Soft, Low-Temperature Water-Distribution Corrosion: Yellowknife, NWT

Abstract

Presented are the results of a water-distribution corrosion study conducted for the City of Yellowknife, Northwest Territories, Canada. Conducted were water-distribution system corrosion tests, the evaluation of corrosion inhibitors, and the sampling of the supply water and corrosion tubercles for corrosion-causing and corrosion-intensifying bacteria. Chemical treatment of Yellowknife's soft, poorly buffered, slightly acidic water using chlorine, hydrofluorosilicic acid, and heat during the winter substantially increases its corrosivity. Ductile iron corrosion increased by approximately 40%, moderately reducing its service life. Similarly, copper corrosion increased by 65%, although its service life was not seriously affected. Corrosion inhibitors identified in laboratory immersion tests as possible additives to the city's treated water were sodium hexametaphosphate between the dosages of 1 and 3 mg/L as phosphorus, and the combination of lime and carbon dioxide to produce a water with the tendency to deposit a protective coating of CaCO