Corrosion and Protection Status in Several Chinese Refineries Processing High-Acid Crude Oil

Naphthenic acid corrosion and corrosion protection status in several Chinese refineries processing high-acid crude oil was summarized and analyzed, including material selecting, corrosion monitoring methods, corrosion case. The processing experiences indicate that the most several corroded parts when processing high-acid crude oil occurred in the vacuum column and transfer line. In one refinery, vacuum tower wall, tower packing and transfer line with SS316L (Mo ≥ 2.5 %), were corroded amazing after 3 years operation, which need to be upgraded to SS317L and with the use of corrosion inhibitor to enhance corrosion protection. In another refinery, many high temperature heat exchangers made of carbon steel in the distillation unit were found corrosion severe. In the third refinery, the atmospheric transfer line with SS321 material had a corrosion rate of 0.3 mm/year, found through the fixed-point thickness measurement, and then upgraded to SS316L. From the processing experiences, it could be concluded that selecting SS18-8, SS316L or even SS317L is necessary when processing high-acid crude oil. Corrosion inhibitor is suggested to be used in the most sever corrosion part, for example in the vacuum column and transfer line. Naphthenic acid corrosion of SS316L has an incubation stage. Corrosion is slower in the initial stage, following by a rapid development once the corrosion forming which made the surface of the metal rough. Therefore, every time a unit shutdown, corrosion inspection should be carefully conducted.