Causes of Perforation of Air-Cooled Tubes in Desulfurization and Denitrification System in a Coking Plant and Its Preventive Measures

The causes of perforation of air-cooled tubes in desulfurization and denitrification system in a coking plant were analyzed by means of metallographic microscope, scanning electron microscope (SEM), energy dispersive spectrometer (EDS) and X-ray diffractometer (XRD). The results showed that the high-temperature flue gas containing water vapor generated condensate water on the outer wall of the air-cooled tube, and the corrosive media such as SO₂, SO₃, O₂ and Cl^- in the flue gas was dissolved. The condensate water containing corrosive media infiltrated and accumulated at the interface between the air-cooled tube substrate and the enamel layer. The air-cooled tube substrate was corroded to form a relatively single corrosion product α-FeOOH. The α-FeOOH had a porous structure and was attached to the surface of the air-cooled tube substrate, so that the corrosive medium was enriched at the interface between the enamel layer and the substrate, which accelerated the expansion of corrosion and the thinning of the air-cooled tube wall, eventually leading to the penetration of the tube.