Environmental Limits and Susceptibility of UNS S30403 to Environmentally Assisted Cracking in Thermal Oil Sand Operations

摘要

Environmental and material limits specified in ANSI/NACE MR0175/ISO15156-3:2015 restrict this use of austenitic stainless steel alloys under sour conditions typically encountered in thermal in-situ oil sand operations. This paper is a follow up study to one presented in 2016 (NACE-2016-7892), where C-ring testing was conducted to evaluate the susceptibility of austenitic stainless steels to conditions simulating a severe downhole environment; i.e. 230 °C, pH of 3.5, and variable chloride concentrations and H_2S partial pressures. Prior results indicated that after 720 hours of exposure, material did not show any cracking when tested at 10,000 mg/LCI-and 1,000 kPa pH_2S, and at 50,000 mg/L Cl-and 100 kPa pH_2S. In recent testing, three heats of UNS S30403 were tested under the same environmental conditions above and cracking was observed in some heats, suggesting borderline resistance to cracking under these severe conditions and unsuitability per ANSI/NACE MR0175/ISO15156-3:2015. Additional C-ring testing was performed in a less severe environment consisting of 230 °C, pH of 5, a chloride concentration of 10,000 mg/L and 100 kPa pH_2S, where the same three heats of UNS S30403 demonstrated no cracking.