Failure analysis on abnormal leakage of TP321 stainless steel pipe in hydrogen-eliminated system of nuclear power plant

Failure analysis is carried out on a leaked Type 321 stainless steel pipe in the hydrogen-eliminated system of a nuclear power plant. Comprehensive characterizations are utilized to investigate the operation conditions, base materials and macro/micro-morphologies of the failed pipe. Two distinct areas of morphologies inside the pipe are observed and three types of inclusions of the base materials are identified. Analysis results revealed that root cause of the abnormal leakage of the stainless steel pipe was the pitting corrosion, which was induced by chlorides from coastal atmosphere. The relevant failure mechanisms of the leaked stainless steel are carefully discussed and effective countermeasures are put forward as well.