Franz Friedl

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

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.

Early Failure Detection Model for Water Mains due to Seasonal Climatic Impacts

Breakage patterns of homogeneous groups of water mains are influenced by non-time-dependent (static) factors, such as material, diameter and vintage and timedependent (dynamic) impact factors, such as soil temperature, soil moisture and changing operating pressure. A steady increase in deterioration is responsible for increasing breakage rates and year-to-year variations of this breakage rates. Some of the year-to-year breakage rates variations among individual mains are a result of irreducible random natural variation (aleatory uncertainty), while some of the variation (epistemic uncertainty) can be explained by the existence of different factors. Partially the breakage rate variations are attributed to climatic impact factors. Hence these seasonal climatic impact factors were examined. The investigations show that yearly breakage rates with above-average failure frequencies are triggered by severe frost periods and are followed by years with reduced failure frequencies as the weak spots were purged due to climatic extremes. Further with an increasing number of previous observed breakages (NOPF) the probability of a pipe to break in freezing periods increases as well. In this paper an early failure detection model due to climatic impact “freezing periods” was derived. The aim of such a model is to identify individual water mains for early failure detection within leakage monitoring programs and further for whole of life cost analyses.

Austrian Activities in Protecting Critical Water Infrastructure

The first section of the chapter gives an overview of the legal rules and standards governing the Austrian water supply sector, but it includes also interdependencies to other sectors. Further, best practices in management and planning established by Austrian utilities and results from an Austrian benchmarking survey for water suppliers are discussed.