Abstract: The heating surface tube of a coke oven exhaust HRSG leaked. The causes of leakage on heating surface tube were analyzed by means of macroscopic analysis, metallographic examination, scanning electron microscope analysis, energy spectrum analysis, chemical composition analysis, hardness test. The results show that the water quality in boiler was not up to standard, which led to boiling bubble of heating surface tube in high temperature and high pressure operation environment. The corrosion reaction eroded the passivation layer on the inner wall of tube. The corrosion reaction of tube was the most severe and the corrosion depth was the deepest in the water and steam two-phase region, which formed a deepening corrosion groove and eventually led to leakage.