Hydrodynamic Control of Microbiologically Influenced Corrosion at the Sediment–Water Interface in Offshore Marine Environments

Microbiologically influenced corrosion (MIC) represents a significant threat to offshore infrastructure (such as monopile) operating in the mud zone. The sediment–water interface creates an aggressive environment, where steel structures are in direct contact with sediment, and oxygen availability is limited, creating conditions favorable for anaerobic microbial activity and MIC. At the same time, near-bed hydrodynamic conditions in offshore environments are inherently heterogeneous, even within nominally laminar regimes. However, despite this variability, a mechanistic understanding of how small changes in near-bed flow modulate biofilm development, mass transport, and dominant MIC mechanisms remain limited. Here, we investigated the role of controlled laminar hydrodynamics under anoxic sediment–water interface conditions relevant to offshore wind monopiles. Carbon steel coupons were exposed in a column system inoculated with the North Sea sediment communities. Corrosion rates and pit morphology were quantified by gravimetry and three-dimensional surface profilometry, while microbial community composition (16S rRNA gene sequencing), dissolved sulfide, and untargeted metabolomics resolved the governing biogeochemical processes. The result indicated that static (no flow) conditions promoted diffusion-limited biofilms dominated by sulfate-reducing bacteria (SRB) and acetogens, resulting in low and relatively uniform corrosion. Low laminar flow conditions enhanced syntrophic interactions and sulfide accumulation, producing moderate corrosion severity. In contrast, higher laminar flow reduced bulk sulfide accumulation and biofilm thickness yet generated the most pronounced pitting rate. These findings demonstrate that MIC cannot be confirmed or excluded based solely on sulfide concentration, microbial presence, etc. Rather, corrosion emerges from the coupled interplay between hydrodynamics, biofilm architecture, mass transport, and electrochemical surface processes.