Electrochemical Analysis of the Pitting Potential of Tin-plated Copper in Artificial Fresh Water Containing Chloride, Sulfate, and Bicarbonate Ions

Tin-plated copper tubes have been widely used in cold and hot water service systems. However, leakage accidents caused by pitting corrosion can occur in such tubes; therefore, it is necessary to evaluate the effects of major environmental factors on the occurrence of local corrosion to ultimately suppress this corrosion. In the present study, the anodic polarization curves of a tin-coated copper electrode were measured in simulated freshwater containing Cl−, SO42−, and HCO3−. The anodic current increased suddenly and sharply due to the breakdown of the passive layer and the initiation and growth of pitting generation at the pitting potential. The pitting potential shifted to a more negative direction with increasing Cl− and SO42− concentrations. In contrast, the pitting potential shifted to more noble potentials upon increasing the HCO3− concentration, indicating that HCO3− has an inhibitory effect on pitting attack by Cl− and SO42−. The quantitative relationship between each anion concentration and the pitting potential was determined by multiple regression analysis. A plot of the pitting potential predicted from the created regression equation and the measured values of the pitting potential showed a positive linear relationship.