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A Summary of the Findings of Recent Watermain Corrosion Studies in Ontario

Published: 19910101 by Corrosion Service Company Limited
Author(s): Robert Wakelin

This paper provides a summary of the statistical findings of several recent watermain corrosion studies conducted for municipalities in Southern Ontario. External corrosion rates are correlated with soil resistivity, chloride ion concentrations, pH, watermain material, and galvanic factors. Internal corrosion rates are correlated with watermain age and diameter, and are compared to external corrosion rates. Case studies of watermain failure histories are also presented for three municipalities.

The paper shows that where copper service piping is used, soil resistivity is the only soil characteristic which has a significant effect on the external corrosion rates. The corrosion rates of watermains connected to lead, galvanized iron, or ductile iron service piping, on the other hand, are found to be relatively independent of soil characteristics. Failure rates of inn watermains connected to lead or iron service piping are found to be consistently lower than those associated with copper service piping.

Internal corrosion rates are found to decrease exponentially with time, with large diameter mains generally exhibiting higher rates than small diameter mains, but the amount of internal surface area pitted is found to increase with time. Internal corrosion is found to result in a greater total loss of metal than external corrosion, but maximum internal pit penetration rates are limited to values much less than the maximum external rates.