The Corrosion of Superduplex Stainless Steel in Different Types of Seawater

Superduplex stainless steels have been used in seawater systems since 1986 as castings and since 1990 as wrought product.  The performance has been excellent with few problems.  However, seawater is a complex medium and, depending on the redox potential, stainless steels can adopt a wide range of potentials, spanning over a volt.  Different methods of operation can lead to service potentials right across this range and the limits of use for superduplex stainless steel vary according to the potential. They cover the range from stagnant deaerated conditions where microbial activity is high, to chlorinated flowing seawater, where the risk of crevice corrosion is high.  The present paper describes some of the service environments commonly in use and the conditions that give rise to specific operating potentials.  The limits of use under these conditions are described utilizing both laboratory data and service experience.  The results show the ability of superduplex stainless steel to tolerate a wide range of marine service environments without suffering localised corrosion.