Connect, no.79, September 1996
Using results obtained to date from their membership of a two year TWI Group Sponsored Project looking at the corrosion resistance of welded duplex and super duplex stainless steels in sour service, offshore development company Amerada Hess has made considerable savings on both capital investment and lead times for its latest project.
Currently, no reliable data exist for using welds in environments containing hydrogen sulphide (H2S), and materials properties limits set for parent materials are thought to be insufficiently conservative.
The project, now in its second year, investigated two types of duplex (22%Cr) and two types of super duplex (25% Cr) stainless steel using a range of welding processes. In addition, some of the welds tested deliberately contained intermetallic phases which have caused concern with corrosion in the past. Four-point bend tests were performed in autoclaves with differing levels of H2S, chloride and pH.
Initial results show that although super duplex stainless steel is more resistant to severe corrosive media than duplex, for many applications the 22%Cr material is perfectly acceptable.
Following these findings, Amerada Hess substituted duplex stainless steel for super duplex. This saved them money not only by using a cheaper material but also because they were able to receive the material early, rather than wait for the super duplex to be produced. The result was that their operation came on stream earlier than anticipated. Call Paul Woollin for further information on the Group Sponsored Project.