Laboratory-scale study on the effect of silicate on copper pipe corrosion

Abstract

Silicate in the form of basic silica is used as a copper corrosion inhibitor in drinking water distribution systems. In this work, the effect of silicate on copper pipe corrosion during stagnation was studied. In addition, the effect of silicate and phosphate on copper pipe corrosion was compared. Using a laboratory setup, copper pipe corrosion experiments were performed under controlled pH conditions. Malachite-scaled copper pipes were used for the corrosion experiments. Each experiment was run for 8 h. The addition of silica into water of pH 6.5 and 7.5 increased the initial release of copper (II) ions into water. As the experiments progressed, small amounts of copper (II) ions were removed from solution by precipitation. Dissolved oxygen was consumed during the process. When phosphate was used as corrosion inhibitor, it initially increased copper (II) ions released in water of pH 6.5. In water of pH 7.5, phosphate reduced the leaching of copper (II) ions. When phosphate and silicate were jointly used as corrosion inhibitors, their combined effect was similar to the effect of phosphate. The silica content of water before and after the experiments did not change. Phosphate was removed from water during the process probably by adsorption on the copper pipe surface.