The corrosion rates of cast iron and copper in drinkable water distribution systems are compared in this investigation. Sixty-one solutions were prepared, of varying concentrations in Cl-, NO-3, SO=4, and with differences in alkalinity, pH, and Langelier index.
Cut from actual pipe, 2070 specimens 4 cm by 3 cm by 0.1 cm (1035 cast iron and 1035 copper) were immersed in the solutions for 3, 6, 9, 12, or 15 days, and their corrosion was determined by weight loss. For both metals, corrosion was more rapid during the first three days.
The cast iron corrosion product contained between 35% and 55% iron. X-ray diffraction revealed the presence of goethite, lepidocracite, and after three days of immersion, amorphous magnetite.
For the same experimental conditions, the copper corrosion rate was significantly smaller than that of ductile cast iron.
The corrosion rate of copper was not found to be affected by the composition of the water. In this investigation, no correlation was found between the Langelier index and the corrosion rate for copper or cast iron. This was true for both negative and positive Langelier index.