CORROSION CAUSE ANALYSIS OF COAL ECONOMIZE TUBE IN A REGENERATIVE BOILER
余热锅炉省煤器管腐蚀原因分析

Several coal economizer tubes of a regeneration boiler were taken during overhaul. By way of chemical composition analysis and mechanical property examination, results show that the tube is accord with standard. Through appearance inspection, wall thickness measurement, EDS analysis and X- ray diffraction, the corrosion cause of the coal economizer tube is analysed. Results show that since the regeneration boiler uses gas as fuel with a fluctuation of the total sulphur content, a main part of the sulphur changes into SO2. Among which, some can be oxidized into SO3. Then SO3 reacts with vapor and the condenses as H2SO4 at low tepmerature part of coal economizer. Corrosion product analysis makes sure that the corrosion product is ferrite sulphate in corrosion pits. There are other sulphates accreted on the outer surface of tubes. Thereby it is approved that local corrosion is due to sulphuric dewpoint corrosion. The depth of the formed pits may reach 0.9 mm and they seem to be connected each other. So that the tubes are hard to meet the operation requirement of coal economizer. In the inner surface of tubes corrosion product mostly is Fe2O3. This makes sure the inner surface is suffered from uniform corrosion due to deoxided water.