Selecting Cost-Effective Condition Assessment Technologies for High-Consequence Water Mains

Transcription

1 Executive Summary Selecting Cost-Effective Condition Assessment Technologies for High-Consequence Water Mains Project Number: 4553 Date Available: November 2017 Principal Investigators: Balvant Rajani and Yehuda Kleiner, Rajani Consultants Inc. Project Advisory Committee: Dennis Dellow, Essex & Suffolk Water; Jon Kennedy, Tampa Bay Water; Jeff Leighton, City of Portland Water Bureau; and Joseph G. Thurwanger, PE, Aqua America, Inc. Key Findings A comprehensive approach was developed to help utilities make wellsupported rational decisions on when to deploy condition assessment for high consequence water mains, what techniques/technologies to use, and when to stop assessing the pipeline condition and plan for replacement. An inventory of inspection/condition assessment technologies with their associated reliabilities and costs was established. To demonstrate to pipeline owners how to use the approach for their benefit, 15 comprehensive case studies were prepared and described in detail. waterrf.org

2 Background Distribution and transmission networks often account for the lion s share of the total investment in water supply systems. As water mains deteriorate both structurally and functionally, they will reach a point where renewal (replacement or renovation) is necessary. Scarce capital resources available for pipeline renewal make it essential for planners and decision-makers to seek the most cost-effective rehabilitation and renewal strategy, especially for pipes prone to catastrophic failure. Such a strategy will generally seek to: Prioritize pipes and initially focus sufficient resources on those with high consequences of failure Exploit the full extent of the useful life of the individual high-consequence pipes (or groups of pipes) A substantial amount of work has been done in recent years on various aspects of condition assessment and deterioration modeling of high-consequence buried water mains. Despite these efforts, many water utilities and pipeline owners are still not using risk-based condition assessment and decision-making for their high-consequence assets. Because robust inspection and condition assessment of large buried water mains can be an expensive proposition with different methods having wide variances in accuracy (the likelihood that a particular condition assessment technique is expected to identify an impending failure is not widely understood), many practitioners are having difficulty justifying the expense. Practitioners are not sure about how to quantify the expected benefits of this undertaking in a reality of relatively high uncertainties. A decision framework employing a risk-based approach, which is built on a solid foundation of both anticipated failure likelihood and the relative accuracy of various condition assessment techniques, is therefore deemed to have the utmost importance for utilities seeking to employ a rational decision-making process. No less important, when requesting funding allocation for the implementation of inspection and condition assessment in high-consequence pipelines, such a rational decision-making process will provide practitioners with effective means to present a coherent, well-supported business case to senior management and other stakeholders. Objectives The overarching objective of this project was to develop a framework for water utilities through which well-supported rational decisions can be made on when to deploy condition assessment for high-consequence water mains, what techniques/technologies to use, and when to stop assessing pipeline condition and plan for replacement. Specifically, this project: Provides guidance and tools to water utilities on how to determine the cost-effectiveness of applying inspection/condition assessment to a high-consequence pipeline or a group of pipe segments, given available knowledge about their circumstances (e.g., historical performance, environmental and operational conditions, etc.) Deploys risk-based and benefit/cost considerations in a framework to select the most appropriate strategy to determine a cost-effective course of action, including: Preventative renewal/rehabilitation of at-risk pipe segments Selection and implementation of the most appropriate condition assessment technique Determination of when, in the life of the pipeline, inspection/condition assessment is deemed beneficial Scheduling of the next pipeline inspection/condition assessment Estimation of the asset s remaining life and anticipation of complete pipeline replacement Approach The following activities were executed toward accomplishing the project objectives: 2 Condition Assessment Technologies project # Water Research Foundation. ALL RIGHTS RESERVED.

3 A comprehensive literature review was undertaken to understand the state of the knowledge and state of practice related to inspection technologies and risk-based condition assessment and decision-making for highconsequence buried pipes. This literature review included: Methods, models, approaches, strategies, and case studies related to quantifying the likelihood and the consequences (including triple-bottom-line) of pipe failure Failure modes and failure rates of high-consequence pipes, including grey cast iron, ductile iron, PVC, asbestos cement, steel, prestressed concrete cylinder pipe (PCCP), and AWWA C303 bar-wrapped pipe (BWP) A comprehensive approach was developed whereby the entire life cycle cost of a high-consequence pipeline is computed in a probabilistic manner. The impact of pipeline deterioration rate, failure consequence, cost of rehabilitation, accuracy and cost of inspection/condition assessment, cost of emergency repair versus planned intervention, and cost of pipeline replacement are all accounted for in this approach. Consequently, all these factors can be explored and fine-tuned through sensitivity analyses. The approach also includes tools to combine expert-opinion (semi-informative assessment) with hard field data (historical failures, inspection/condition assessment results) into a robust, well-informed assessment of the pipeline deterioration rate. These tools allow pipeline owners to continually update the assessment of pipeline condition based on incoming field data. The approach also allows estimation of the remaining life of the high-consequence pipeline, in anticipation of complete pipe replacement. Pipeline end-of-life is defined as the time at which it is no longer economical to continue repair/rehabilitation, and full replacement is economically preferable. The approach was fully developed as a user-friendly, Excel-based computer program that provides users with immediate access to informed analysis of their high-consequence pipelines. To assist pipeline owners in using the developed approach, an inventory of inspection/condition assessment technologies, with their associated reliabilities and costs, was established. For this inventory development, a comprehensive literature review was undertaken to scan for inspection and condition assessment techniques that are applicable to the various pipe materials, as well as discern probability of detection (POD) and probability of false positives (PFP) for each of these techniques. Inspection/condition assessment technology providers were also consulted to obtain their input as to the reliability of their respective products, as well as the costs of deployment. Users of these technologies were also engaged to discern the full cost (beyond just inspection deployment, e.g., mobilization, preparation, dewatering, etc.) of an inspection session. The inspection technologies database was incorporated into the Excel-based tool. To demonstrate how pipeline owners can use the decision support tool for their benefit, 15 comprehensive case studies were prepared and described in detail. The data for these case studies were obtained from participating water utilities and pipeline owners. The collection of the data involved several communication sessions with each data contributor, by and follow-up by phone. As could realistically be expected, none of the pipeline owners had all the data required to carry out a fully-informed analysis. These data gaps were fully described in the case studies, and corresponding reasonable assumptions were fully described. This made the case studies doubly useful; they not only demonstrated how one might use the decision support tool, but also what one might reasonably do when data are missing or not available. The case studies also demonstrate a useful approach to carrying out sensitivity analyses of the results to uncertainty in the data. Results/Conclusions The main benefit of inspecting high-consequence water mains (pipelines) lies in the potential of the inspection to identify imminent catastrophic failures and prevent them by rehabilitation or replacement of the pipe segment that is about to fail. Pipes deteriorate over time; therefore, the number of imminent failures they experience is expected to rise with age. Consequently, inspection is likely to identify a higher number of imminent pipe segment failures in older pipelines, thus increasing potential savings. Inspection is justified when the value of the expected savings it provides surpasses the cost to implement it Water Research Foundation. ALL RIGHTS RESERVED. project #4553 Condition Assessment Technologies 3

4 It should be emphasized that inspection provides benefits beyond the interception of imminent failures. An additional benefit of inspection is the possible avoidance of premature pipeline replacement, e.g., as a result of an ill-informed reactive decision following a local failure. Inspection also provides a better understanding of pipeline condition. However, these benefits are generally intangible or otherwise difficult to quantify, e.g., premature replacement cannot be adequately quantified without knowing the basis upon which an untimely replacement would be undertaken. This basic premise gives rise to a simple and straightforward basic approach. Firstly, the pipeline deterioration rate and the associated number of expected imminent pipe segment failures must be estimated for every period in the life of the pipeline. Next, the expected number of failures that an inspection might avoid needs to be estimated. The potential cost savings that would result from these failure avoidances can then be estimated. Finally, these potential cost savings need to be compared to the cost of inspection to determine whether there is a good business case to justify the undertaking of inspection at a given point in the time of the pipeline life. The mathematical foundation for the developed approach is fully described and demonstrated, as is the decision process train through which the decision support tool would be effectively engaged. Applications/Recommendations The entire approach was coded into a user-friendly, interactive, and simple-to-use Excel-based application, Pipeline Inspection Decision Analyzer (PIDA). A detailed user s manual was provided, as well as 15 real-life case studies and a database of typical cost ranges and inspection reliability parameters. Municipalities and owners of high-consequence pipelines can use the application immediately to make decisions regarding when to implement inspection/condition assessment and what technology to select among competing ones. In addition, the application can help in determining the benefits expected from carrying out an inspection session, the anticipated pipe segment failure rate and, consequently, the anticipated remaining life of the pipeline. A significant effort was invested in the compilation of the databases for typical costs and reliability parameters of inspection technologies. However, these data are not stationary. Costs change (inflation, competition, technological improvements in pipe material, coating, etc.) and values of inspection technology reliability parameters can vary significantly based on specific experiences and unique conditions. Moreover, these parameter values can also change due to improvements, new technologies, etc. If PIDA or a similar tool is widely accepted as a useful decision support instrument, the industry stands to benefit from establishing a user group that maintains an up-to-date database of related information, such as relevant costs and success rates in applying various inspection/condition assessment technologies (based on which up-to-date reliability parameters for the various inspection technologies could be discerned). Finally, in the course of this research it became clear that although leak detection is a popular and useful means of establishing some aspects of pipeline condition, its consideration within the approach developed here would be rather limited due to its ability to reveal only certain types of pipeline deficiencies. More research is required to extend the proposed approach to leak detection technologies. This research would try to establish the probability of a leak maturing into a full-fledged failure, the probability of a failure to be pre-empted by a leak, probabilistic quantification of the various costs that are associated with leakage, etc. Such understandings would enable the extension of the approach proposed here to include leak detection technologies and compare them to other inspection technologies on an unbiased basis. Multimedia Three Excel-based tools were developed as part of this project: PIDA Framework, PIDA Data Guide, and PIDA Case Studies. A ZIP file containing these tools, along with the User s Manual and a PIDA setup file, is available on the #4553 project page on the WRF website, under Web Tools. 4 Condition Assessment Technologies project # Water Research Foundation. ALL RIGHTS RESERVED.

5 Related WRF Research Best Practices Manual for Prestressed Concrete Cylinder Pipe Condition Assessment, project #4233 Condition Assessment of Large-Diameter Iron Pipe, project #4391 Failure of Prestressed Concrete Cylinder Pipe, project #4034 Financial and Economic Optimization of Water Main Replacement Programs, project #462 Non-Destructive Condition Assessment for Small Diameter Cast and Ductile Iron Pipe, project # Water Research Foundation. ALL RIGHTS RESERVED. project #4553 Condition Assessment Technologies 5