Influence of Area Ratio and Chloride Concentration on the Galvanic Coupling of Copper and Carbon Steel

Carbon steel (CS) vessels coated with ~3 mm of Cu have been proposed for the permanent disposal of used nuclear fuel in a deep geological repository (DGR) in Canada. In the event of an undetected defect in the Cu coating that exposes the underlying CS to groundwater, the possibility of galvanically accelerated corrosion of CS arises. In this work, the impact of O2 availability, NaCl solution concentration, and cathode:anode area ratio on the galvanic corrosion behavior of Cu/CS couples was evaluated by monitoring the galvanic potential of the couple and the galvanic current passing between Cu and CS. The corrosion products and surface damage were analyzed using Raman spectroscopy and SEM/EDX. Varying the Cu:CS area ratio from 1:1 to 2500:1, the [Cl−] from 0.001 to 3.0 M, the sparging gas from air to Ar, and monitoring the resulting changes in the galvanic current, galvanic potential, corrosion products, and surface damage showed that the galvanic corrosion of CS was most severe when it was exposed to air-sparged solution with a moderate [Cl−] (0.1 M) as part of the couple with the largest Cu:CS area ratio.