AWWA WQTC65806

This powerpoint presentation begins by providing background information on pitting corrosion of copper pipes. A case study is presented of a large water utility in Florida that experienced widespread pitting corrosion in copper plumbing. Initially, the community started orthophosphate addition and pH change to mitigate problem in 2003, but switched to 50:50 ortho-polyphosphate blend in September 2005. The objective was to determine how phosphate treatment impacted the surface of copper pipes that were removed from a real distribution system that experienced localized corrosion. Analytical methods included: solids analysis; Scanning Electron Microscopy; morphological and phase contrast; Energy Dispersive Spectroscopy; elemental composition; X-ray Diffraction; and, mineralogy. Results of orthophosphate impact indicated: lack of detection one year into treatment; below EDS detection; carry-out issues; dose consistency; and, accumulation rate. Results of polyphosphate impact and/or orthophosphate impact indicated: measurable increase of P with treatment time; localized concentration of P coating cap; displacement of Si; migration; and, mineral precipitation is possible over time.