Study of AISI/SAE-1020 Steel Corrosion by Sulfidation from Synthetic Sulfur Compounds of Different Molecular Structures

Abstract

In recent years, the petrochemical industry has been affected by the decrease in global reserves of light crude oil, which has led to increase the processing of heavy crude oils with higher concentration of different contaminants that intensify corrosive phenomena. One of corrosion types that occur most frequently in the processing of heavy crude oils is sulfidation, which is caused by organic sulfur compounds of different molecular structures such as: mercaptans, sulfides, disulfides, polysulfides and thiophenes. These organic sulfur compounds are thermally decomposed at operating conditions of atmospheric distillation towers to generate hydrogen sulfide (H2S), which reacts with the steels used in different refinery equipment, resulting in the formation of iron sulfides layers on the material surface. However, morphological properties of the iron sulfides layers formed depend on the molecular structure of the organic sulfur compounds commonly present in heavy crude oils. For this reason, in the present investigation the effect of molecular structure of different sulfur compounds on the morphological properties of corrosion products obtained by the sulfidation of AISI/SAE-1020 steel is determined. The tests are carried out using three different synthetic crude oils (SCO) prepared from a mineral oil matrix mixed with the corresponding sulfur compound: Dimethyl Sulfide, Dimethyl Disulfide and Ethanethiol. The exposure times used for the gravimetric tests were 24, 36, 48, 60 and 72 h at a constant temperature of 300 °C. Discontinuous gravimetric tests are carried out in a batch static autoclave using synthetic crude oils (SCO) with total sulfur content equal to 1 %wt. Morphological characterization of the corrosion products formed on the surface of AISI/SAE-1020 steel was carried out using the techniques Scanning Electron Microscopy (SEM), in combination with Energy-dispersive X-Ray Spectroscopy (EDS), and X-Ray Diffraction (XRD). The effect of the molecular structure of sulfur compounds on the morphological properties of iron sulfides formed on AISI/SAE-1020 steel is of great interest for the petrochemical industry due to the use of a heavy crude oil contaminant for the formation of an organic coating on the steel surface, which can inhibit corrosion by other contaminants present in the crude oil.