Flow-assisted corrosion of X70 steel: Quantifying the interplay of Cl- concentration and hydrodynamics effect in CO2-saturated oilfield water

This study examines the effect of high salt concentration on the flow-assisted corrosion (FAC) behaviour of API 5 L X70 pipeline steel in CO 2 -saturated simulated oilfield water. NaCl concentrations ranging from 0 wt% to 15 wt% were varied at a fixed flow velocity to simulate realistic oilfield conditions. Electrochemical corrosion tests and surface characterisation techniques were employed to assess the corrosion behaviour of the pipeline steel. Results revealed a non-linear relationship between salt concentration and corrosion rate. Initially, increasing the chloride concentration increased corrosion rates, destabilised protective FeCO 3 films, and promoted localised attack. The corrosion rate has peaked at around 5 wt% NaCl. However, further increases to 10 wt% and 15 wt% led to a reduction in the corrosion rate. This decline is attributed to the saturation of corrosive species and the formation of more stable, compact corrosion scales that provide protection under flow conditions. The complex interplay between ionic strength, flow dynamics, and the stability of corrosion products significantly influenced the FAC behaviour. These findings provide valuable insights for predicting corrosion performance and optimising mitigation strategies in saline, CO 2 -rich oilfield environments with varying salinity levels.