Erosion-corrosion interactions of X65 carbon steel in aqueous CO2 environments

When sand is present in carbon dioxide (CO2) corrosion environments in carbon steel oil and gas pipelines, wear rates can be particularly severe. The wear mechanism when surfaces are exposed to impact by a solid-laden corrosive fluid is known as erosion-corrosion and consists of erosion and corrosion components with total erosion-corrosion degradation enhanced by interactions between erosion and corrosion. The causes of corrosion-enhanced erosion and erosion-enhanced corrosion of carbon steel, in this regime, are not fully understood and are the subject of study in this work in a 60 °C, pH 4.7, 2% NaCl solution, containing 1000 mg/L of sand particles with an average diameter of 250 µm, flowing through a submerged impinging jet (SIJ) nozzle at 20 m/s. Particle impact angles and velocities were predicted on the SIJ sample surface using computational fluid dynamics (CFD) to improve the understanding of how particle impingement contributes to erosion-enhanced corrosion and corrosion-enhanced erosion. Corrosion-enhanced erosion accounted for up to 20% of total erosion-corrosion degradation, with focused ion beam scanning electron microscopy (FIB-SEM) analysis showing that removal of work hardened layers and subsurface cracking were causes of enhanced degradation. Erosion-enhanced corrosion was not significant in the conditions tested.