The corrosion behavior of a novel 17Cr3Mn2Ni2Mo triplex stainless steel in ultra‑deep offshore carbon storage formation environment

The corrosion behavior of a novel 17Cr3Mn2Ni2Mo triplex stainless steel was investigated under varying CO₂ partial pressures at 200 °C, simulating ultra‑deep offshore carbon capture, utilization and storage (CCUS) downhole environments in the western South China Sea. High‑temperature, high‑pressure exposure tests combined with comprehensive surface analysis were employed to elucidate the corrosion mechanisms of its constituent phases, martensite, austenite, and ferrite, in an aggressive CO₂–Cl⁻ environment (25,000 ppm Cl⁻). Results indicate distinct phase‑dependent corrosion responses: martensite exhibited the highest susceptibility, followed by austenite, whereas ferrite remained nearly immune. Surface characterization and thermodynamic calculations revealed the formation and evolution of multiphase corrosion products, which play a critical role in governing long‑term stability and corrosion kinetics. This study provides new insights into the corrosion evolution of triplex stainless steels and establishes a fundamental basis for optimizing their microstructure for high‑temperature, high‑pressure CO 2 service. The 17Cr3Mn2Ni2Mo steel demonstrates promising potential as a candidate material for ultra‑deep well tubing and CCUS infrastructure with enhanced corrosion resistance and mechanical reliability.