Operational Limits for Austenitic Stainless Steels in H2S-Containing Environments

Abstract This paper describes a series of tests on two grades of stainless steels UNS S31600 (AISI 316) and UNS S66286 (ASTM A453 Gr. 660– Alloy A286) in simulated H2S-contining oil and gas service environments. The purpose of this study was to evaluate these materials for stress corrosion cracking. Triplicate, stressed C-ring specimens of each material were exposed to a 5% NaCl and 0.4% NaCH3COO solution equilibrated with a 1.5 psia (10.3 kPa) H2S at 200 F (93 C), 250 F (121 C) and 300 F (149 C) for 30 days. After exposure, none of the C-rings showed signs of cracking. The UNS S31600 specimens did exhibit pitting after testing at all three temperatures. None of the UNS S66286 (A286) C-rings exhibited pitting after exposure. Following this initial effort, additional tests at 300 F (149 C) were performed consisting of triplicate specimens immersed in three different solutions saturated with 15 psia (103 kPa) H2S: (a) 5% NaCl solution with a pH of 5.5, (b) 16% NaCl solution with a pH of 5.5, and (c) 5% NaCl solution with a pH of 4.5. After these exposures, none of the C-rings immersed in the 5% NaCl solution with a 5.5 pH showed signs of cracking. Two UNS S31600 and one UNS S66286 specimens failed after exposure to the 16% NaCl solution with a pH of 5.5. In addition, one UNS S31600 all three UNS S66286 specimens failed after testing in the 16% NaCl solution with a pH of 4.5. Several of the UNS S31600 specimens exhibited pitting after testing. The maximum pit depth was 10.2 mils (0.26 mm) on a UNS S31600 specimen exposed to the 16% NaCl / pH 5.5 environment. None of the UNS S66286 exhibited pitting after exposure.