Effect of Copper Content of Carbon Steel On Corrosion in Sulfuric Acid

The corrosion rate of carbon steel in 42 percent sulfuric acid solutions has been found to vary considerably between different samples of steel. In an attempt to determine the reason for this variation, an investigation was undertaken in which the effects of chemical composition, microstructure and surface condition of the steel was studied. Results of the investigation indicated that copper content of the steel was the controlling factor determining the corrosion rate. Steels containing 0.02 percent copper had corrosion rates as much as 16 times greater than those of steels containing 0.10 percent copper. Above about 0.10 percent, further increases in copper content up to 0.16 percent did not materially affect corrosion rate. No correlation was found between corrosion rate and any constituent in the steel other than copper. Also, neither condition of the surface nor microstructure of the steel had an appreciable effect on corrosion rate under conditions of the test. Additions of dissolved copper to the test solution appeared to have a slight accelerating effect on corrosion of the steel. Electrochemical measurements indicated that increases in copper content of the steel affected cathodic polarization behavior of the steel in such a way as to reduce the rate of the cathodic reaction in the corrosion process, thereby reducing corrosion rate. It is also possible that copper in the steel has some effect on the anodic reaction; this is being investigated at present.