Mechanism of electrochemical corrosion of steel under water drop

A home-made micro-electrode technique was used to investigate electrochemical corrosion of steel under a chloride-containing water drop, simulating the corrosion scenario encountered in pipelines transporting diluted bitumen. Potential and potentiodynamic polarization curve measurements were conducted at both edge and the centre of the water drop. Morphological and topographic characterization was performed by an optical microscopy and scanning Kelvin probe. Results demonstrated that corrosion of steel under water drop occurs with separated cathodic and anodic reaction regions. While the anodic reaction primarily occurs at the centre of the water drop, the cathodic reaction occurs dominantly at the water edge. Corrosion product is formed and deposited in between, shown as a typical corrosion product ring.