In this report the results of a research programme on the criteria which control fracture in cast iron pipes are presented. Experiments were carried out using both new "custom cast" iron pipes and a small number of ex-service pipes. Small scale tests on specimens machined from the pipe wall were used to characterise the materials, whilst full size fracture toughness tests were used to measure the fracture strength of the pipe samples. When old buried iron pipes such as gas mains, fail in service, fractures are frequently found to be associated with through wall notches caused by corrosion. The ex-service pipes showed varying degress of corrosion. It was concluded that fracture mechanics provided a means of assessing the effects of crack like defects in the strength of cast iron pipes. it was found that the main cause of loss of strength in old cast iron pipes was due to the loss of cross-sectional area caused by graphite corrosion but in the cases where the corrosion penetrated the pipe wall then a notch might be generated, causing a loss of strength disproportionate to the loss of section modulus.

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