Corrosion Survey of Cooling Water Pipes with Pattern Diagrams of Water Quality

Abstract

This study was performed to investigate corrosion protection of pipe materials used in cooling water systems. The chemical composition of the water affected the corrosion phenomena. The pattern diagrams, such as hexa diagrams and trilinear diagrams, of the major components in the water are well known. In this study, hexa diagrams and trilinear diagrams of the major components (Na⁺, K⁺, Ca²⁺, Mg²⁺, Cl^–, SO₄^2– and HCO₃^–) were drawn based on the results of analysis at each water source, and we investigated the relationships between the corrosion phenomena and the pattern diagrams of the water. The results indicated clear relationships. Water quality can be classified into five patterns according to the pattern diagrams：Ca–Cl or Ca–SO₄ type, Ca–HCO₃ type, Na–Cl type, Na–HCO₃ type, and intermediate type. The water qualities at the two locations of the corrosion survey were classified as Ca–HCO₃ type and intermediate type, and the galvanized steel pipe showed good corrosion resistance in Ca–HCO₃ type. In addition, the results of electrochemical measurements showed that a stable film tended to form on the copper tube in the Ca–HCO₃ type.