Effect of Chloride Ion on Metal Corrosion Behavior under Pinhole Defect of Coating Studied by WBE Technology

Array electrode (i.e., wire beam electrode, WBE) technique was used to study the effect of chloride ion on the corrosion behavior of metal under the coating with pinhole defects. The results show that WBE technology could characterize the surface current of material. Under the condition of pinhole defects in the coating, the anode region of the corroded galvanic cell first appeared at the pinhole defect, and the cathode region gradually expanded around it. In distilled water, corrosion was stagnant due to the coverage of rust layer. With the increase of the concentration of chloride ions in the solution, the corrosion stagnation phenomenon was eliminated, both the corrosion rate and the cathode migration rate were accelerated. Under the condition of pinhole defect, the anode area would move from the defect position to the area around the damage position, and the cathodic current might occur along the damaged position.