Performance Evaluation of Small-Diameter Cast Iron Mains and Their Role in Water Loss

Small-diameter (equal or less than 4-in.) cast iron pipes generally do not have high consequences when they fail. However, many of those old small pipes are leaking or breaking at a much higher rate compared to large diameter mains, due to relatively thinner walls, corrosion, and other factors. In current practice, the risk assessment of water mains relies heavily on main break or leak records to determine the likelihood of failures. However, in many cases, leaks from small-diameter mains seep into the surrounding soil and never come up to the ground surface. This type of leakage could continue for a long time and cause big water loss problems before it is detected and fixed after a leak survey is performed. While conducting leak detection for all small-diameter mains is ideal, it could be cost-prohibitive if the water system is large. It is more practical to evaluate the performance of those small-diameter cast iron mains and replace pipes at the end of their life to avoid or reduce water loss. This paper presents a performance evaluation of small-diameter cast iron water mains using more than 35-year main break data. Field observations from actual pipe failures are conducted to validate the evaluation. Results from leak monitoring for areas with small cast iron mains are used to correlate with findings of the evaluation. The avoided water loss by implementing a proactive management plan for these small cast iron mains is calculated. The findings from this study could provide insights for other utilities with small-diameter cast iron mains.