Pinhole leaks in copper water lines are a major concern to both homeowners and drinking water utilities because of the high cost of residential line repairs and the waste of water resources from undetected leaks in service lines. Because copper pipe corrosion remains poorly understood, the Environmental Protection Agency (EPA) supports ongoing research to find a remedy for the problem. As part of this effort, scientists at the National Risk Management Research Laboratory (NRMRL) recently identified certain water chemistry combinations that are potentially involved in the growth of pitting corrosion in copper pipes—and potentially useful to water utilities in predicting the effect of water treatment on pitting corrosion. Background Copper is the most widely used material for domestic water supply systems because it is relatively inexpensive and easy to use, abundant in nature, and resistant to permeation by liquids and gasses. Since 1963, over 5.3 million miles of copper plumbing pipe have been installed in about 80 percent of all U.S. buildings. In spite of excellent resistance, copper can be vulnerable to pitting corrosion—and thus to pinhole leaks. The consequences may be very costly. Pinhole leaks in internal pipes in walls or basements may go undetected for long periods, setting up the conditions for mold and mildew to flourish. Leaks may be hard to locate and repair, and may result in higher insurance premiums for homeowners. They are also, of course, a waste of valuable water resources.
Researchers have long known that water chemistry plays a key role in the corrosion and pitting of copper pipes, but research results have not been uniform or conclusive. There have been cases of copper pitting in waters having high pH, low alkalinity, and significant levels of sulfate and chloride. In other cases, aluminum, silica, and other materials have been implicated as the cause of pitting corrosion. The objective of the NRMRL water chemistry study was to systematically investigate the effect of pH, sulfate, alkalinity (inorganic carbon), and orthophosphate on the nature of copper corrosion—localized and uniform. Pilot-scale research was conducted using a recirculating water pipe system located in the EPA's Andrew W. Breidenbach Environmental Research Center in Cincinnati. The system was patterned after previous water chemistry studies for other types of pipe, such as asbestos-cement and galvanized iron, with key modifications for the copper pipe research. Water analyses were performed every two or three weeks to ensure consistency in water quality. In all, 43 experimental runs were completed over several years to evaluate the effect of water chemistry on copper solubility and uniform and localized corrosion. At the completion of the exposure period, various analytical techniques were used to evaluate corrosion effects, including X-ray diffraction and scanning electron microscopy. Research Results to Date
Implications for Water Utilities The results of the study provide supporting evidence to suggest that water utilities can construct relatively simple pilot-scale studies to investigate the tendency of their water to induce pitting and to predict the effect of water treatment. The water quality results of this research show that pitting can be initiated without silica, aluminum, organic carbon, or other variables that have been suggested as being important in pitting or frequently associated with copper plumbing that has failed from pitting corrosion. The paper describing this research recently won the 2009 American Water Works Science & Research Division Best Paper Award. (See Lytle, D.A. and M.R. Schock, (March 2008), "Pitting Corrosion of Copper in High pH and Low Alkalinity Waters," Journal of the AWWA, 100(3):115-128.) Continued research on this study supports NRMRL's Aging Water Infrastructure Research Program. For more information, contact Jane Ice, NRMRL Office of Public Affairs, 513-569-7311.
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