Corrosion mechanisms of duplex stainless steels in the petrochemical industry

The recent search for new sources of hydrocarbons has led to production from very severe environments which can contain considerable amounts of carbon dioxide, hydrogen sulphide, and chloride ions, combined with temperatures which can exceed 100°C. Oil and gas production from such wells requires highly corrosion-resistant materials. The traditional solution of using carbon steel with additional protection is generally inadequate in these very-aggressive environments. Duplex stainless steels (DSS) are attractive candidates because of their high strength, good general corrosion resistance, excellent resistance to chloride-induced stress corrosion cracking, and good weldability. Although duplex stainless steels have a very good reputation in both subsea and topsides pipework, it is recognized that the tolerance of these materials to variations in microstructure and chemical composition are still not fully understood. The object of this paper is to review the corrosion behaviour of duplex stainless steels in the petrochemical industry, with particular emphasis on microstructures and the effect of changes in chemical composition.