Stress corrosion cracking behavior and mechanism of stainless steel coiled tubing served for CO₂ flooding injection well in CCUS-EOR environments

Stress corrosion cracking (SCC) behavior and mechanism of stainless steel coiled tubing in CO₂ injection wells were investigated through comprehensive analysis. The research demonstrates that at elevated temperatures, the defect concentration within the passive film on the weld and heat-affected zone (HAZ) surfaces increases, while the reduced ratios of Cr_ox/Cr_hy, Fe_ox³⁺/Fe_ox²⁺, and O^2–/OH^– degrade the stability and pitting resistance of passive film. High concentrations of Cl^– promote the preferential localized dissolution of the passive film on the weld surface, triggering the initiation of pitting corrosion. Under high residual stresses at weld surface, microcracks preferentially nucleate at the bottom of corrosion pits in the weld and HAZ. These cracks propagate along deformation bands, twins, and dislocations regions with high defect concentrations via a mixed intergranular and transgranular SCC mode. Sulfide enrichment at crack tips further drives crack propagation. Ultimately, cracks propagate from the inner to outer wall of coiled tubing, culminating in structural failure.