According to NACE MR 0175/ISO 15156 standard UNS S31803 duplex stainless steel can be used up to 0.1 bar H2S and 232°C/450°F regardless of the chloride concentration and the pH. These limits based on past studies are very conservative because they do not include any limits of pH and chloride concentrations.
The objective of this paper is to share some recent laboratory data dealing with Sulphide Stress Cracking (SSC) and Stress Corrosion Cracking (SCC) resistance of S31803 above the Standard H2S partial pressure limit. Corrosion resistance of the duplex material was assessed in environments representative of formation waters containing up to 120 g/l chlorides at pH=4.5. Various H2S partial pressures were considered (0.5 to 1 bar) as well as different testing temperatures (24°C/75°F, 90°C/194°F and 150°C/392°F). Constant load tests were performed using specimens coming from three industrial heats.
Results confirmed the strong influence of chloride concentration and temperature on UNS S31803 corrosion resistance. It was also demonstrated that UNS S31803 is resistant to SSC/SCC phenomena up to 0.5 bar H2S under restricted conditions of pH and chloride concentrations which is significantly above NACE MR 0175/ISO 15156 requirements.