Incongruous metals, dissimilar soils, different aeration of soil, road de-icing salts, neutral cables installed by electrical utilities, and stray electrical currents from cathodically protected structures such as service station gas tanks are major factors that contribute to the corrosion of ductile iron water mains.
These conditions induce currents between sections of the water main by sacrificing one metal to another in the same way that a dc battery produces current. In a ductile/cast iron water main the material is sacrificed to itself or to copper, brass, or bronze fittings, resulting in pinhole depressions in the ductile/cast pipe surface.
A unique characteristic of cast iron corrosion is that it becomes a composite of cast iron and graphite as the corrosion progresses. This graphite retains the shape of the pipe, camouflaging the true extent of the damage. With the lack of visual corrosion these failures on cast iron have been called "breaks". Often these breaks have been mistaken as being caused by the brittle nature of the cast iron -- not corrosion.
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| 4700 Thickson Road North | Whitby, Ontario -- L1R 2W9 | Phone: 905-655-7122, Fax: 905-655-7178 | Email:info@cp-systems.com |
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