Estimating the Timing of the Economical Replacement of Water Mains Based on the Predicted Pipe Break Times Using the Proportional Hazards Models

Deteriorated water mains fail frequently causing service disruption and other inconvenience to the customers. Therefore, the utilities must conduct repair, rehabilitation and/or replacement in a timely manner to satisfy the needs of the customers. To succeed in this process the utilities must also consider the economics of the water main maintenance. The proposed methodology presents not only a method for the optimal maintenance but also a practical way of conducting it by providing the economical time period of maintenance. A method is also presented for analyzing the accuracy of proportional hazards models (PHMs) in forecasting break times and estimating the timing for economical replacement of water mains. A survival probability criterion for the forecasting of the pipe breaks was determined in order to minimize the prediction errors of the PHMs. Subsequently, the criterion was used to estimate the upper and lower bounds of future break times of a water main using the survival functions derived from the PHMs. Two General Pipe Break Prediction Models (GPBMs) for a pipe were estimated for each of the two series of the recorded and predicted, upper and lower bound break times. The threshold break rate (TBR) was coupled with the two GPBMs for each pipe and solved for time to give the upper and lower bounds of the economical replacement time period.