Abstract: In response to the leakage of the ammonia pipeline in the power plant, the cause of the failure is initially determined through macroscopic observation of the failed pipeline. Then, the failure of the ammonia supply and discharge pipeline is detected through the non-destructive testing, chemical composition analysis, hardness testing, metallographic examination, and other methods. Finally, the test conclusion verifies the leakage causes of the ammonia pipeline is as follows: because the horizontal position of the discharge pipe is lower than the ammonia supply main pipe, water inside the ammonia supply main pipe enters the discharge pipe and then is deposited in the horizontal pipe section in front of the primary and secondary sewage discharge valves; then, the accumulated water is heated, evaporated and concentrated through the heat tracing pipeline, thus the concentration of chloride ions increases, which has strong corrosive effect on stainless steel pipelines. Meanwhile, the preventive measures are proposed based on the causes of failure.