The Effect of Anion-Exchange-Treated Water Containing Phosphonic Acid and Benzotriazole on Copper Corrosion Resistance

Copper tubes have high thermal conductivity, excellent workability, and corrosion resistance. For these reasons, they are widely used in air conditioning equipment. However, copper tubes can corrode due to interactions between the material and its environment. The carbon film-dependent pitting corrosion is caused by the relationship between the carbon film on the inner surface of copper tubes and the quality of the water flowing them. Phosphonic acid (HEDP) and benzotriazole (BTA) have been reported to suppress pitting corrosion. Additionally, it has been reported that water quality components such as calcium ions (Ca²⁺), silicate ions (${\text{SiO}}_4^{4?}$ ) and bicarbonate ions (${\text{HCO}}_3^{?}$ ) are effective. Tap water contains various ions, including chloride ion (Cl^?), sulphate ion (${\text{SiO}}_4^{2?}$ ) and bicarbonate ions (${\text{HCO}}_3^{?}$ ). Cl^? and ${\text{SiO}}_4^{2?}$ are known as corrosive ions. Conversely, ${\text{HCO}}_3^{?}$ is known as corrosion-inhibiting ions. Anion-exchange treatment is a technology for reducing corrosive ions in tap water. It has been reported that anion-exchange treated water inhibits corrosion in carbon steel pipes used within the same system as copper tubes. However, there are few reports on its corrosion-inhibiting effect on copper tubes. This study focused on the effect of anion-exchange treated water on copper pitting corrosion. The test specimens used different amounts of carbon film. The test solution