Failure modes and mechanisms in gray cast iron pipe

Failures in cast iron water mains are more complex and diverse than is widely understood in the industry. This paper discusses the modes and causes of pipe failures that have been encountered during a three year investigation by the National Research Council Canada. In addition to corrosion, manufacturing defects, human error and unexpected levels of pipe loading all play a role in the large number of pipe failures that occur each year. possibly thermal forces due to differences between the temperature of the water in the pipes and the surrounding soil. Another possible loading condition that can cause pipe failures is one produced by soil locking to the pipe wall through friction. Soil movements may then produce tension in the pipe, producing simple tensile failures. Finally, leadite, a sulphur based joint sealing compound used in the 1940s and 1950s appears to produce pipe failures due to the difference between its coefficient of thermal expansion and that of the metal in the pipes it seals. This mechanism is discussed further in Section 3.3