高压换热器内腐蚀原因的判别与预防

对润滑油高压加氢装置循环氢/热高分油气换热器内腐蚀进行宏观检测、远场涡流检测、常规涡流检测以及垢样分析,采用热力学定量计算判定了腐蚀原因,并提出了相应的预防措施。结果表明,腐蚀集中在管程出口处以及靠近管板部分的换热管,腐蚀产物中存在大量氯化铵盐结晶,腐蚀发生的原因为氯离子腐蚀和NH4Cl盐垢下腐蚀。实践表明在管壳程温度相对较低工况时,将注水由空冷前改为换热器管程入口前,并适当提高注水量和循环氢流量可以有效消除管程内的氯化铵盐,防止管束堵塞,在正常生产中严格控制管程出口温度不低于135℃,可以防止液态水的生成,消除氯化铵盐溶解带来的对奥氏体不锈钢敏感的氯离子腐蚀、铵盐垢下腐蚀和电化学腐蚀。

Recognition of Causes of Internal Corrosion of HP Heat Exchangers and Corrosion Protection

The internal corrosion in the recycle hydrogen/Hot HP separator oil vapor heat exchangers in HP lube oil hydrotreating unit was examined by macro testing,vortex testing,conventional vortex testing and fouling sample analysis.Thermal dynamic analysis was applied to determine the corrosion causes,and corresponding preventive measures were suggested.The results showed that the corrosion mainly concentrated at the outlet of tube side and heat exchange tubes near the tube sheet.The corrosion products contained a large amount of crystal salt of ammonia chloride.The corrosion was the corrosion by chlorine ions and underdeposit corrosion of NH4Cl.The practice demonstrated that the ammonia chloride salt in tube side could be effectively removed and tube plugging can be eliminated by lowering shell side temperature,injecting water at the inlet of heat exchanger tube side instead of at the upstream of air cooler and properly increasing the injection water and recycle hydrogen flowrate.In addition,strict control of tube side outlet temperature at no lower than 135°C could prevent the formation of liuquid water,minimize the chlorine corrosion of austenitic steel by dissolution of ammonia chloride,deposit corrosion of ammonia salt and electric-chemical corrosion.