Ensuring Structural Integrity in Subsea Production Systems: Corrosion Simulations for Material Performance Evaluation

Abstract This industrial case study highlights measures that were undertaken to maintain the structural integrity of a subsea tree in the North Sea. The formation water produced along with the hydrocarbons contained more than 220,000 mg/L of chloride ions, rendering the corrosion inhibitor that was used ineffective. For the corrosion inhibitor to be effective, the chloride content could not exceed 135,000 mg/L. To address this issue, seawater, or washwater, was mixed with the production water in a low-alloy steel flowline to lower fluid salinity, enabling the corrosion inhibitor to function. However, this introduced oxygen into the stream, making the washwater corrosive to the low-alloy steel flowline and threatening the integrity of the entire system. Corrosion rate simulations using an industrial prediction tool assessed the corrosion rate of the flowline material under different operating conditions. The corrosion assessment confirmed that the predicted corrosion rates that would be experienced during the designed field life of the flowline were within the acceptable design limits.