Dominic Cook, Brendan McAndrew, and Gary Shuker

OBJECTIVES:

The objectives of the project were to (1) collect and analyze information on historic trunk mains failures from research papers and from all U.K. water utilities and thereby develop a clearer understanding of the causal elements that contribute to the failures; (2) build on this improved understanding to develop robust probability and consequence models to be applied to large trunk mains; (3) test the models through application in several company data sets to prove the technique; and (4) develop a framework tool that can be used by utilities.

BACKGROUND:

The failure of large diameter trunk mains, though rare, can be highly disruptive to both water utilities and to the general public. They can have major consequences in terms of public safety, damage to property, interruptions to supply, and have the potential to adversely affect company overall performance assessment (OPA) and company reputation.

APPROACH:

Following an extensive literature review and a U.K. wide expert workshop, water company representatives were asked to complete a data review questionnaire to ascertain the scope and quality of data that might be available for analysis. Based on the responses received, targeted data requests were sent to each company. Ultimately, 13 utilities submitted trunk mains failure data and asset information suitable for analysis.

Following extensive data review and cleansing, a series of regression analyses were carried out in order to derive relationships between failure rates and a range of explanatory factors such as age, diameter, material, and soil type. These analyses were carried out on individual company data sets and on pooled data sets. This process produces a series of expressions for frequency of failure (bursts per kilometer per annum) for all of the common material types. The robustness of these expressions and their transferability from one company data set to another was highly variable. This is considered to be a function of data quality issues and of the varying size of data sets with some of the less common materials producing the least robust expressions.

These expressions provide the failure rate prediction element of the accompanying software tool. In addition, it was necessary to develop an approach to assessing failure consequences for each pipe represented in the model. A simple and flexible approach was adopted allowing utilities to tailor the time and effort expended on this process to suit available resources. The outputs should enable utilities to identify high risk assets and to identify particular consequences contributing to the high risk classification.

RESULTS/FINDINGS:

This project has successfully collected and analyzed information on historic trunk mains failures from research papers and from a significant number of U.K. water utilities in order to develop a clearer understanding of the causal elements that contribute to the failure of large diameter trunk mains. As a result of this process, there is now a better understanding of the typical failure frequencies for commonly used materials and the underlying trends in terms of increases in frequency of failure.

Building on this data, a set of probability and consequence models have been developed that can be applied to large trunk mains. The modeling tool should be appropriate to support utilities in their approach to capital maintenance planning for trunk mains. Data quality was a limiting factor on the robustness of the predictive models. Recognizing this challenge, the project has also produced a trunk mains data protocol, which if adopted, would lead to much improved data quality in the future that in turn would lead to far greater insight into the causal factors of trunk mains failures. It is clearly recognized that the models represent only a first step towards understanding fully the phenomenon of trunk mains failures and particularly the ability to predict long-term trends.

IMPACT:

The model produced as part of this project will be of benefit to water utilities in areas of business planning, continuity planning, strategic asset management, and routine operational management of the trunk mains network. To mitigate the consequences of failure in the most sensitive locations, a monitoring and inspection regime with appropriate contingency plans is recommended. The quality of modeling and trunk mains management in the future could be improved by adoption of the minimum standards of data collection and management set out in the data protocol.

MULTIMEDIA:

The model developed during this project is contained on the CD-ROM accompanying this report. The CD also contains an electronic copy of the Model User Manual and a blank template file necessary for the input of data to the model. A copy of the Model User Manual is also included for reference in Appendix 3 of this report.

RESEARCH PARTNER:

UK Water Industry Research Limited

PARTICIPANTS:

Thirteen utilities submitted trunk mains failure data and asset information suitable for analysis.