On the Serviceability of Well Completion Stainless Steels in Moist CO2 Gases with Trace Impurities

Abstract Due to the lack of operational CCS metallurgy guidelines for corrosion-resistant alloys (CRA), particularly stainless steels for well completions, the performance of several of the latter alloys has been evaluated by pressure – temperature cycling with periodic trace impurity replenishment. Material testing was completed between 70°F (21°C) and 250°F (121°C) with pressures up to 4000 psi (275 bar) using 3-to-5 multiday cycles for over 35 days. The corrosion-resistant alloys (CRA) under test included 13Cr (UNS S42000), S13Cr (UNS S41425), 15Cr (proprietary), 17Cr (proprietary), 22Cr (UNS S31803), and 25Cr (UNS S32750). Two widely different CO2 compositions were selected and further examined by OLI (ver. 11.5) thermodynamic calculations to explain the corrosion test results. This investigation confirms a general relationship between CRA composition and corrosion resistance, particularly Pitting Resitance Equivalent Number (PREN), discusses in-situ chemical interactions and the role of water and sulfur species on corrosion, and generally concludes with much narrower operational ranges for martensitic and super-martensitic stainless steels. This work also emphasizes the importance of prolonged tests with impurity replenishments and the need for reliable simulation tools to explain and correlate corrosion and environmental data.