Abstract: The elbow of the sampling pipe for the high temperature reheat steam drain tank level gauge in a power plant leaked during operation. The causes of elbow leakage were studied using macroscopic observation, chemical composition analysis, metallographic examination and hardness testing. The results shows that stress corrosion cracking occurred in the elbow, improper control of the heat treatment process during the manufacturing of the elbow, and accumulation of water at the lower part of the inner wall provided a corrosive environment, ultimately led to cracking and leakage of the elbow.