Abstract: Partial heating surface tubes of two waste heat boilers in a gas power unit leaked during the trial operation. The causes of tube leakage were analyzed by means of macroscopical observation, chemical composition analysis, mechanical property test, metallographic examination, scanning electron microscope, energy spectrum analysis and X ray diffraction. The results show that there were more corrosion products on the inner wall of the leakage tubes, and the corrosion products were the oxides of iron. The composition of the corrosion products and the morphology of the corrosion pit indicate that local oxygen corrosion had occurred on the inner wall of the tubes. The corrosion part became thinner and the pit was formed, and the perforation and leakage occured in the serious corrosion.