Impact of Soil Properties on Pipe Corrosion: Re-Examination of Traditional Conventions

Soil corrosivity is not a directly measurable parameter and pipe corrosion is largely a random phenomenon. The literature is replete with methods and systems that attempts to predict soil corrosivity and resulting metallic pipe corrosion from soil properties (e.g., resistivity, pH, redox potential and others) surrounding the pipe. This paper describes research that endeavors to gain a thorough understanding of the geometry of external corrosion pits and the factors (e.g., soil properties, appurtenances, service connections, etc.) that influence this geometry. This understanding would lead to the ultimate objective of achieving a better ability to assess the remaining life of ductile iron pipes for a given set of circumstances. Varying lengths of ductile iron pipes were exhumed by several North American and Australian water utilities. The exhumed pipes were cut into sections, sandblasted and tagged. Soil samples extracted along the exhumed pipe were also provided. Pipe segments were scanned, using a specially developed laser scanner. Scanned data were processed using specially developed software. Statistical analyses were performed on three geometrical attributes, namely pit depth, pit area and pit volume. Various soil characteristics were investigated for their impact on the geometric properties of the corrosion pits. Preliminary findings indicate that the data not always support traditional conventions.