Flow-Assisted Corrosion of API 5L X56 Steel: Effect of Flow Velocity and Dissolved Oxygen

Abstract

Flow-accelerated corrosion (FAC) is a complex mechanism of material degradation and depends upon the fluid hydrodynamic parameters, material microstructure and compositions, and environmental chemistry. The effect of flow velocity and dissolved oxygen on FAC behavior of API 5L X56 steels in 0.3 M NaCl solution is investigated. Electrochemical and weight loss measurements were taken in a closed-loop corrosion evaluation system at flow velocities of similar to 0.25, 1.0, 1.6, and 2.3 m/s and dissolved oxygen (DO) contents of similar to 50, 500, 1500, 2500, and 4500 ppb. The corrosion rate observed to increase with flow velocity and dissolved oxygen content. The post-corrosion topography and corrosion products were investigated using 3D profilometry, scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDS), and Raman spectroscopy techniques. The corrosion products mainly contained hematite (alpha-Fe2O3), lepidocrocite (gamma-FeOOH), goethite (alpha-FeOOH), and magnetite ( Fe3O4). The wall shear stress (tau) induced on specimen surface was simulated through CFD approaches and correlated with corrosion resistance of the steel at different flow velocities.