Abstract：During the use period of one brand of household condensing gas water heater, the false alarms occurred for several times. It was found in maintenance that the leakage of condensate water tank caused the damage of main board. The reason was the corrosion of internal shell and pipeline. The corrosion and leakage of gas water heater once occurred, it may cause risk to personal safety. Therefore, it was of great significance to study the corrosion and failure process, which could prevent recurrence of similar events. In experiments, the micromorphology, composition and microstructure of corrosion products of one condensing gas water heater were analyzed by scanning electron microscopy, energy spectrum composition analysis and metallographic microscopy. The macroscopic morphology and microstructure analysis showed that two areas of heater were seriously corroded, i.e., the flue gas outlet on the top, and male connector of water inlet and outlet on the bottom. The corrosion positions were all located in assembly parts of dissimilar metals. Moreover, the corroded metals were those had lower potential. The energy spectrum composition analysis indicated that the corrosion products contained high content sulfur and oxygen, implying the bimetallic corrosion of metals in humid and corrosive medium containing sulfate. The metallographic analysis showed that the grain boundary precipitates phase existed in structure of male thread of water inlet and outlet. It decreased the corrosion resisting property of material, leading to corrosion cracking along the grain boundary. The cracked metals were peeled off in the form of small piece. Therefore, the connection of dissimilar metals, the sulfide generated in gas combustion and the condensation of water vapor were main reasons for the corrosion and leakage of gas water heater above. It was suggested to improve the materials for heater components. The fabrication using single aluminum could effectively eliminate the potential difference of material and the occurrence of bimetallic corrosion.
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