Pressure-induced fatigue failures in cast iron water supply pipes

Abstract

Cast iron pipes have been extensively utilised in water supply networks worldwide. Many of these pipes are either at the onset or within their wear-out phase, during which failure rates rapidly increase, and the pipes should be repaired or replaced. However, the replacement and rehabilitation of these pipes might require extensive resources and time. Therefore, it is essential to investigate the effects of operational practices that might reduce failure rates for ageing cast iron pipes. In this paper, we investigate the conditions under which water pressure fluctuations may impact and accelerate fatigue failures in cast iron pipes. We carried out a systematic review of the mechanical properties of cast iron pipes and conducted sensitivity analyses to estimate fatigue crack propagation using fracture mechanics. Our investigation suggests that cast iron pipes which are affected by reduced wall thickness due to corrosion may experience a significant decrease in their operational life when subjected to water pressure fluctuations. Moreover, this negative influence of pressure fluctuations is exacerbated with an increase in the mean operating pressure. As an example, a 150 mm pipe featuring a corrosion patch of about 7 mm depth could extend its remaining fatigue life by over fourfold through a minor reduction of both mean pressure and pressure fluctuations of approximately 10 mH2O each. The manuscript further explores various pressure reduction combinations and trends, demonstrating the beneficial effects of reducing both mean pressure and pressure fluctuations. Consequently, the presented analysis suggests that water operators should proactively manage (reduce) the magnitude of both pressure components to extend the operating life of ageing cast iron pipes.