Performance of corrosion-resistant alloys in concentrated acids

Abstract

Nickel alloys containing optimum amounts of chromium (Cr), molybdenum (Mo) and tungsten (W) are widely used in the chemical processing industries due to their tolerance to both oxidizing and reducing conditions. Unlike stainless steel (SS), Ni-Cr-Mo (W) alloys exhibit remarkably high uniform corrosion resistance in major concentrated acids, like hydrochloric acid (HCl) and sulfuric acid (H2SO4). A higher uniform corrosion resistance of Ni-Cr-Mo (W) alloys, compared to other alloys, in concentrated acids can be attributed to the formation of protective oxide film of Mo and W in reducing acids, and Cr oxide film in oxidizing solutions. The localized corrosion resistance of Ni-Cr-Mo (W) alloys, containing high amount Cr as well as Mo (or Mo + W), is also significantly higher than that of other commercially available alloys. The present study investigates the role of alloying elements, in nickel alloys, to uniform corrosion resistance in concentrated acids (HCl, HCl + oxidizing impurities and H2SO4) and localized corrosion performance in chloride-rich environments using ASTM G-48 test methodology. The corrosion tests were conducted on various alloys, and the results were analyzed using weight loss technique and electrochemical techniques, in conjunction with surface characterization tools.