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Introduction
According to [2] ASCE (2009), America's drinking water systems received a failing grade of "D- " as it faces an annual shortfall of at least $11 billion to replace aging facilities that are near the end of their useful life and need to comply with existing and future federal water regulations. According to the [3] AWWA (2001), water is the most capital intensive of all utility services, owing to the high cost of pipelines. In addition to being buried underground, where they are "out of sight and out of mind," many pipes were originally installed and paid for by previous generations ([3] AWWA, 2001). As these pipes are aging and nearing the end of their useful life, they need to be replaced; the cost to manage and replace them is becoming our burden.
However, it is not cost-effective to replace a pipe before, or even after, the first break ([3] AWWA, 2001). As such, a proactive approach to pipe asset management is crucial in determining the optimal time to replace a pipe. There are many studies on the prioritization of pipelines for renewal. For instance, [10] Rogers and Grigg (2009) prioritized pipes using a combination of probability models and ranking systems to determine the likelihood of pipe failure. [12] Wood and Lence (2009) applied statistical deterministic equations in order to forecast the number of pipe breaks. [8] Loganathan et al. (2002) determined the optimal replacement time for pipelines by equating the threshold break rate and the predicted break rate. The purpose of this paper is to prioritize pipes at the Honolulu Board of Water Supply (BWS) for replacement based on its expected failure rate, where pipes will be grouped by age and pipe type. The probability of failure for each pipe type will then be computed using the exponential formula for reliability. In addition, the failure rate will be used to forecast the expected number of breaks in 20 years. A comparison is also made between the failure rate and the conditional failure rate of each pipe type by age.
The objective of this paper is to inform the utility manager of the pipe type with the highest probability of failure, thus aiding in the prioritization of pipes for replacement. Also, in understanding...