Evaluating the Economic Residual Life of Water Pipes Using the Proportional Hazards Model |
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Authors: | Suwan Park Chang Log Choi Jeong Hyun Kim Cheol Ho Bae |
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Affiliation: | 1.Department of Civil Engineering,Pusan National University,Busan,South Korea;2.K-water Research Institute,Korea Water Resources Corporation,Daejeon,South Korea |
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Abstract: | This paper provides a method for evaluating the residual lives of water pipes using the proportional hazards model (PHM) based
on the economically optimal replacement times of pipes. The survival times, which are used in the proportional hazards modeling
process, were defined as the economically optimal replacement times of pipes. The break rate of an individual pipe is estimated
using the General Pipe Break Model (GPBM). The optimal replacement time of a pipe is obtained using the equivalence relationship
between the GPBM and threshold break rate. In order to use the GPBM effectively, the process of estimating the GPBM has been
modified in this paper by utilizing additional break data for the time of installation and adjusting the value of the weighting
factor (WF) in the GPBM. The residual lives and hazard ratios of the case study pipes, of which the cumulative number of breaks
was at least one, were estimated using the estimated survivor function of the constructed PHM. The time-dependency of the
pipe material covariate caused the hazard rate of the cast iron pipes to become lower than the hazard rate of the steel pipes
after 19 years since installation. The methodology developed in this paper may help utilities identify important factors related
to the economics of water pipe maintenance and; therefore more efficiently maintain their water pipes. |
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