Abstract: The heat exchange tube of the equipment is made of 10^# steel, and its outer surface is treated by hot dipping zinc. After the equipment was used for more than four years, different degrees of corrosion and leakage occurred on the outer surface of heat exchange tube. In this paper, the failure mode and reason are found by macro inspection, composition and structure analysis, corrosion characteristic analysis and water quality analysis: pitting corrosion is the failure mode. One reason for the corrosion is that the free zinc layer on the surface of the galvanized layer is thin or discontinuous, and ζ phase layer loose and thick, reducing the corrosion resistance of zinc coating. The other is that the water quality exceeds the standard, forming a strong corrosive environment.