The Effect of Phosphate on the Properties of Copper Drinking Water Pipes Experiencing Localized Corrosion
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TECHNICAL ARTICLE—PEER-REVIEWED
The Effect of Phosphate on the Properties of Copper Drinking Water Pipes Experiencing Localized Corrosion Darren A. Lytle • Colin P. White
Submitted: 31 December 2013 Ó ASM International 2014
Abstract Extensive localized or pitting corrosion of copper pipes used in household drinking water plumbing can eventually lead to pinhole water leaks that may result in water damage, mold growth, and costly repairs. Water chemistry has been recognized as the cause of some community-wide copper pinhole leak outbreaks. A large drinking water system in Florida recently switched from pH adjustment and orthophosphate addition to a blended orthopolyphosphate chemical to address this problem. The objective of this study was to examine the impact of phosphates on the morphology and elemental composition of the interior surface of failed copper pipes removed from homes in the community. Scanning electron microscopy (SEM) and energy dispersive spectroscopy analysis of pipe surfaces revealed the build-up of phosphorus over time. Phosphorus was most greatly concentrated over areas of localized corrosion attack. Examination of the corrosion by-product mounds that covered corroding pits showed that phosphorus had migrated to the region adjacent to the copper pipe wall. Distinct copper–phosphorus solids were identified under SEM magnification; however, no crystalline copper–phosphate compound was identified by x-ray diffraction analysis.
Electronic supplementary material The online version of this article (doi:10.1007/s11668-014-9786-6) contains supplementary material, which is available to authorized users. D. A. Lytle (&) U.S. Environmental Protection Agency, ORD, NRMRL, WSWRD, 26 West Martin Luther King Dr., Cincinnati, OH 45268, USA e-mail: [email protected] C. P. White Pegasus Technical Services, 46 E. Hollister Street, Cincinnati, OH 45219, USA e-mail: [email protected]
Keywords Copper Pitting corrosion Phosphate Drinking water
Introduction Copper is widely used in home plumbing and distribution system piping material. Although copper is relatively resistant to corrosion, it is not inert and can experience both uniform and non-uniform corrosion in water under certain conditions. Uniform corrosion describes the corrosion of a metal evenly across the surface which often leads to the relatively uniform deposition of corrosion by-products over the pipe surface, while local corrosion results in concentrated areas of corrosion attack. These localized areas of corrosion in copper pipes, also known as ‘‘pitting’’ corrosion, can be a major cause of premise plumbing failure. In relatively short periods of time after copper plumbing installation, copper pitting can occur, and eventually lead to pipe failure in the form of ‘‘pinhole’’ leaks. The cost of plumbing repair and the associated expenses of repairing water-damaged materials can be excessive. Additionally, pinhole leaks may go undetected in walls or basements for months, providing an environment conducive to mildew and mold growth. Pitting
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