TWI Technical Literature Review 22953
By Usani Ofem
Duplex stainless steels (DSSs) have been exploited by a wide range of industrial sectors for many years because of their good strength and corrosion resistance. They find application in such sectors as oil and gas, marine, chemical and petrochemical, pulp and paper, and are gradually finding their way into more general transportation and construction. In the oil and gas industry there is an increasing uptake of the use of these steels, particularly where chloride corrosion resistance and toughness are required eg in subsea applications for valves, piping, flow lines, tensioning systems, pumps, separator pressure vessels, etc. Their higher strength and resistance against stress corrosion cracking compared with stainless steel grades such as 304L and 316L gives weight savings which reduces fabrication costs, enabling lighter support structures to be used and a longer life-cycle.
TWI has made pioneering contributions towards research efforts aimed at establishing the influence of key process variables such as heat input and thermal cycles on the microstructure and properties (mechanical and corrosion) of DSS welds, leading to guidelines for formulating welding procedures for DSS. The development of newer grades of DSSs, which has been driven by the need to tailor price to the need of different applications, has brought about additional challenges with the qualification of welding procedures for successful practical fabrication, particularly for the more highly alloyed super duplex grades.