Duplex stainless steel (DSS) has become an increasingly popular alternative to austenitic stainless steel for oil and gas applications due to its superior corrosion and cracking resistance, as well as higher mechanical strength. However, a relatively higher cost over 316/316L stainless steel may prohibit its applications for topside equipment and piping. An alternative solution is the development of lean duplex stainless steel (LDSS) which can provide mechanical properties similar to that of DSS, and is less expensive due to its leaner alloying content. For sour service applications, however, both DSS and LDSS are limited by their susceptibility to sulfide stress cracking (SSC) at low temperatures and stress corrosion cracking (SCC) at elevated temperatures. While several studies have been performed to more clearly define the sour service limits of these materials, beyond those stated in NACE MR0175/ISO 15156, limited data has been generated on welded materials composed of these alloys. The focus of this work was to assess the SSC and SCC susceptibility of DSS and LDSS in chloride-containing sour water conditions. Four-point bend corrosion testing was performed on both parent and gas tungsten arc welding (GTAW) welded UNS S32205 DSS and UNS S32003 LDSS under different H2S concentrations, chloride concentrations, temperatures at a constant CO2 partial pressure. For welded samples, the effects of post-weld surface treatment and passivation on SCC performance were explored. Results of the testing were used to define new sour service limits for parent and welded DSS and LDSS for the given experimental conditions.
Keywords: downloadable, SCC, SSC, duplex stainless steel, lean duplex stainless steel, weldment, sour service