Failure analysis on abnormal leakage of radiator for high-speed train transformer

The radiator is a sandwich structure with many fins brazed on the clapboards to dissipate the heat generated from the transformers, so it is an important device for ensuring safe operation of the transformers. However, many radiators failed only after one and a half years of service although their design life is five years. For this reason, this paper deeply studied the root causes of abnormal and premature leakage of the radiators for one high-speed train transformer during operation. Firstly, most of the leakages of the radiators were located using X-Ray testing and penetrant testing; then typical leakage areas were carefully selected and sampled for characterization, including metallographic inspection and micro-zone analysis. The analysis results showed that the microscopic holes resulting in the leakages in the clapboard and brazed joint were caused by pitting corrosion along the air side of the clapboard. The inappropriate design of the fin structure and the unqualified brazing process were identified to be the two root causes leading to the pitting corrosion on the clapboard of the radiators. Countermeasures were thus put forward to solve the corresponding problems.