The corrosion behaviour of alloy 31 (UNS N08031 - 31 Ni - 27Cr - 6.5Mo - 1.2Cu - 0.2 N - bal. Fe) and other corrosion resistant materials (CRAs) was tested in a wide variety of corrosion tests comprising laboratory and field tests in seawater with and without additions of CO2 and/or H2S, slow strain rate tests, and SSC (sulphide stress corrosion)-tests according to NACE MR0175. Because of its high chromium and molybdenum concentration the critical pitting temperature and
crevice corrosion temperature of alloy 31 are higher than that of UNS N08028 (alloy 28) and UNS N08825 (alloy 825). CCT and CPT temperatures are in the same range as those of nickel base alloys like
UNS N06625 (alloy 625). It is not sensitive to chloride-induced stress corrosion cracking, sulphide- induced stress corrosion cracking or sulphide stress cracking even at high strength levels. UNS N08031
was tested in the cold-worked condition (HRC < 35) for sour gas applications according to NACE TM 0177-96 A and has been approved in NACE MR0175 up to LEVEL VI. The combination of properties makes UNS N08031 a suitable alloy for sour service especially
under conditions, where high strengths, resistance to seawater and resistance to H2S is required. Typical examples would be casings, wirelines, downhole tubing and topside facilities.
Keywords: Pitting corrosion, crevice corrosion, seawater, sour service, stress corrosion cracking, sulphide stress cracking, alloy 31, UNS N08031.