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The Effect of Phosphate on the Morphological and Spectroscopic Properties of Copper Pipes Experiencing Localized Corrosion
WHITE, C. P. AND D. A. LYTLE. The Effect of Phosphate on the Morphological and Spectroscopic Properties of Copper Pipes Experiencing Localized Corrosion. Presented at 2007 WQTC , Charlotte, NC, November 04 - 08, 2007.
To present research information
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. A growing number of problems have been associated with high pH and low alkalinity waters that also contain significant levels of chloride and sulfate. One location in Florida has such a water quality and has been addressing a widespread pinhole leak problem. In recent years, the community initially added orthophosphate to the water and later switched to a blended ortho-poly-phosphate chemical to control the problem. A systematic examination of copper plumbing removed from homes at various stages into chemical treatment would provide useful information regarding the effectiveness of treatment. 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 a Florida test community with time. Pipe sections were examined using a variety of solids analysis techniques including x-ray diffraction, scanning electron microscopy, and energy dispersive spectroscopy. Visual and stereomicroscopic examination of the pipe surfaces did not reveal any obvious changes or impact of phosphate on copper pipe surfaces with time. Pipe surfaces generally were covered or partially covered with a white- to tan-colored uniformly deposited solid. Also, randomly deposed across the pipe surface were mounds of blue- and green-colored corrosion deposits. Images of cross sectional cuts through the mounds showed various degrees of localized corrosion occurring beneath the now appropriately named pit caps. Pits containing dark orange cuprite crystals and the porous floor that separated the cap from the pit were also visible. Examination of the underside of removed pit caps showed that white rings of solid deposits became evident at the base of the blue- and green- colored caps in the region that was in contact with the pipe wall. Scanning electron microscopy and energy dispersive spectroscopy clearly showed the build-up of phosphorous on all areas of the pipe surfaces. In the uniform layer, which was dominantly silicon and copper, phosphorous levels increased from non-detectable to several weight percent with time. Interestingly, with time phosphorous became much more highly concentrated over the pit caps and was present in the white layers at the pit cap base. Phosphorous levels increased from non-detectable to over 10% by weight with time in areas covering and under the pit caps. Clearly phosphorous (as a copper-phosphate compound) was being selectively incorporated into the pit cap and at the base of copper pipe and pit cap. Detailed images and elemental mapping diagrams will be provided to illustrate the conclusions and possible explanations for the observations will be presented.