Models for Prediction of Long-Term Corrosion of Cast Iron Water Mains

Corrosion of cast iron pipes buried in wet soils has long been associated with severe localized effects often attributed to microbiological influences and also with the chemical and physical properties of the soils. Despite more than 70 y of research effort, correlations have remained poor. Recently, the reasons for this have been elucidated, as reviewed briefly herein. Also, interpretation of data from actual cast iron pipes buried in a variety of soils for up to 129 y shows that two critical factors governing depth of local corrosion penetration are the type of soil and the compaction of that soil around the pipe. The latter influences the size of wet air-voids in the soil at the pipe surface. These cause differential aeration and associated severe localized corrosion. The other critical factor is the time of wetness of the soil/metal interface. This is related both to atmospheric precipitation (e.g., rain) and to soil permeability as governed by compaction. Microbiological corrosion has no influence unless essential nutrients continue to be available. These new views on an old subject permit the development of corrosion penetration models for longer-term corrosion.