乙烯裂解气压缩机二段后冷器管束腐蚀原因分析

Corrosion Analysis of Aftercooler Pipeline in the Second Section Coupled to Cracking Gas Compressor of Ethylene Plant

2016年3月,某公司乙烯裂解装置裂解气压缩机二段后冷器(E20202AM/BM)管束发生大面积泄漏,装置被迫临时停工抢修。腐蚀调查和分析认为:装置自2013年脱瓶颈改造后,乙烯裂解气压缩机二段后冷器换热管外壁一直存在以H_2S-CO_2-H_2O为主的腐蚀环境;压缩机段间注水量较大且雾化不良,冷凝液p H值较低,导致二段后冷器换热管外壁发生均匀腐蚀和点蚀,并引起泄漏;在切换真空泵冷凝器(E20225BX/E20226BX)时,因作业不平稳导致裂解气压缩机真空度波动,使得裂解气压缩机二段后冷器管束腐蚀严重部位发生破损穿孔,造成大面积泄漏。2013年改造后壳程介质流速提高以及原料中S含量较高也是导致腐蚀加剧的两个主要因素。建议控制原料S含量、加注缓蚀剂、控制压缩机段间注水量及加强系统管线腐蚀检测抑制腐蚀穿孔发生。

In March 2016,large area leakage accident occurred in the aftercooler（ E20202 AM/BM） pipeline in the second section coupled to cracking gas compressor in an ethylene plant,which resulted in a temporary stoppage for repairs. According to the investigation,a corrosion environment dominated by H_2S-CO_2-H_2O always existed in the outer wall of pipeline; leakage caused by uniform corrosion and pitting appeared in the outer wall of pipeline,due to large injection and poor atomization of water as well as low p H value in the section; damaged perforation occurred in the serious corrosion position of pipeline resulted by the pressure fluctuation in the compressor when switching the vacuum pump condenser（ E20225 BX/E20226 BX）. In addition,two other main factors leading to the intensification of corrosion were the increase of flow velocity in the shell side after modification in2013 and the high content of sulfur in the raw material. Reasonable measures were proposed to prevent the occurrence of corrosion perforation,including controlling sulfur content,adding corrosion inhibitor,governing water injection and improving pipeline corrosion detection.