Abstract: Leakage happebed on the tube in a shell-tube type heat exchanger during operation, which led to the failure of the heat exchanger. In order to prevent such event, chemical composition analysis, microscopic morphology observation and corrosion product analysis were used to comprehensively study the causes of heat exchange tube failure. The results showed that the content of C in the heat exchange tube was low, decarburization occured on the outer wall, and the thickness of decarburization layer was about 362 μm. The inner wall of the heat exchange tube and the corrosion pit were covered with a large number of flocculent corrosion products, which contained high content of Fe, O, S and C elements. The corrosion products were mainly composed of iron oxides (Fe₃O₄ and Fe₂O₃), iron sulfides (FeS and FeS₂), iron sulfates Fe₂(SO₄)₃ and carbonates (FeCO₃). It was consideered that, under the synergetic effect of H₂S and CO₂, localized corrosion damage happened on the heat exchange tube. H₂S had damaged the FeCO₃ product film on the surface of the heat exchange tube, resulting in the formation of corrosion cells in localized areas of the heat exchange tube, leading to corrosion damage.