Protecting ductile-iron Water Mains: What protection method works best for what soil condition?

Ductile iron replaced gray cast iron as pipe material in the early 1970s. It has been estimated that almost half of all new water mains installed in North America are ductile iron. The main cause of structural deterioration of all metallic mains is external corrosion, which is induced by environmental and operational conditions. Internal corrosion, on the other hand, can cause significant functional (hydraulic, water quality) deterioration within the distribution system. Methods for external corrosion protection include passive means (coatings or wraps), active means (cathodic protection), or a combination of both. Successes and failures have been reported for the use of various methods under different conditions and circumstances. This article describes the various practices used to protect ductile‐iron mains from corrosion and details case histories that have been reported from around the world. The authors offer some conclusions about the suitability of the various methods to specific circumstances.