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.