Impact of Flow on the Development of Iron Sulfide and Iron Carbonate Layers

Flow is central to the operation of wells and pipelines and can be postulated to govern the formation of protective corrosion product layers, which is critical to overall infrastructure integrity. However, the phenomena involved remain poorly understood. Therefore, the main objective of this work was to investigate the effect of flow on the heterogeneous precipitation of FeS and FeCO₃ as corrosion products on mild steel. Initial corrosion studies were conducted in an autoclave stirred by an impeller. The tests were conducted under quiescent and dynamic conditions for 24 h in an aqueous brine (10 wt.% NaCl, 120°C, 5 bar CO₂, 0 and 10^-3 mol/l Na₂S₂O₃). The experimental results showed that the increase in rotation speed did not prevent the formation of FeS or FeCO₃ crystals. Having confirmed the presence of corrosion product layers, the differences in the trends in corrosion rates may result from the diffusion barrier presented by these layers.

Keywords:
Carbon steel; CO₂; EIS; SEM; XRD; high-temperature corrosion