O 2 -CO 2 -MIC synergistic corrosion failure of a natural-gas pipeline: Mechanism and sulfide generation under low-SRB conditions

An L290 natural gas pipeline failure in an N 2 -flooded field (0.32–1.5 mol% CO 2 , 0.29–1.48 mol% O 2 ) was investigated through field examination, experimental characterization and numerical simulation. Field examination revealed 6 o’clock through-wall perforation, a ∼20 cm 9 o’clock longitudinal groove, and 2.2 cm porous scale with tubercles. Notably, energy-dispersive X-ray spectroscopy (EDS) mapping detected sulfide at all clock positions. X-ray diffraction (XRD) identified FeCO 3 , Fe 2 O 3 , FeOOH, and FeS in both outer and metal-contacting layers, indicating active Sulfate-reducing bacteria (SRB) colonisation, despite negligible planktonic SRB (6–60 cells/mL) and undetectable H 2 S—two standard indicators for low MIC risk. This demonstrates that metal-surface biofilm communities, not planktonic populations, govern MIC severity, challenging conventional monitoring strategies. Laboratory corrosion test at 25 °C, 2.5 MPa replicated sulfide by EDS and pitting via scanning electron microscopy (SEM), while FLUENT and OLGA simulations proved persistent liquid holdup concentrated at the failure zone due to pipeline elevation effects. Synergistic microbiologically influenced corrosion (MIC), CO 2 and O 2 corrosion was confirmed as the root failure mechanism. This study advocates surface bacterial detection, optimized N 2 flooding for O 2 control, and seasonally-adjusted pigging to avoid corrosion failures, providing practical references for professionals working on gathering gas pipeline corrosion management, and MIC risk prediction.