Formation of Multilayer Iron Sulfide Films During High Temperature CO2/H2S Corrosion of Carbon Steel

Abstract

Abstract An experimental programme has been carried out to assess the corrosivity of carbon steel exposed to high-temperature (120°C) chloride-containing brine saturated with CO2 and H2S at H2S/CO2 partial pressure ratios between 0 and 0.6. The experimental work included characterisation of the corrosion product films forming under these conditions. Corrosion experiments were performed in a flow loop at a flow velocity of 10 m/s, corresponding to a wall shear stress of 130 Pa. High general corrosion rates above 30 mm/y without protective film formation were found when H2S was not present under the conditions tested in the experiments. In the H2S/CO2 solutions corrosion product films consisting of several layers of various iron sulfides, and in some cases iron oxide or carbonate layers, were formed. General corrosion rates were 30-40 mm/y at an H2S/CO2 ratio of 0 and about 1 mm/y at H2S/CO2 ratios between 0.2 and 0.6. However, slightly lower steady-state corrosion rates were recorded over time. Pitting corrosion took place at a H2S/CO2 ratio of 0.2.