Abstract: During the hydraulic test of a newly installed waste heat boiler, the superheater tube leaked repeatedly. The leakage causes of the elbow were analyzed by means of penetrant testing, chemical composition analysis, metallographic examination, mechanical property test, energy spectrum analysis and finite element simulation. The results show that the operating environment of the superheater tube had the conditions for alkali stress corrosion, and Na⁺ was detected in the corrosion products. The main reason for the leakage of the superheater tube was the cracking of the material caused by alkali stress corrosion, which led to the leakage of the weld, elbow and other parts with large stress concentration.