Failure Propagation for Large-Diameter Transmission Water Mains Using Dynamic Failure Risk Index

Abstract

Large-diameter transmission water mains (LDTWM) are lifelines of water supply systems and normally have low failure rates. In Austria the state of the art in condition assessment of LDTWM is to document after a failure and subsequent repair, a routine maintenance or a replacement of valves and accessories. Costs and impacts generated by LDTWM-failures require the necessity to understand the occurrence-probability of failure modes and the associated consequences. Additionally little work has been done on making desirable decisions prior to water main failures. The amount of water losses is one influencing parameter on LDTWM failure costs. Therefore global sensitivity analyses for specific failure modes were executed to define the most sensitive input-parameters on the amount of water losses per break. For 5 Austrian water utilities failure mode statistics have been analyzed on availability, reliability and completeness. A risk assessment methodology, a definition of relevant factors causing specific failure modes responsible for water losses and the use of bivariate logistic regression analyses to derive the main influencing factors on the occurrence of these failure modes are presented in this paper. Furthermore a vulnerability analysis which is used to quantify hydraulic driven consequences of specific failure modes is described. This paper aims to define high risk LDTWM to be prioritized for inspection, repair or rehabilitation. The methods were applied to one Austrian water utility and for 5 different failure modes.