You are here:
Pitting Corrosion of Copper in Waters with High pH and Low Alkalinity
Citation:
LYTLE, D. A. AND M. R. SCHOCK. Pitting Corrosion of Copper in Waters with High pH and Low Alkalinity. ISSN 1551-8833 , M. Lacey (ed.), JOURNAL OF THE AMERICAN WATER WORKS ASSOCIATION. American Water Works Association, Denver, CO, 100(3):115-128, (2008).
Impact/Purpose:
to share information
Description:
Localized or pitting corrosion of copper pipes used in household drinking-water plumbing is a problem for many water utilities and their customers. Extreme attack can lead to pinhole water leaks that may result in water damage, mold growth, and costly repairs. Water quality has been recognized as the cause of a number of widespread community copper corrosion outbreaks. In particular, there appears to be a growing number of cases associated with high pH and low alkalinity waters that also contain significant levels of chloride and sulfate. The objective of this study was to systematically evaluate the impact 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 have been previously linked to pitting corrosion in drinking water systems and all test waters contained moderate levels of chloride. Also, the impact of chlorine concentration and form added (sodium hypochorite and chlorine gas) on copper pitting corrosion was investigated. 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 waters having low chlorine concentration and DIC (5 and 10 mg C/L, and possibly at 25 mg C/L), and pH 9 water in the presence of chloride. Pitting was not observed at pH 6.5, 7 and was evident at pH 8 only when higher chlorine levels were maintained. In addition, sulfate was not necessary to develop pitting corrosion; however, it did impact the composition of the corrosion by-products associated with pitting corrosion. Increasing the DIC to 50 mg C/L or adding 3 mg PO4/L prevented the initiation of pitting corrosion at pH 9.
