Corrosion Behavior of SS304 in Hydrogen Chloride-Containing Environments

The corrosion behavior of stainless steel SS304 was investigated in three major aqueous environments, namely, dry, water-saturated, and free-water conditions, and in two different methanol environments, namely, dry and water-saturated environments with 99% methanol + 1% water. In all the experiments, hydrogen chloride gas was generated through the reaction between sulfuric acid and sodium chloride. An inert carrier gas such as argon then pushed the hydrogen chloride gas to flow over desiccants to make the latter dry. The dry hydrogen chloride gas would then flow into the second flask to which a pre-weighted stainless-steel specimen was exposed at ambient conditions for 48 h. The specimen was retrieved and subjected to surface and chemical analysis using scanning electron microscopy (SEM)/EDAX. The presence of chloride would affirm the adsorption of chloride ions on the metal surface and vice versa. The specimen was then weighted to determine corrosion rate. The results suggested that stainless steel would not corrode in dry hydrogen chloride gas. However, when saturated with moisture, its corrosion rate would increase by about one order of magnitude. In free-water environment, corrosion rate would basically triple. This was because hydrogen chloride gas would react with moisture or water, turning into hydrochloric acid. Being a reducing acid, hydrochloric acid would attack the Cr2O3 layer, leading to general and/or localized corrosion. The presence of methanol seems to have increased the corrosion rate of stainless steels by a factor of three to four.