Severe localized perforation of a wet-gas pipeline driven by mixed-culture MIC and chloride-accelerated under-deposit pitting in a CO2 environment

Internal localized corrosion in high-salinity wet-gas pipelines poses a severe threat to asset integrity. This study investigates an L245N pipeline that suffered rapid macroscopic perforation at the bottom-of-line position after merely two years of service. A comprehensive methodology integrating ultrasonic mapping, 3D profilometry, SEM-EDS, XRD, and 16S rRNA gene amplicon sequencing was employed to decouple the complex failure mechanisms. Quantitative results reveal an extreme localized pitting rate of 2.32 mm/y, corresponding to a maximum pit depth of 4.64 mm. While the top-of-line was protected by a dense scale comprising 85.7 wt.% FeCO 3 , the bottom-of-line was covered by a highly porous deposit containing 81.7 wt.% CaCO 3 , which facilitated extreme chloride ion sequestration at the metal-scale interface. Concurrently, biological and mineralogical analyses provided direct evidence of microbiologically influenced corrosion (MIC), identifying the enrichment of Desulfovibrio fairfieldensis alongside 5.1 wt.% biogenic FeS within the corrosion pits. Ultimately, the rapid perforation was not driven by standalone factors, but rather a multiplicative synergy of under-deposit CO 2 corrosion, chloride-accelerated autocatalytic pitting, and mixed-culture MIC. This study clarifies how microbial metabolites and halide enrichment disrupt the passivity of FeCO 3 scales, providing critical insights for the integrity management of wet-gas systems.