加工高酸原油常减压装置的腐蚀与防护

中石化某企业3.5 Mt/a常减压蒸馏装置加工多种进口高酸原油,平均酸值可达2.0mgKOH/g,在2011年和2012年进行了两次腐蚀检查。检查发现,加工高酸原油后电脱盐困难,造成常压塔顶及其冷凝冷却系统、常顶循系统腐蚀减薄严重;减压塔的减三线及下返塔部位点蚀严重,填料大面积腐蚀散落;316L材质的减压转油线也发生了明显腐蚀。腐蚀分析认为,低温腐蚀主要由原油中的盐水解生成HCl所致,若电脱盐效果差,设备有腐蚀倾向,建议将常压塔顶部筒体和塔盘材质升级为2205,且对塔顶系统必须进行在线监测和定点测厚;316L材质的环烷酸腐蚀有一定的孕育期且和加工原料性质密切相关,因此,装置每次停工都要进行仔细的腐蚀检查,及时掌握腐蚀情况,若有明显腐蚀应将材质升级为317L。

Corrosion and protection of atmospheric-vacuum distillation unit processing high TAN crude oil

A company under SINOPEC processes a variety of imported high TAN crude oils in a 3.5 MM TPY atmospheric - vacuum distillation unit, whose average total acid number （TAN） is up to 2. 0mgKOH/g. The two corrosion investigations conducted in 2011 and 2012 during the shutdown for overhauls found that the electric desalting was very difficult when processing high TAN crude oil, which led to severe corrosion and thinning in overhead, condensing cooling system and overhead circulation system of the atmospheric tower and serious pit corrosion of 3rd side - draw and effluent return location and scattered corrosion of packings of vacuum tower. In addition, the vacuum oil transfer line of 316L stainless steel has also experienced a significant corrosion. The corrosion investigation and analysis concluded that the low -temperature corrosion was mainly caused by HC1 from hydrolysis of salt in crude oil. If electric desalting failed to operate well, the equipment would be corroded. It is suggested to upgrade the materials of cylindrical tower body and trays of atmospheric tower to 2205 steel and apply on - line monitoring and fixed point thickness measurement in tower overhead system. Naphthenic acid corrosion of 316L steel has an incubation stage and which is closely seusitive to the clanging of cvude oil pnperties. Therefore, a detailed corrosion investigation must be made in each shutdown for maintenance to know the corrosion conditions. The material should be upgraded to 317L steel if apparent corrosion is found.