This study included stirred autoclave tests to broaden the understanding of the interaction between sulfide films and naphthenic acids, and Hot Oil Flow Loop (HOFL) experiments that provided information on the influence of flow on the corrosion process. A series of parametric tests were conducted in an ultra low sulfur, hydrotreated base oil with additions of high purity reagent grade naphthenic acid. Naphthenic acid corrosion was produced at TAN levels of 1.5 mg KOH/g and higher. The limiting TAN was dependent on magnitude of the mechanical forces produced by the flowing oil (i.e. higher limiting TAN values associated with lower flow
velocities). The relative naphthenic acid corrosion resistance of 5Cr-0.5Mo (5Cr) and 9Cr-lMo (9Cr) steels were only marginally different. The studies also showed that naphthenic acid corrosion could be successfully inhibited on two materials (5Cr and 9Cr steels) by the presence of moderate levels of H2S. However, this phenomenon was limited by resistance of the material to velocity accelerated sulfidic corrosion at higher levels of H2S and wall shear stress. Selective
studies of the influence of other sulfur species on naphthenic acid corrosion were conducted. It was found that successful inhibition of naphthenic acid corrosion was only achieved when intermediate levels of H2S were present in the off-gas either from direct H2S loading or from
thermal decomposition of the sulfur species.
Keywords: Naphthenic acid, petroleum, refining, TAN, Total Acid Number, hydrogen sulfide, inhibition, research, test