Modeling Pipeline Corrosion Under a Disbonded Coating Under the Influence of Underneath Flow

Laboratory and field experience revealed an increased corrosion rate of pipeline steel under disbonded coatings when aerated water flows underneath. The quantitative effect of the flow velocity was simulated in this work through mathematical modeling. The simulation included mass transport, fluid flow, and electrochemical reactions. Following analysis of the simulation results, simple algorithms have been developed, which reproduce the detailed modeling results with certain conservatism. The significance of flow velocity and disbondment gap to the corrosion rate is clearly demonstrated in the algorithms. The difficulties confronted with field application of these algorithms are the actual field flow velocity in the disbonded region and the size of the disbondment gap, which cannot be easily known. This velocity, however, can be estimated from groundwater flow velocity in the soil near the disbondment.