| Erosion-corrosion is an essential threat to the integrity of the oil sand slurry hydrotransport pipes in oil sands industry. In this work, rotating disk electrode technique was used to study the fundamentals of erosion-corrosion of X-65 pipe steel under conditions that are relevant to oil sand slurry hydrotransportation by measurements of potentiodynamic polarization curves and electrochemical impedance spectroscopy. Parametric effects, including electrode rotating speed, temperature, oily phase content, and the sand size and concentration, on erosion-corrosion of X-65 steel were investigated and analyzed. With the increasing electrode rotating speed, the cathodic polarization current increases due to the enhanced oxygen reduction reaction, while the anodic polarization current decreases because of the improved oxidation of the steel. Although the oxygen diffusivity increases with temperature, the resulting oxidation of steel by oxygen is not sufficiently enough to offset the enhanced reactivity of steel at the increasing temperature. The presence of oils is believed to form a layer of oily phase on the steel surface, facilitating the cathodic reduction of oxygen and inhibiting dissolution of the steel. With the increasing sand content and the sand particle size in the solution, the corrosion of the steel is enhanced.;In order to improve the resistance of the pipe steel to erosion-corrosion in oil sand slurry, a Ni-Co-Al2O3 composite coating was fabricated by electrolytic deposition technique on the steel substrate. Potentiodynamic polarization curve and electrochemical impedance spectroscopy measurements show that the deposited coating significantly improves the erosion-corrosion resistance of the steel in water-oil-sand solution that simulates the chemistry of oil sand slurry. The electrodepositing parameters including alumina concentration, cathodic current density, temperature and the electrode rotating speed were studied to determine the optimal conditions for fabrication of the composite coating. The morphology, structure and composition of the coatings were characterized by scanning electron microscopy and energy-dispersive x-ray analysis. The Ni-Co-Al2O3 composite coating develops a compact, uniform, nodular structure with an average thickness of 50 microns. The Al2O 3 amount in the coating increases with the increasing Al2O 3 concentration in electrolyte, which also enhances the co-deposition of Ni and Co. The micro-hardness and wear resistance of the composite coatings are much higher than the steel substrate and increase with the increasing Al2O3 particle content in the coating. |
