Abstract
Traditionally copper alloys, such as gunmetals and nickel aluminium bronzes, have been used for seawater cooling and firewater pumps. The drawbacks to these copper alloys are their susceptibility to erosion corrosion at high water velocities and to pitting in polluted waters containing sulphides. Austenitic cast iron pump cases have suffered from SCC (stress corrosion cracking ) problems after 1 to 6 years in warm seawater. However, with the development of AOD (argon oxygen decarburization) melting and the use of nitrogen as an alloying element, cast stainless steels offered a viable alternative. These alloys do not have the velocity restrictions of copper alloys, and also have excellent resistance to sulphide in polluted water. The present paper describes the available cast austenitic and duplex stainless steel grades and discusses both their castability and corrosion resistance. The conclusion is that superduplex stainless steel offers the best combination of properties for this application. Some case histories are presented showing the successful use of superduplex and problems arising with other stainless steel grades.
