ABSTRACT
Duplex stainless steels are being increasingly used by the oil and gas industry because of their high strength and good corrosion resistance. As new fields are opened up the temperatures and pressures tend to be higher and this calls for increased wall thickness, even with duplex stainless steels. Because of this demand, specifications increasingly require thick sections without realizing what is needed to deliver sound items in these thicknesses. Failure to recognize this results in microstructures containing intermetallic phases (sigma, chi, alpha prime) or nitrides. All of these reduce toughness and corrosion resistance. In addition, they can increase the risk of hydrogen induced stress cracking (HISC) for cathodically protected subsea components. The present paper examines the parameters that control the final structure and how these limit the maximum thickness that is practical. The optimum practices to realize the maximum thickness are discussed and case histories are presented showing both good and bad practice and the technical consequences of the latter.
