蒸馏装置塔顶冷凝系统腐蚀及对策

Corrosion of Overhead Condensing System of Crude Distillation Unit and Countermeasures

对某石化分公司10 Mt/a蒸馏装置塔顶冷凝冷却系统腐蚀的原因进行了分析:原油/常压塔顶油气换热器E-102部分管板焊缝及热影响区蚀坑是结垢引起的垢下腐蚀以及HCl露点腐蚀共同作用的结果。结垢及微裂纹的主要原因为常压塔顶系统注剂匹配欠佳、注水量偏低、注水水质不佳及氯化物应力腐蚀开裂,管板在焊接(堆焊)、机加工过程中存在一定的残余应力使管板在拉伸应力和含氯化物水溶液的共同作用下发生氯化物应力腐蚀开裂造成的。原油/初馏塔顶油气换热器E-101管板结垢严重,但腐蚀轻微,其原因为初馏塔顶系统温度较常压塔顶高、冷凝水pH值控制较好且氯离子含量较常压塔顶低。针对以上问题采取了相应对策并对塔顶防腐蚀系统进行了改造,确保塔顶冷凝水pH值控制在6～9,Fe2+和Fe3+质量浓度不大于2 mg/L,取得了良好的效果。

The causes of corrosion in the overhead condensing system of a 10 MM TPY crude distillation unit were analyzed. The corrosion pits in tube sheet welds and heat - affected area of crude/atmospheric distillation tower overhead heat exchanger E - 102 were the results of common effects of under - deposit corrosion and HC1 dew point corrosion. Fouling and micro cracking were mainly caused by inappropriate matching of corrosion inhibitors, lower water injection, low - quality water injection and chloride stress corrosion and chloride stress corrosion cracking under the common effect of residue stress in welding （deposit welding） and processing and water liquid containing chlorides. The tube sheets of overhead oil vapor heat exchanger E - 101 of crude/ preliminary distillation tower suffered from serious fouling but little corrosion. The causes were that the temperature of overhead system of preliminary tower was higher than that of atmospheric tower, the pH value of condensate was appropriately controlled and chlorine ions were lower than those in atmospheric overhead. The tower overhead corrosion protection system has been revamped to ensure that the pH of overhead condensate was controlled at 6 - 9 and the mass concentration of Fe2 ＋ and Fe3＋ was no greater than 2 mg/L. Good results have been achieved.