Abstract: Pitting corrosion failure of the carbon steel heat exchanger tubes in delayed coking unit was analyzed with optical microscope,scanning electronic microscope(SEM) and energy diffraction spetroscope(EDS).The results showed that the corrosion products mainly consisted of oxide/hydroxide and chloride of iron.It was oxygen absorption corrosion that resulted in the pitting of the tubes.Oxygen remained in the circulating water was responsible for the oxygen absorption corrosion and chloride in the cooling water accelerated the corrosion process.So key measure to prevent the corrosion of the heat exchanger tubes is controlling the oxygen content in the water.