Session: Material Selection and Qualification in CCS Downhole Environment (Part II of II)
On the Relative Fitness-For-Service of Alloy 925 Compared to Stainless Steels 22Cr and 25Cr in CCUS Well Completions (C2026-00021)
Thursday, March 19, 2026
4:00 PM - 4:30 PM Central
Location: 342 DE
Earn .5 PDH
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Alloy 925 (UNS N09925) is a well-established Ni-Cr-Mo alloy widely used in completion equipment, offering a minimum yield strength of 110 ksi (758 MPa) along with robust general, localized, and cracking corrosion resistance. Its adoption significantly surpasses that of 22Cr duplex (UNS S32205) and 25Cr super duplex (UNS S32750) stainless steels, despite the latter being more cost-effective and often exhibiting superior localized corrosion resistance in injection environments. For underground CO₂ storage — where trace impurities may lead to acid dropouts — questions arise regarding the comparative corrosion performance of Alloy 925 versus 22Cr and 25Cr. Specifically, concerns focus on both general and localized corrosion resistance, and whether higher-grade Ni-Cr-Mo alloys might be more suitable. This paper (1) revisits the performance of Alloy 925, 22Cr, and 25Cr using eight autoclave tests (70,175,250°F) simulating CCUS impurity conditions (with ppm SO2, NO2, H2S and >300 ppmv H2O), and (2) is complemented by inorganic acid immersion tests. The latter, largely for validation purpose, involved nitric and/or sulfuric acids tests to explore concentration effects and directly compare all three alloys. Results indicate that Alloy 925 exhibits minimal corrosion overall but corrodes slightly more in some diluted acids and less in the presence of H₂S impurities.
