Failure analysis of localised corrosion at 28 Cr32Ni (Alloy 28) tubing in a sour gas well prompted systematic investigations on the performance of relevant corrosion resistant alloys (CRA) in synthetic high salinity brines at high H2S partial pressures in the absence and presence of elemental sulfur at 130° to 180°C. The CRAS included superaustenitic steels, nickel and nickel-cobalt base alloys and titanium alloys. CRAS with pitting resistance equivalents (PRE)of 39 and lower (including 28 Cr32Ni) suffered in unbuffered brines from pitting and crevice corrosion already at 130°C. Alloy C276 and Ti Beta-C alloys proved complete resistance in all media tested up to 180° C. The effect of medium composition on CRA performance was studied at 130°C with respect to the presence of elemental sulfur, H2S, iron sulfide, and CaCO3 in NaCl/CaCl2 brines with a total of 160 g/l chloride.
Keywords: Sour gas, gas well, corrosion. resistant alloys, austenitic steels, nickel base alloys, nickel-cobalt base alloy, titanium alloys, hydrogen sulfide, elemental sulfur, brine, sodium chloride, calcium chloride, calcium carbonate, buffer, iron sulfides.