烟气脱硫装置换热器腐蚀原因分析

Analysis on Corrosion of Heat Exchangers in Flue Gas Desulfurization Unit

某公司催化烟气脱硫装置运行一段时间后,换热器腐蚀泄漏问题非常严重。现场调查发现焊缝及热影响区腐蚀最严重,其次是堆焊层和不锈钢复合板。换热器主要的腐蚀类型有点蚀、晶间腐蚀和缝隙腐蚀。通过模拟现场工况进行的实验室评价,对腐蚀发生的原因进行分析,并提出了防腐蚀建议。实验结果表明,脱硫系统中主要的腐蚀性介质有硫酸和亚硫酸、氧气、元素硫,氯离子等。稳定化处理的321不锈钢在现场贫胺液中对氯离子引起的点蚀并不敏感,点蚀发生的原因可能是材料热处理不当或元素硫腐蚀。浸泡试验结果表明,现场贫胺液腐蚀性极强,p H值小于4时,321不锈钢在该介质中极易发生缝隙腐蚀,经敏化处理比未经敏化处理的试样腐蚀速率高,腐蚀更严重。敏化处理后,腐蚀速率高达0.035 mm/a。

The FCC flue gas desulfurization unit in Ji＇nan Petrochemical Company suffered from serious corrosion leakage after operating for a period of time. The field investigation found that the welds and heat affected zone were corroded seriously,followed by surfacing layer and 321 stainless steel composite panels. The main corrosions of the heat exchangers are pitting corrosion,intergranular corrosion and crevice corrosion. The laboratory evaluation was made to simulate field conditions,and the causes of corrosion were analyzed. Corrosion prevention recommendations were proposed. The results showed that,the main corrosive media in the desulfurization system were sulfuric acid and sulfurous acid,oxygen,sulfur,chlorine ion,etc. In the lean amine liquid,the 321 stainless steel after stabilization treatment was not sensitive to pitting corrosion. The causes of pitting corrosion may be the inappropriate material heat treatment or elemental sulfur corrosion. The submerged test results showed that the corrosivity of the lean amine liquid was very strong. When p H value was 4,the 321 stainless steel was easily subject to the crevice corrosion in this medium. The corrosion rate of sensitizing treatment sample was higher than that of not sensitizing treatment sample,and the corrosion was also more serious. After sensitizing treatment,the corrosion rate of sample was as high as 0. 035 mm/a.