alkalinity of the boiler water during operation of the boiler, the salt accumulation in the U-tube of the low temperature superheater formed alkali concentration. Under the combined action of cold residual stress of cold roll forming and steam pressure, the alkali stress corrosion crack was initiated at salt deposit. With the passage of time, the crack continued to expand, resulting in the U-tube burst.