Naphthenic Acid Corrosion of Mild Steel in the Presence of Sulfide Scales Formed in Crude Oil Fractions at High Temperature

Increasing demand on the oil market has raised interest in oils with high naphthenic acid (NAP) concentration. These oils were previously considered of lower quality due to their corrosive character. Processing such oils at elevated temperatures encountered in refineries (300-350°C) may cause aggressive corrosive attack on the inside walls of equipment such as pipes and distillation towers. Naphthenic acid corrosion attack is a non-aqueous corrosion process and can be retarded by sulfur containing compounds inherently present in crude oil fractions in the form of soluble sulfides. Although these sulfides can be corrosive as well, they can also form iron sulfide scale on the metal surfaces potentially offering a degree protection against naphthenic acid attack. However the iron sulfide scales can be removed from metal surfaces under the combined effects of high velocity flow and NAP attack. This research project has focused on the role of iron sulfide scales formed in different crude oil fractions on samples made from mild as well as chromium containing steels. They were exposed to naphthenic acid attack under high flow rates at high temperature.