Abstract: Corrosion failure of heat exchanger tube bundle in oil refinery residue fluid catalytic cracking unit fractionation tower top occured after using for 18 months,the causes were analyzed by scanning electron microscopy,energy disperse spectroscopy and X-ray diffraction.The results show that the outer surface of the heat exchange tube exhibited serious pitting,the maximum depth of corrosion pits was 0.98 mm,accounting for 40.3% of the tube thickness.The corrosion products on the outer surface of the heat exchange tube were mainly α-FeO(OH),Fe2O3,Fe3O4,FeS and FeCl2.The content of corrosive ions (Cl- and S2-) in the media around heat exchange tube outer surface was very high,this was the main reason leading to corrosion failure for heat exchanger tube bundle.