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COPPER PITTING CORROSION: A CASE STUDY
Citation:
Lytle*, D A. AND M. R. SCHOCK. COPPER PITTING CORROSION: A CASE STUDY. Presented at 2007 WORLD ENVIRONMENTAL AND WATER RESOURCES CONGRESS, Tampa, FL, May 15 - 19, 2007.
Impact/Purpose:
To inform the public.
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. 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.