Orientation-dependent SRB biofilm adhesion and formation on carbon steel in injection water environments

This study explores the orientation-dependent behaviour of microbially influenced corrosion (MIC) in carbon steel pipelines exposed to injection water environments. API 5L X52 carbon steel coupons were positioned at 6, 9, and 12 o’clock orientations to simulate operational conditions and analyzed using electrochemical impedance spectroscopy (EIS), gravimetric analysis, scanning electron microscopy and energy-dispersive X-ray spectroscopy, and sessile cell quantification. The 6 o’clock orientation exhibited the most severe corrosion, with a maximum rate of 0.54 mm/year, correlating with the highest sessile cell density ((1.5 ± 0.3) × 10⁷ cells/cm²), extensive biofilm colonisation, and significant weight loss. Intermediate degradation occurred at 9 o’clock (0.26 mm/year), while the 12 o’clock orientation showed the lowest MIC activity (0.15 mm/year). Gravimetric and EIS results demonstrated strong agreement, with lower charge transfer resistance (Rct) values aligning with higher mass loss. SEM and EDS analyses confirmed the presence of mature biofilms and corrosion products including iron oxides and sulphides. These findings emphasise the critical influence of gravity-induced sedimentation, nutrient accumulation, and reduced shear forces in enhancing MIC at the 6 o’clock position.