余热锅炉省煤器管腐蚀原因分析

 对在役使用的余热锅炉省煤器管进行了现场取样，经化学成分分析、机械性能测试，省煤器管束符合材质要求.通过外观检验、壁厚测量、扫描电镜、能谱和X射线衍射，对省煤器管腐蚀原因进行了分析.结果表明，余热锅炉以瓦斯气作为燃料，总硫含量波动大，硫分在燃烧时绝大部分变成了SO2，其中有一部分可进一步氧化成SO3，SO3与水汽作用而在省煤器低温部位凝结成H2SO4.腐蚀产物分析证实蚀坑内腐蚀产物为硫酸铁，管外表面附着物经检测也有其它硫酸盐形式.证实管外表面蚀坑处于易于形成露点的位置管材外表面局部腐蚀是因露点腐蚀造成.露点腐蚀蚀坑深达0.9mm，并已连片出现，难以满足省煤器管使用条件.管内表面腐蚀产物主要为Fe2O3，说明管内表面受除氧水均匀腐蚀. 

CORROSION CAUSE ANALYSIS OF COAL ECONOMIZE TUBE IN A REGENERATIVE BOILER

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.