AWWA JAW20486

Results are presented of a study conducted to evaluate the importance of several water quality parameters in the corrosion of fresh and aged copper (Cu) and aged zinc (Zn) (galvanized iron) surfaces in low alkalinity waters in Seattle, Washington. Changes in dissolved oxygen, conductivity, and temperature had a moderate effect on the corrosion rate of Cu and Zn, whereas pH and chlorine residual affected Cu but not Zn corrosion rates. Increases in conductivity up to about 200 microsiemens/cm increased Cu corrosion rates significantly but generally had less effect at higher values. Zn corrosion increased with conductivity up to 1000 microsiemens/cm. For equal conductivities, corrosion rates were higher in systems with chloride than in systems with bicarbonate; sulfate had an effect equivalent to chloride on aged Cu and Zn electrodes but equivalent to bicarbonate on fresh Cu. Flow rate had almost no effect on corrosion rates for either metal. Aged and fresh Cu electrodes responded in a qualitatively similar manner to changes in water quality, although different corrosion rates were reached. Fresh Cu, lacking a thick protective oxide film, corroded at a much greater rate than aged Cu. Zinc corrosion rates responded less dramatically to changes in water quality, other than conductivity, than did Cu. The linear polarization technique proved to be a reliable, rapid method for monitoring the changes in corrosion brought about by water quality changes. Includes 5 references, tables, figures.