Abstract: Leakage occurred in the heat exchange tube of an evaporator. The causes of leakage were analyzed by means of macroscopic observation, chemical composition analysis, scanning electron microscope and energy spectrum analysis, metallographic examination，mechanical property test. The results show that the medium in the heat exchange tube was mineral, the impurity components in different minerals were different, and the heat exchange tube was easy to scale after working for a long time. It was necessary to remove the scale by regular pickling, and there was a possibility that the acid was not cleaned after pickling. The medium in the heat exchange tube contained corrosive elements sulfur and chlorine, resulting in corrosion of the inner wall of the pipeline at a higher temperature. In addition, the high-temperature medium in the spiral flow caused the pipeline to continuously tear and peel off the protective film generated by corrosion, resulting in erosion pits and exposing the fresh active metal surface, so that the inside and outside of the erosion pits constituted a corrosion galvanic cell, resulting in further acceleration of corrosion, gradual thinning of the tube wall, and finally leakage of the heat exchange tube.