Pitting corrosion of copper in waters with high pH and low alkalinity

Abstract

Corrosion of copper pipes has been associated with waters with high pH and low alkalinity that also contain significant levels of chloride and sulfate. This study systematically evaluated the effect of pH, alkalinity (or dissolved inorganic carbon [DIC]), orthophosphate, and sulfate on the nature of copper corrosion using a pilot‐scale experimental pipe loop system. Experiments were conducted in the absence of silica, aluminum, or organic carbon, which previously have been linked to pitting corrosion in drinking water systems, and all test waters contained moderate levels of chloride. The study also investigated the effect of chlorine concentration and form of chorine on copper‐pitting corrosion. Results showed that pitting corrosion of copper pipes was reproduced in the pilot‐scale systems after only 91 days of operation. Pitting corrosion occurred in water with low chlorine concentration and DIC and in pH 9 water in the presence of chloride. Pitting was not observed at pH 6.5 and 7 and was evident at pH 8 only when higher chlorine levels were maintained. Sulfate was not necessary to develop pitting corrosion; however, it did affect the composition of the corrosion by‐products