A simple approach to assessing copper pitting corrosion tendencies and developing control strategies

Localized corrosion of copper premise plumbing in drinking water distribution systems can lead to pinhole leaks, which are a growing problem for many homeowners. Despite the fact that water quality is an important factor associated with localized copper corrosion, good approaches for predicting the tendency of water to support localized corrosion and for assessing water treatment options to address problems are not available. The objective of this research was to determine the effectiveness of a simple pipe loop system, installed in a drinking water distribution system, in predicting localized copper corrosion and to assess treatment alternatives in drinking water. Visual examination of the internal surface of copper pipes positioned in the loop revealed signs of localized corrosion (isolated 3 mm diameter mounds of corrosion by-products) after only 72 days. Examination of pipe sections removed from the loops after 101 days clearly showed that localized corrosion was taking place. Cross-section analysis of the pipe showed pits as deep as 0.150 mm that were covered by a thin membrane and a mound of blue-green corrosion products. An ortho- and poly-phosphate blended chemical fed to a second pipe loop, prevented pitting attack, and produced different corrosion by-products. The study showed that simple, inexpensive copper pipe loops can be useful in predicting pitting tendencies of drinking water and in assessing the effectiveness of treatment alternatives.