Effects of Carbon Film and Chloride Ions on the Pitting Corrosion of Copper in Anion Exchange-Treated Water Containing Water Treatment Chemicals

Copper tubes are widely used in heat exchangers for air conditioning units and refrigerators. Carbon film formed on the inner surface of copper tubes during manufacturing have been reported to cause carbon-film-dependent pitting corrosion interaction with the quality of the water flowing in the tube. In field applications phosphonic acid (HEDP) and benzotriazole (BTA) are used to suppress this pitting corrosion. Anion exchange-treated water, produced by passing tap water through anion exchange resin to replace corrosive ions (Cl^？ and $S{O}_4^{2？}$ ) with corrosion inhibiting ions ($HC{O}_3^{？}$ ), it has also been reported to improve corrosion resistance when combined with these water treatment chemicals. In this study, the effects of chloride ion concentration and carbon film on the corrosion resistance of copper in anion exchange-treated water containing water treatment chemicals were investigated. Corrosion potential and anodic polarization curves were measured in anion-exchange treated water containing 10 mg/L of HEDP and 5 mg/L of BTA, at various chloride ion concentrations. Copper tube specimens with residual carbon amounts of 0 mg/m² and 5 mg/m² were used. Corrosion potential measurements show that the corrosion potential decreased and corrosion was occurred in the presence of carbon film at a chloride ion concentration of 100 mg/L. Anodic polarization curve measurement showed that the breakdown potential shifted to the less noble potential side as the chloride ion concentration increased. These results indicate that, in anion-exchange-treated water containing water treatment chemicals, corrosion is more likely to occur as the Cl^？ concentration increases. Furthermore, the presence of a carbon film is considered to enhance this tendency.