Corrosion Resistance of Sn-58Bi and Sn-65.7Bi-2.3Sb Low-Melting Alloys in Simulated Geological CO2 Sequestration Environments.

This study investigates the temperature-dependent corrosion of bismuth-based low-melting alloys (Sn-58Bi and Sn-65.7Bi-2.3Sb) in simulated geological CO2 storage environments. Experiments were conducted in a high-pressure autoclave, with post-corrosion analysis including gas breakthrough tests, digital microscopy, and XPS. Results show that corrosion depth and rate increase with temperature. When temperature rose from 30 °C to 90 °C, the corrosion-related degradation extent of cement plugs increased from 15.2 mm to 31.6 mm, significantly higher than the increases for Sn-58Bi (0.35 to 0.65 mm) and Sn-65.7Bi-2.3Sb (0.11 to 0.29 mm). The degradation mechanisms of the two types of sealing materials were fundamentally different: class G cement plugs mainly experienced CO2-induced bulk degradation within the cement matrix, resulting in structural deterioration, whereas bismuth-based alloy plugs exhibited limited bulk corrosion and were primarily affected by localized degradation at the alloy-casing interface. XPS identified (BiO)2CO3 as the primary corrosion product. Corrosion impaired sealing integrity: after 90 °C exposure, the breakthrough pressure of cement dropped by 73%, compared to only 2.4% for Sn-58Bi and 0.6% for Sn-65.7Bi-2.3Sb. The study concludes that corrosion accelerates with temperature in CO2-rich environments, and Sn-65.7Bi-2.3Sb exhibits superior corrosion resistance to Sn-58Bi, providing experimental insights into the corrosion resistance and sealing performance evolution of these alloys under simulated CCUS conditions.