Gray cast-iron water pipe metallurgy

The results of a metallographic study of grey cast iron water pipes are reported. These pipes had been installed between 1885 and 1973 in eight different water systems. Each pipe had been extracted during scheduled maintenance or failure repairs to provide data for a larger study to produce a methodology for determining the residual life of grey cast iron pipes. This metallographic study was conducted to determine the causes of variations in the mechanical properties of these pipes. Pit cast and spun cast pipes were found to have distinctly different types of graphite flakes, flake sizes and metallic matrices. These differences were directly responsible for the variations in the mechanical properties between the two types of pipes, with the larger flake sizes of the pit cast pipes in particular producing weaker material. Examples of anomalous pipes that did not have the standard appearance of either type of manufacture were also found and the reasons for their appearance identified. The results of the study show that the metallurgy of the pipes may be a major contributing factor along with external forces such as corrosion or poor installation practices. Metallographic analysis can therefore assist water utilities in making decisions on repairs, rehabilitation and replacement. Corresponding author. E-mail: [email protected]