Performance of Ductile Iron Pipes. II: Sampling Scheme and Inferring the Pipe Condition

Ductile iron (DI) pipes have been used in North America since the late 1950s. This paper describes how understanding gained on the geometry of external corrosion pits is used to devise a sampling scheme and to infer the condition of ductile iron buried water mains. The companion paper describes the exhumation of varying lengths of ductile iron pipes in four North American water utilities. The exhumed pipes were cut into sections, sandblasted, and tagged. Soil samples extracted along the exhumed pipe were also provided. Pipe sections were scanned for external corrosion using a laser scanner to produce corrosion pit data sets. Statistical analyses were performed on geometric properties of corrosion pits such as pit depth, pit area, and pit volume. These analyses were developed further to assess the impact of the different soil characteristics on these pit properties. This paper describes the investigation of appropriate sampling schemes to represent the statistical properties of ductile iron pipe corrosion. With known statistical properties, an approach is developed to infer the condition of the pipe.