加氢装置塔顶馏出线弯头腐蚀泄漏分析及防护

某石化公司直馏柴油加氢装置主汽提塔塔顶馏出线弯头部位注剂点下方发生腐蚀泄漏,现场测厚结果表明,弯头缓蚀剂注剂点下方形成一处长150mm、宽100mm的腐蚀减薄区域,最小管壁厚度为2.23mm,且距离泄漏点越近,管壁厚度越小。对腐蚀介质、介质流速、注剂点结构、缓蚀剂、空泡腐蚀等腐蚀影响因素进行了分析,结果表明,在塔顶油气介质腐蚀与冲刷的相互循环作用下,金属管壁不断进行着“腐蚀-生成腐蚀产物膜-腐蚀产物膜受冲刷剥离-漏出的新鲜金属表面继续被腐蚀”的过程,直至腐蚀穿孔。采取降低管线介质流速、更换缓蚀剂等防护措施后,塔顶馏出线弯头部位未再出现腐蚀减薄,腐蚀受到控制,取得了较好的现场防护效果。

Corrosion Leakage Analysis and Prevention of the Bend of the Distill-off Line at Top of Tower of Hydrogenating Unit

Leakage occurred under the injection point of the bend of the distill-off line at top of the main stripping tower of straight run diesel oil hydrogenating unit due to corrosion.The thickness measurement results on the site show that a thinned area of150 mm length and100 mm width due to corrosion was formed under the inhibitor injection point of the bend,the minimum tube wall thickness was2.23 mm,and the closer to the leaking point,the smaller the tube wall thickness.The corrosion influencing factors such as corrosive medium,medium flow speed,structure of injection point,corrosion inhibitor and cavitation corrosion were analyzed.The results show that under the mutual cyclic action of corrosion and erosion of the oil and gas medium at the top of the tower,the metal pipe wall continuously underwent the process of “corrosion- formation of corrosion product film-erosion and liftoff of corrosion product film-leaking fresh metal surface continuing to be corroded” until it was perforated due to corrosion.After protective measures were taken such as reduction of the medium flow speed in the pipeline,and replacement of corrosion inhibitor,thinning phenomenon due to corrosion occurred no more at the location of the bend on the distill-off line at top of the tower,the corrosion was controlled,and better site protection effect was achieved.