Best Practices Manual for Prestressed Concrete Cylinder Pipe ...

Best Practices Manual for Prestressed Concrete Pipe Condition Assessment: What Works? What Doesn’t? What’s Next?

Subject Area: Infrastructure

Best Practices Manual for Prestressed Concrete Pipe Condition Assessment: What Works? What Doesn’t? What’s Next?

©2012 Water Research Foundation. ALL RIGHTS RESERVED.

About the Water Research Foundation The Water Research Foundation is a member-supported, international, 501(c)3 nonprofit organization that sponsors research that enables water utilities, public health agencies, and other professionals to provide safe and affordable drinking water to consumers. The Foundation’s mission is to advance the science of water to improve the quality of life. To achieve this mission, the Foundation sponsors studies on all aspects of drinking water, including resources, treatment, and distribution. Nearly 1,000 water utilities, consulting firms, and manufacturers in North America and abroad contribute subscription payments to support the Foundation’s work. Additional funding comes from collaborative partnerships with other national and international organizations and the U.S. federal government, allowing for resources to be leveraged, expertise to be shared, and broad-based knowledge to be developed and disseminated. From its headquarters in Denver, Colorado, the Foundation’s staff directs and supports the efforts of more than 800 volunteers who serve on the board of trustees and various committees. These volunteers represent many facets of the water industry, and contribute their expertise to select and monitor research studies that benefit the entire drinking water community. Research results are disseminated through a number of channels, including reports, the Website, Webcasts, workshops, and periodicals. The Foundation serves as a cooperative program providing subscribers the opportunity to pool their resources and build upon each others’ expertise. By applying Foundation research findings, subscribers can save substantial costs and stay on the leading edge of drinking water science and technology. Since its inception, the Foundation has supplied the water community with more than $460 million in applied research value. More information about the Foundation and how to become a subscriber is available at www.WaterRF.org.


Best Practices Manual for Prestressed Concrete Pipe Condition Assessment: What Works? What Doesn’t? What’s Next? Prepared by: Mehdi S. Zarghamee, Rasko P. Ojdrovic, and Peter D. Nardini Simpson Gumpertz & Heger Inc., 41 Seyon Street, Bldg 1, Suite 500, Waltham, MA 02453

Jointly sponsored by: Water Research Foundation 6666 West Quincy Avenue, Denver, CO 80235 and U.S. Environmental Protection Agency Washington D.C.

Published by:


DISCLAIMER This study was jointly funded by the Water Research Foundation (Foundation) and the U.S. Environmental Protection Agency (EPA) under Cooperative Agreement No. EM-83406801-1. The Foundation and EPA assume no responsibility for the content of the research study reported in this publication or for the opinions or statements of fact expressed in the report. The mention of trade names for commercial products does not represent or imply the approval or endorsement of the Foundation or EPA. This report is presented solely for informational purposes.

Copyright © 2012 By Water Research Foundation ALL RIGHTS RESERVED. No part of this publication may be copied, reproduced or otherwise utilized without permission. ISBN 978-1-60573-169-8 Printed in the U.S.A.


CONTENTS

LIST OF TABLES ......................................................................................................................... ix LIST OF FIGURES ....................................................................................................................... xi FOREWORD ............................................................................................................................. xiii ACKNOWLEDGMENTS .............................................................................................................xv EXECUTIVE SUMMARY ........................................................................................................ xvii CHAPTER 1: INTRODUCTION ....................................................................................................1 Purpose of the Project and the Manual ............................................................................... 1 Scope ................................................................................................................................... 1 Method of Approach of Investigation ................................................................................. 1 Background Data ................................................................................................................ 2 PCCP Performance History ................................................................................................ 4 PCCP Failure Modes........................................................................................................... 5 Causes of PCCP Failure ...................................................................................................... 5 Design deficiency.................................................................................................... 5 Manufacturing deficiency ....................................................................................... 6 Installation deficiency ............................................................................................. 6 Adverse environment .............................................................................................. 6 Operation................................................................................................................. 6 CHAPTER 2: RISK AND ASSET MANAGEMENT ....................................................................7 Failure Risk Analysis .......................................................................................................... 7 Asset Management Process..................................................................................... 7 CHAPTER 3: SUMMARY OF TECHNOLOGIES ......................................................................13 Condition Assessment Technologies ................................................................................ 14 Internal Visual Inspection .................................................................................... 14 External Inspection of Pipe Surface ...................................................................... 14 Leak Detection ...................................................................................................... 16 Advanced NDT Technologies for Condition Assessment .................................... 17 Over-the-line Corrosivity and Corrosion Surveys ................................................ 18 Monitoring Technologies .................................................................................................. 19 Periodic Inspection ............................................................................................... 20 Advanced NDT Technologies for Monitoring ...................................................... 20 Uncertainties in NDT Technologies ................................................................................. 20 Failure Margin Analysis Methods .................................................................................... 26 Failure Margin Analysis Using Risk Curves Technology .................................... 26 Risk Ranking ......................................................................................................... 27 Neural Network ..................................................................................................... 28

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vi | Best Practices Manual: Prestressed Concrete Cylinder Pipe Condition Assessment

Fuzzy Markov Approach ...................................................................................... 28 Cost ................................................................................................................................... 29 CHAPTER 4: CONDITION ASSESSMENT TECHNOLOGIES ................................................31 Internal Inspection ............................................................................................................ 31 Description ............................................................................................................ 31 Application ............................................................................................................ 34 Internal Visual Inspection Summary .................................................................... 35 External Inspection of Pipe Surface .................................................................................. 36 Description ............................................................................................................ 36 Application ............................................................................................................ 42 External Inspection of Pipe Surface Summary ..................................................... 43 Leak Detection .................................................................................................................. 44 Description ............................................................................................................ 44 Application ............................................................................................................ 48 Leak Detection Summary ..................................................................................... 49 Electromagnetic Inspection ............................................................................................... 50 Description ............................................................................................................ 50 Application ............................................................................................................ 53 Electromagnetic Evaluation Summary ................................................................. 57 Stress Wave Analysis ........................................................................................................ 58 Description ............................................................................................................ 58 Application ............................................................................................................ 62 Stress Wave Analysis Summary ........................................................................... 63 Over-the-line Corrosivity and Corrosion Surveys ............................................................ 64 Description ............................................................................................................ 64 Application ............................................................................................................ 69 Over-the-line Corrosivity and Corrosion Surveys Summary................................ 70 CHAPTER 5: MONITORING TECHNOLOGIES .......................................................................73 Acoustic Monitoring ......................................................................................................... 73 Description ............................................................................................................ 73 Application ............................................................................................................ 75 Acoustic Monitoring Summary............................................................................. 77 CHAPTER 6: METHODS OF FAILURE MARGIN ANALYSIS AND REMAINING SERVICE LIFE ESTIMATION ......................................................................................................................79 Failure Margin Analysis Using Risk Curves Technology ................................................ 79 Description ............................................................................................................ 79 Application ............................................................................................................ 82 Summary Failure Margin Analysis Using Risk Curves Technology.................... 84 Risk Ranking ..................................................................................................................... 85 Description ............................................................................................................ 85 Application ............................................................................................................ 87 Risk Ranking Summary ........................................................................................ 88


Contents | vii

CHAPTER 7: WHAT WORKS? ...................................................................................................91 How Do I Select Pipelines/Sections for Condition Assessment? ..................................... 91 How Do I Select a Technology for Condition Assessment?............................................. 92 How Frequently Should a Pipeline Be Inspected? ............................................................ 92 Is Field Verification of NDT Results Needed? If Yes, How? ......................................... 93 What Do I Do with the Results of Condition Assessment? .............................................. 93 How Do I Reduce the Risk of Failure? ............................................................................. 94 CHAPTER 8: WHAT DOESN’T WORK? ...................................................................................97 Ignoring Consequences of Rupture in Planning Asset Management................................ 97 Not having a proper asset management program .............................................................. 97 Use of Condition Assessment Technologies with Unverified Accuracy .......................... 97 Use of Technologies for Failure Margin Analysis and Determination Repair Priority with Unverified Accuracy ......................................................................................................... 98 Overkill in Rehabilitation ................................................................................................. 98 CHAPTER 9: WHAT’S NEXT? ...................................................................................................99 Pipeline Asset Management .............................................................................................. 99 Determining Pipeline Criticality ........................................................................... 99 Acceptable Risk .................................................................................................... 99 PCCP Design Improvements ............................................................................................ 99 Build Robustness in Design of PCCP ................................................................... 99 Analysis Improvements .................................................................................................. 100 Ability to Estimate Remaining Service Life without Long History of Site-specific Data ..................................................................................................................... 100 Electromagnetic Inspection and Large Uncertainties ......................................... 100 NDT Signal Interpretation .................................................................................. 100 Verification of Acoustic Monitoring Results...................................................... 100 Future Developments ...................................................................................................... 101 Condition Assessment Technologies for PCCP with Wire Breaks Caused by Hydrogen Embrittlement .................................................................................... 101 Accurate Method for Detecting Broken Wires on Excavated LCP and ECP with Shorting Strap ..................................................................................................... 101 Ability of Fiber Optic Cable to Perform Wire Break and Leak Detection Simultaneously .................................................................................................... 101 Detection of Joint Defects ................................................................................... 101 Other Condition Assessment Technologies ........................................................ 101 APPENDIX A: RESULTS OF QUESTIONNAIRE ...................................................................103 APPENDIX B: MINUTES OF THE WATERRF WORKSHOP ................................................123 REFERENCES ............................................................................................................................131 ABBREVIATIONS .....................................................................................................................139



LIST OF TABLES Table 2.1. Rehabilitation cost data based on industry survey .......................................................10 Table 3.1. Documented experience of utilities using technologies for condition assessment and monitoring ..............................................................................................................21 Table 3.2. Documented verification of condition assessment technologies by utilities ...............22 Table 3.3. Comparison of primary characteristics of technologies for condition assessment and monitoring ..............................................................................................................23 Table 3.4. Comparison of primary characteristics of technologies for failure margin analysis and remaining service life estimation ...........................................................................29 Table 3.5. Approximate costs of condition assessment, monitoring, and failure margin analysis/service life estimation based on utility experiences .................................30 Table A.1. Responding utility, consultant, and service provider ................................................103 Table A.2. Summary of current condition assessment technology .............................................104 Table A.3. Summary of number of verified results for different technologies...........................106 Table A.4. Summary of PCCP condition assessment cost data ..................................................107 Table A.5. Summary of current gaps in PCCP condition assessment technology .....................108 Table A.6. Summary of monitoring technology experience .......................................................110 Table A.7. Summary of PCCP monitoring cost data ..................................................................111 Table A.8 Summary of current gaps in PCCP monitoring technology.......................................111 Table A.9. Summary of failure margin analysis/service life estimation experience ..................112 Table A.10. Summary of failure margin analysis/service life estimation techniques ................113 Table A.11. Summary of current gaps in PCCP failure margin analysis/service life estimation .............................................................................................................116 Table A.12. Summary of the risk mitigation strategies ..............................................................117

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LIST OF FIGURES Figure 2.1. Asset manangement and pipeline condition assessment approach.............................11 Figure 4.1. Internal visual and sounding inspection of PCCP detected a longitudinal crack in the inner concrete core .................................................................................................33 Figure 4.2. Leak detected during internal visual and sounding inspection of PCCP....................33 Figure 4.3. Hole cut in the outer core of PCCP showing crack going completely through the outer core, exposing the steel cylinder to the environment ...................................40 Figure 4.4. Wire continuity measurements along the top of PCCP ..............................................41 Figure 4.5. Half-cell potential measurement being taken on PCCP .............................................41 Figure 4.6. Magnified (100X) image of coating of a PCCP showing moderate to severe alteration in microstructure resulting from leaching due to acid attack, dissolution, and bicarbonation of the paste matrix (light-colored areas) ..................................42 Figure 4.7. Tethered Sahara acoustic leak detection system ........................................................47 Figure 4.8. Free-swimming SmartBall acoustic leak detection system ........................................47 Figure 4.9. Comparison of images from infrared and standard video collected during IR survey .....................................................................................................................48 Figure 4.10. Schematic of impact echo test setup .........................................................................61 Figure 4.11. Impact echo test being performed on top of a concrete pressure pipe .....................61 Figure 4.12. SASW test method diagram .....................................................................................62 Figure 4.13. Pipe-to-soil potential measurements.........................................................................68 Figure 4.14. Laboratory soil resistivity measurements .................................................................68 Figure 4.15. Induction-type electromagnetic soil conductivity meter (EM31-MK2 ground conductivity meter) ................................................................................................69 Figure 6.1. Example risk curves for a specific ECP design subjected to a specific height of cover and bedding and backfill condition ........................................................................81 Figure 6.2. Strains in outer core at failure of cracked outer core..................................................82 Figure 6.3. Hydrostatic testing of PCCP with broken prestressing wires .....................................82

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FOREWORD The Water Research Foundation (Foundation) is a nonprofit corporation that is dedicated to the implementation of a research effort to help drinking water utilities respond to regulatory requirements and address high-priority concerns of the water sector. The research agenda is developed through a process of consultation with Foundation subscribers and other drinking water professionals. Under the umbrella of a Strategic Research Plan, the Board of Trustees and Board-appointed volunteer committees prioritize and select research projects for funding based upon current and future needs, applicability, and past work. The Foundation sponsors research projects through the Focus Area, Emerging Opportunities, and Tailored Collaboration programs, as well as various joint research efforts with organizations such as the U.S. Environmental Protection Agency and the U.S. Bureau of Reclamation. This publication is a result of one of these sponsored studies, and it is hoped that its findings will be applied in communities throughout the world. The following report serves not only as a means of communicating the results of the water industry's centralized research program but also as a tool to enlist the further support of the nonmember utilities and individuals. Projects are managed closely from their inception to the final report by the Foundation's staff and large cadre of volunteers who willingly contribute their time and expertise. The Foundation serves a planning and management function and awards contracts to other institutions such as water utilities, universities, and engineering firms. The funding for this research effort comes primarily from the Subscription Program, through which water utilities subscribe to the research program and make an annual payment proportionate to the volume of water they deliver and consultants and manufacturers subscribe based on their annual billings. The program offers a cost-effective and fair method for funding research in the public interest. A broad spectrum of water supply issues is addressed by the Foundation's research agenda: resources, treatment and operations, distribution and storage, water quality and analysis, toxicology, economics, and management. The ultimate purpose of the coordinated effort is to assist water suppliers to provide the highest possible quality of water economically and reliably. The true benefits are realized when the results are implemented at the utility level. The Foundation's trustees are pleased to offer this publication as a contribution toward that end.

Roy L. Wolfe, Ph.D. Chair, Board of Trustees Water Research Foundation

Robert C. Renner, P.E. Executive Director Water Research Foundation

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ACKNOWLEDGMENTS The authors of this report would like to thank those water utilities, service providers, and consultants who contributed to the project through responses to questionnaires and participation in the workshop. Respondents and/or participants are Aurora Water, Calleguas Municipal Water District, Central Arizona Project, Chicago Department of Water Management, City of Calgary, City of Ottawa, City of Montreal, Cleveland Division of Water, Donahue Associates, Greater Cincinnati Water Works, Greater Lawrence Sanitary District, Halifax Water, Howard County Department of Public Works, Jason Consultants, Metropolitan Water District of Southern California, NDT Corporation, North Shore Sanitary District, North Texas Municipal Water District, Pressure Pipe Inspection Company, Pure Technologies, San Diego County Water Authority, San Patricio Municipal Water District, and Tarrant Regional Water District. In addition, the authors would like to thank the WaterRF project manager Jian Zhang and the Project Advisory Committee members Gary Burkhardt of Southwest Research Institute, Jon Kennedy of Tampa Bay Water, Brandy Kelso of City of Phoenix Water Services Department, and Alex Margevicius of Cleveland Division of Water. The authors would like to thank Albert Saul and Joan Cunningham of Simpson Gumpertz & Heger Inc. (SGH) for assistance with the literature search and Elizabeth Carroll of SGH for formatting and preparing this report.

xv ©2012 Water Research Foundation. ALL RIGHTS RESERVED.


EXECUTIVE SUMMARY OBJECTIVES This Manual is intended to be a user-friendly Best Practices Manual for condition assessment, monitoring, and remaining service life/failure margin analysis of prestressed concrete cylinder pipe (PCCP). The Manual provides an overview of available technologies, summarizes best current practices for condition-assessment and prediction of remaining service life, and provides assistance to utilities in identifying the most appropriate technologies for their system. It is also intended to provide an understanding of the limits of applicability of the available technologies and trends in future developments in PCCP condition assessment and determination of failure margin and repair priority. The manual is based on literature review and the results of questionnaires distributed to, and a follow up workshop of, water utilities, service providers, and consultants. BACKGROUND PCCP lines have been used for water transmission for more than 65 years and represent the backbone of many water systems in the U.S., Mexico, Canada, and overseas. PCCP was the pipe of choice for large diameter transmission lines throughout the U.S. in the years between the mid-1960s and the end of the 1980s. By then nearly 100 million feet of pipe had been installed throughout the United States and Canada (Clift 1991). A few ruptures of PCCP in the early 1990s created a sudden apprehension about the use of the pipe. The failures of PCCP were in general catastrophic due to their large diameter and high internal pressure. A recent study sponsored by WaterRF indicates that nearly 19,000 miles or about 5 million pipe pieces had been produced in the U.S. between 1940 and 2006 (WRF Report 91214 2008). Results of electromagnetic inspection of about 175,962 pipes (nearly 700 miles or about 3.5% of all installed PCCP) in North America indicated 6,431 distressed pipes with 1 or more broken wires (Semanuik and Mergelas 2006), corresponding to 3.7% of the total number of pipes inspected. This indicates that on the average about 96.3% of inspected pipes do not have any broken wires. The prevalence of distress in any given pipeline may differ significantly from this average rate based on a number of factors including pipe design, manufacture, aggressiveness of the environment to PCCP, and frequency and magnitude of actual transient pressure events and loads experienced by the pipeline. Distressed pipes having a small number of broken wires were providing service at the time of inspection, and would likely continue to deliver service with a risk of rupture that may initially be very low and gradually increase with time, leading ultimately to rupture. In general, distressed pipes may continue to provide service at very low risk of rupture for years or decades after the onset of distress. Based on the experience of the authors, the number of distressed pipes with high risk of failure is typically about an order of magnitude less than the number of distressed pipes. For this reason, the goal of the condition assessment process is to identify those distressed pipes with unacceptably high risk of failure and repair or replace them before they rupture, thus maintaining the desired pipeline reliability.

xvii ©2012 Water Research Foundation. ALL RIGHTS RESERVED.

xviii | Best Practices Manual: Prestressed Concrete Cylinder Pipe Condition Assessment

APPROACH The method of approach included the following:  

 

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Perform a literature review of published papers on PCCP condition assessment, performance monitoring, and service life estimation/failure margin analysis. Perform an industry survey through a questionnaire sent to pipeline operators, inspection companies, and consultants on the current state of PCCP condition assessment, performance monitoring, and determination of failure margin and remaining service life. Conduct a workshop to gather and assess utility experiences, utility needs, and utilities’ perception of gaps in knowledge for future research. Evaluate the existing condition assessment technologies based on their accuracy in identifying distressed pipe, accuracy in estimating the level and location of distress, and the usefulness of results for rational determination of failure margin and estimation of time to failure. Synthesize the gathered data into a best practice guidance manual to assist water utilities in selecting the appropriate condition assessment and monitoring technologies, frequency of inspection and monitoring, and appropriate methods for maintaining a failure margin that ensures acceptable pipeline reliability. Identify further research needed to improve condition assessment techniques and service life estimates.

RESULTS/CONCLUSIONS What Works In general, what works is a program of pipeline asset management aimed to maintain the pipeline risk of failure at an acceptable level. It generally includes periodic condition assessment, failure margin analysis, identification of pipe pieces with unacceptable failure risk, and repair or replacement of such pipes. Selection of pipelines or sections of pipelines for condition assessment should be based on criticality. Criticality accounts for the pipeline likelihood of failure, consequences of failure, and system constraints. Selection of inspection frequency and condition assessment technology is different for low, medium, and high criticality pipelines. Higher criticality pipelines require more frequent inspection and the use of advanced NDT technologies for locating and predicting the level of distress. The results from inspection using the selected NDT technology must be verified through comparison to the results from another technology or field-verification unless substantial verification of the results has already been made and is available. Once distressed pipes have been detected and the extent of distress estimated, it is necessary to determine the likelihood of failure, failure risk, and repair priority of the distressed pipes. The method of failure margin analysis used to evaluate the likelihood of failure must be based on a calibrated and verified model and must account for the uncertainties in the results of NDT technologies used for condition assessment. Risk of failure of the pipeline can be reduced in a number of ways, including rehabilitation of individual pipes or pipeline sections with


Executive Summary | xix

unacceptably high risk of failure, reduction of maximum internal pressure, or cathodic protection of an electrically continuous pipeline. What Doesn’t Work In general, what doesn’t work are not having a proper asset management program or having a program that does not properly account for system constraints and consequences of failure, does not accurately quantify the likelihood of failure, and/or does not prioritize rehabilitation based on failure risk. The consequences of rupture may include quantifiable cost due to property damage, repair, investigation, water loss, and service interruption and non-quantifiable costs, such as risk of loss of life, loss of public trust, and political fallout that should be accounted for. Ignoring or inadequately accounting for these consequences of rupture results in improper assignment of risk and misallocation of resources. Use of technologies with unverified accuracy in detecting distressed pipes and in quantifying the level of distress in such pipe can result in data that cannot be used to establish the failure margin of the distressed pipe. Inaccuracy in detection of distressed pipe can be either costly as good pipes are repaired unnecessarily or ineffective as bad pipes go undetected. Similarly, use of technologies with unverified accuracy for determination of failure margin and repair priority can lead to error in determining how close the pipe is to rupture, resulting in either unnecessary repair or failure to prioritize highly distressed pipe for repair, thus increasing the risk of pipeline failure. With limited resources, asset management by repairing all of the distressed pipe identified by an NDT inspection procedure or replacing a part of the line or an entire line with limited distress comparable to the distress level of the pipelines managed successfully by others does not work. In most cases, PCCP with limited number of wire breaks can safely perform under the design loads and pressures for many years. Replacing a section of pipeline with limited distress and a low-to-moderate risk of failure constitutes an inefficient use of scarce resources in a system that could have been managed at a fraction of cost. What’s Next The technologies needed by the utilities for improved condition assessment and pipeline asset management can be categorized into (1) pipeline asset management, (2) design improvements, (3) analysis improvements, and (4) future developments. The research needed for the development of the new technologies requires collaboration and financial support of the utilities. Utilities should pool their resources to fund the needed research to solve the challenging problems ahead. Pipeline asset management needs include methods to determine pipeline criticality using the existing data and establishment of a utility-specific acceptable level of risk. Design improvements include building robustness into PCCP design to account for future distress. Analysis improvements include the ability to estimate remaining service life without a long history of site-specific data, understanding the uncertainties of the electromagnetic inspection results near the pipe ends and for special pipes, and verification of acoustic monitoring results. Future development needs to include condition assessment technologies for PCCP that distinguish between random wire breaks caused by hydrogen embrittlement and clustered wire


xx | Best Practices Manual: Prestressed Concrete Cylinder Pipe Condition Assessment

breaks caused by corrosion, an accurate method for detecting broken wires on excavated LCP and ECP with shorting strap, ability of fiber optic cable to perform wire break and leak detection simultaneously, detection of joint defects, and other condition assessment technologies. APPLICATIONS/RECOMMENDATIONS Effective pipeline management requires allocating resources to the high risk areas of the pipeline where they are needed and not wasting scarce resources on low risk areas of the pipeline. This Manual can be used by water utilities to develop a program of condition assessment, monitoring, and rehabilitation of their PCCP lines based on pipeline criticality and failure risk. Utilities with existing pipeline management programs can use this Manual to evaluate and improve their current program. Economic Implications. Allocating scarce resources in a systematic, risk-based manner can lower the cost of pipeline management while reducing the risk of pipeline failure. The cost of properly managing a critical pipeline with distressed pipes is typically significantly less than the costs associated with pipeline failure or overly conservative rehabilitation strategies. The costs of periodic inspection and rehabilitation of pipelines with high failure risk can be spread over time to allow planning and budgeting. Management Concerns. Understanding the pipeline likelihood of failure, consequences of failure, and system constraints allows operators of pipelines to quantify their exposure and prioritize condition assessment and rehabilitation actions. Understanding the capabilities and limitations of condition assessment, monitoring, and failure margin analysis technologies allows operators to confidently select technologies that satisfy their inspection expectations and system constraints. This Manual provides a pipeline management approach that accounts for system constraints and pipelines’ likelihood of failure and consequences of failure. It also provides descriptions of technologies - including their primary applications, benefits, limitations, and access requirements. Technological Advancements. Water utilities that currently have pipeline management plans in place can use this manual to evaluate their current plan and the technologies they employ for condition assessment, monitoring, and failure margin analysis. Utilities may opt to select different technologies that are better suited for their system or have more reliable verification results. This Manual identifies areas of future technological development that utilities or other stakeholders might choose to support financially or consider using once the technologies have been developed.


CHAPTER 1: INTRODUCTION PURPOSE OF THE PROJECT AND THE MANUAL The goal of prestressed concrete cylinder pipe (PCCP) condition assessment is to identify distressed pipes and to identify and repair those pipes with unacceptable failure risk at minimum cost while keeping the pipeline reliability at an acceptable level. The overall objective of this project is to provide utilities with a best practices manual based on the available state-of-the-art condition assessment and service life estimation approaches for PCCP lines. The purpose of this manual is to provide operators of PCCP lines with an overview of available PCCP condition assessment and monitoring technologies, to summarize the best current practices for condition assessment and service life estimation, and to help operators identify the most appropriate technologies for the given constraints in their system. The manual also provides an understanding of the limits of applicability of available technologies and trends and future developments in PCCP condition assessment and determination of failure margin and repair priority. SCOPE The manual synthesizes utility experiences within North America with PCCP condition assessment technologies, monitoring technologies, and methods for determination of remaining service life/failure margin and identifies needs for future research and development based on the following:   

Literature review. More than 200 published papers were reviewed. Industry survey. A questionnaire was distributed to water utilities, service providers, and consultants (Appendix A). Workshop. A workshop was conducted with 17 participants from water utilities, consultants, and service providers to discuss and share utility experiences, needs, and practical technologies (Appendix B).

METHOD OF APPROACH OF INVESTIGATION The method of approach included the following:  



Perform a literature review of published papers on PCCP condition assessment, performance monitoring, and service life estimation/failure margin analysis. Perform an industry survey through a questionnaire sent to pipeline operators, inspection companies, and consultants on the current state of PCCP condition assessment, performance monitoring, and determination of failure margin and remaining service life. Conduct a workshop to gather and assess utility experiences; utility needs; technologies successfully employed for assessment, monitoring, determination of failure margin and remaining service life of PCCP; and utilities’ perception of gaps in knowledge for future research.

1 ©2012 Water Research Foundation. ALL RIGHTS RESERVED.

2 | Best Practices Manual: Prestressed Concrete Cylinder Pipe Condition Assessment

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Evaluate the existing condition assessment technologies for different types of pipes (e.g., LCP, ECP, ECP without shorting straps, non-cylinder pipe, etc.) based on the accuracy in identifying distressed pipe, especially identifying highly distressed pipe, prevalence of false negatives (calling bad pipe good) or false positives (calling good pipe bad). o False positive, although conservative, increases cost of repair unnecessarily and erodes owner confidence and false negative negates the purpose of assessment. o Accuracy in estimation of the level and location of distress, e.g., extent of corrosion, number of wire breaks, corrosion state of steel cylinder. o Usefulness of results for rational determination of failure margin and estimation of time to failure considering the uncertainties in inspection results and pipeline operation, e.g., determine the existing number of wire breaks and the rate of wire breakage. Synthesize the gathered data into a best practice guidance manual, referred to as “the manual,” to assist water utilities in selecting the appropriate condition assessment and monitoring technologies, frequency of inspection and monitoring, and appropriate methods for maintaining a failure margin that ensures acceptable pipeline reliability. Identify further research needed to improve condition assessment techniques and service life estimates.

BACKGROUND DATA PCCP lines have been used for water transmission for more than 65 years and represent the backbone of many water systems in the U.S., Mexico, Canada, and overseas. PCCP was the pipe of choice for large diameter transmission lines throughout the U.S. in the years between the mid-1960s and to the end of the 1980s. By then, nearly 100 million feet of pipe had been installed throughout the United States and Canada, with approximately one-half manufactured by Interpace (Clift 1991). A few ruptures of PCCP in the early 1990s created a sudden apprehension about the use of the pipe. The failures of PCCP were in general catastrophic due to large diameter and high internal pressure in the pipe. Internal and external inspection of the failed pipelines showed that other pipes in the line had internal cracks, sounded hollow when tapped, and when excavated, were found to be in a distressed state close to rupture. Water utilities with PCCP pipelines became concerned about the risk of rupture of their PCCP pipelines and some started on a program of condition assessment of their PCCP lines. Forensic investigations performed to determine the cause(s) of rupture found that some wires at the rupture site were corroded, some exhibited ductile fracture, and some exhibited brittle fracture with characteristic sharp and jagged surface. In addition, the wires on many pipes showed longitudinal splits, characteristic of dynamic strain aging resulting from the drawing process of extremely high strength wires. It was found that wires with higher tensile strength are more susceptible to brittle fracture. Brittle fracture was observed primarily on pipes manufactured during the 1970s by Interpace using extremely high strength Class IV wires, and to a lesser extent on the high strength Class III wires. PCCP was first manufactured as a lined cylinder pipe (LCP) and installed in 1942. AWWA approved a “Tentative Standard Specifications for Reinforced Concrete Water Pipe – Steel Cylinder Type, Prestressed” in 1949 (also referred to as AWWA C301-49) covering


Chapter 1: Introduction | 3

materials and fabrication of 16 inches to 48 inches diameter pipe. The first AWWA C301 standard appeared in 1952 and increased the maximum diameter of LCP to 54 inches. Embedded cylinder pipe (ECP) was developed after LCP and was first installed in 1953. In 1955, a Tentative Standard AWWA C301-55T introduced ECP with up to 72 inches diameter. Maximum standard pipe diameter was increased to 96 inches in AWWA C301-64. It included an empirical design procedure based on hydrostatic pressure tests and three edge bearing tests of each pipe design with cubic parabola interaction curve between the two (Appendix A, used primarily in eastern states) and a stress analysis design method (Appendix A, used primarily in western states). AWWA C301-72 increased the maximum standard diameter of ECP to 144 inches and included numerous changes in material specification and fabrication. AWWA C30179 (1979) increased the maximum standard diameter of LCP to 60 inches. AWWA C301-64 (1964) through -79 allowed the use of prestressing wires (referred to hereafter as “wires”) with higher strength than Class III wires. AWWA C301-84 (1984) introduced changes in material and fabrication specifications and eliminated a provision that allowed higher tensile strength of wires. In 1992, AWWA C301 was revised to incorporate new and more detailed testing of virtually every aspect of the pipe manufacturing process, including controls on wire and on mortar coating. AWWA also introduced Standard C304-92 (1992) for design of PCCP, which replaced Method A and Method B design procedures. Since 1992, changes in AWWA C301 or AWWA C304 have been less significant. The prestressing wire specified by AWWA C301 between 1949 and 1972 conformed to the requirements of ASTM A227 Standard Specifications for Hard-drawn Steel Spring Wire. ASTM A227-47 specified wire with a tensile strength in the range of 192 to 221 ksi for gage 6 and 200 to 230 ksi for gage 8 wire. In 1964, higher strength Class II wire was introduced with a tensile strength in the range of 222 to 251 ksi for gage 6 and 231 to 261 ksi for gage 8 wire. In 1972, ASTM A648 Standard Specification for Steel Wire, Hard Drawn for Prestressing Concrete Pipe (2011) was introduced. This standard specified the minimum tensile strength for Class I, II, and III wires. The minimum tensile strength of Class III wire was specified at 252 ksi for gage 6 and 262 ksi for gage 8 wire. In 1984, A648 was revised to provide both minimum and maximum tensile strengths for Class I, II, and III wires. For example, the maximum tensile strength of Class III wire was specified at 290 ksi for gage 6 and 297 ksi for gage 8. Class IV wire, although in use, was not referenced in this standard. In 1986, a supplemental splitting test using a bolt cutter was added, and in 1990 Class I wire and gage 8 wire were deleted from the standard. In 1995, a wire relaxation test was added and the splitting test by bolt cutter was removed. In 2004, ASTM A648 cautioned that strain aging caused by elevated temperature during the drawing process that lasts for more than 5 seconds at 400° F or 20 seconds at 360° F can reduce the wire ductility and increase its susceptibility to hydrogen embrittlement. In addition, a supplementary requirement was added in which hydrogen embrittlement susceptibility of the wire can be tested in accordance with ASTM A1032 in ammonium thiocyanate solution. The more significant changes in the material and the fabrication process of PCCP over the years are summarized below: 

Wire classes have changed over the years. Class I wire was used initially, and Classes II, III, and IV were gradually introduced by the manufacturers of PCCP over the years. Use of Class IV wire ended in the early 1980s due to concerns about its susceptibility to embrittlement and premature breakage. Currently the wire standard A-648 allow the use of only Class II and Class III with additional requirements to



   

reduce brittle fracture of the wire, including a supplemental requirement for testing susceptibility to hydrogen embrittlement. Minimum wire diameter was increased from gage 8 to gage 6 in 1992 due to the additional susceptibility of gage 8 wire to corrosion. Minimum wire spacing was changed to 2.0 wire diameters for ECP and 2.75 wire diameters for LCP in 1992 to prevent delamination of the coating. Coating thickness was changed several times over the years from 5/8 inch over the wire to the current minimum value of 3/4 inch over the wire. The use of cast concrete coating, which was an option from beginning, was ended in 1984. Electric continuity in the form of shorting straps laid beneath the wires and bonding of joint rings of adjacent pipes were introduced as options in the late 1970s.

PCCP PERFORMANCE HISTORY Performance history of PCCP has been recently studied and summarized in WRF Report 91214 (2008). The results indicate that nearly 19,000 miles or about 5 million (4,979,837) pipe pieces have been produced in the U.S. between 1940 and 2006. The average failure rate based on reported pipe ruptures and leaks and other types of failure (significant structural weakness discerned by inspection and loss of service) is 1 rupture in 3,000 miles per year and 1 failure other than rupture in 50 miles per year. Results of electromagnetic inspection of about 175,962 pipes (nearly 700 miles or about 3.5% of all installed PCCP) in North America by the Pressure Pipe Inspection Company indicated 6,431 distressed pipes with 1 or more broken wires (Semanuik and Mergelas 2006), corresponding to 3.7% of the total number of pipes inspected. This indicates that on the average more than 96.3% of inspected pipes do not have any broken wire. The prevalence of distress in a pipeline may differ significantly from this average rate depending on pipe design, manufacture, aggressiveness of environment to PCCP, and frequency and magnitude of actual transient pressure events experienced by the pipeline. The distress rate is typically higher in pipelines manufactured by LockJoint during the 1970s with Class IV wire and poor coating, and lower in PCCP manufactured prior to 1970 and after 1990 (WRF Report 91214, 2008). The distressed pipes having one or more broken wires were providing service at the time of inspection, and continue to deliver service with a risk of rupture that is initially very low and gradually increases as the number of broken wires grows with time, leading ultimately to rupture when the distress level (number of broken wires) reaches a limit, depending on the pipe design, when the maximum pressure in the pipe exceeds the capacity of distressed pipe with broken wires. In general, distressed pipes may continue to provide service at very low risk of rupture for years or decades after the onset of distress, i.e., the first wire break. Based on the experience of the authors, the number of distressed pipes with high risk of failure is typically about an order of magnitude less than the number of distressed pipes. For this reason, the goal of condition assessment process is to identify those distressed pipes with unacceptably high risk of failure and repair or replace them before they rupture, and thus maintain the desired pipeline reliability.


Chapter 1: Introduction | 5

PCCP FAILURE MODES Failure of PCCP may occur circumferentially or longitudinally. The failure process in the circumferential failure mode includes initiation of corrosion and ensuing wire breaks, or wire breaks caused hydrogen embrittlement, followed by cracking and delamination of the coating, loss of prestress as corrosion and wire breaks progress, cracking of the core, exposure of embedded steel cylinder to the environment, corrosion of the steel cylinder, and eventual rupture. Initiation of distress in the circumferential failure mode may be related to design, manufacture, installation, operation, or aggressive environment. Once the corrosion inhibiting properties of high alkaline cement mortar has diminished (say by cracking and/or delamination or loss of alkalinity of coating), corrosion of wire can start. In addition to the corrosion, hydrogen embrittlement of the wires with high tensile strength can occur and lead to progressive breakage of wires. Concomitant with wire breaks is loss of prestress in the core, which can lead to cracking of the core. In ECP, cracking of the core will expose the steel cylinder to corrosive elements in the soil. In LCP, the corrosion of the steel cylinder can begin with the corrosion of the wires, and pipe rupture may or may not be preceded by leakage, depending on pipe design and pressures. Longitudinal failure occurs typically due to inadequate hydraulic thrust restraint at elbows, tees, or bulkheads; differential soil settlements; or seismic ground motion due to blasts or earthquake. Poisson’s effect of circumferential strains from internal pressure and thermal loads also can contribute to the longitudinal effects. The longitudinal failure process begins with the pipe movement resulting in opening of joints or circumferential cracking of the concrete core, exposure of the steel cylinder to corrosion, yielding and rupture of steel cylinder, and failure of the outer concrete core. The process can result in leakage or rupture and may occur with or without corrosion of the steel cylinder. CAUSES OF PCCP FAILURE The causes of PCCP failure can be divided into 5 categories of design, manufacture, installation, environment, and operation. Design deficiency Design deficiency includes improper selection of the pipe type for the exposure environment and inadequate structural design of the pipe resulting from deficiencies either in the design methodology (e.g., the requirements of the standard used – such as use of very high tensile strength wire, specification of too thin a coating over the wire, or insufficient cylinder thickness or harness length for pressure-induced thrust restraint) or in the loads (e.g., improper selection of the design working and transient pressures, design earth load, and design live load). Inadequate design may also result from improper design of corrosion protection for the exposure environment.



Manufacturing deficiency Manufacturing deficiency includes improper material used in the fabrication process, improper fabrication processes such as welding, or improper labeling of the manufactured pipe, and improper quality control. Examples of improper materials include: 



Class IV wire. One of the failure modes of wire is brittle fracture of wires due to embrittlement. Very high strength Class IV wires manufactured between the early 1970s and the early 1980s and to a lesser extent some higher strength Class III wires have exhibited sensitivity to embrittlement. Sensitivity to embrittlement depends on strain aging as described earlier in this chapter (Benedict and Lewis 1999). Porous or thin mortar coating. Wire must be protected from the potentially aggressive environment by dense and durable cement mortar coating (hereafter referred to as “coating”). The increased permeability of a porous coating results in a higher rate of migration of corrosive chloride ions from the environment to the steel wire.

Other manufacturing anomalies that have occurred rarely in the past include absence of adequate tension in the wire; use of dented steel cylinder; very close spacing of wire wraps near the joint rings, resulting in coating delamination; incorrect labeling of pipe class; and deficient welds at seams in the steel cylinder or between the steel cylinder and joint ring. Installation deficiency Installation deficiencies that have caused failures in the past include inadequate bedding and backfill (especially in rocky terrain), installation of wrong pipe (e.g., lower class pipe in a higher pressure zone), coating damage during transportation, handling and installation (e.g., scraping of coating during handling or compaction, impact damage, hard joining), or improper installation of thrust restraint (e.g., not fully seated harness clamps or deficiently welded joints). Adverse environment Adverse environment is the most common cause of PCCP distress. Pipes installed in aggressive environments may require additional protection measures. AWWA Manual M9 identifies aggressive environments as those containing highly corrosive soils (soils characterized by low resistivity and high chloride or high sulfate content), severe acidic conditions, aggressive carbon dioxide, or stray currents. Operation Improper operation of pipeline can cause high stresses in the pipe resulting in distress in the form of core and coating cracking and wire break. The most common operation causes are allowing large transient pressures to occur in the pipeline or heavy earth load or live load beyond the loads for which the pipe was designed. Another common operation cause for pipelines that are cathodically protected is improper cathodic protection that typically causes rapid rate of wire break. Third party damage in some pipelines has caused rupture of PCCP.


CHAPTER 2: RISK AND ASSET MANAGEMENT FAILURE RISK ANALYSIS The purpose of failure risk analysis is to allow effective pipeline management by allocating resources to the high-risk areas of the pipeline where they are needed and not wasting scarce resources on low risk areas of the pipeline asset. The failure risk of a pipeline is typically expressed as the product of the likelihood of failure and consequence of failure. Evaluating the likelihood of failure of a pipeline requires initial information of the pipeline condition, which can be obtained from information about its design, manufacturing, installation, and operation, as well as the existing inspection results. The criticality of a pipeline is determined from the failure risk of the pipeline with due consideration of system constraints. Based on the criticality of each pipeline in the system (or each section of the pipeline), inspection priority and the need for the use of advanced condition assessment technologies (i.e., technologies that provide information about individual distressed pipe and usually at higher cost) are determined. Asset Management Process Failure risk can be re-analyzed using the condition assessment results from the advanced technologies and decisions regarding pipeline repairs and monitoring priorities can be made. Each step in this asset management process is shown in Figure 2.1 and discussed below. Consequences of Failure The first step in the process of asset management is to assess the consequences of failure, including life safety, property damage, service interruption, public trust, and political cost. Some of these are expressible in dollar value and others are not. The result of this assessment is categorization of a pipeline or a part of a pipeline to have low, medium, or high consequence of failure. Likelihood of Failure The second step is to evaluate the likelihood of failure based on available pipe data. 1. Circumferential Direction. The likelihood of failure in the circumferential direction is determined from: a. pipe age, b. past performance issues of the pipeline in the form of leaks or ruptures, c. known factors in pipe design, manufacturing, installation (including the bedding condition), environment, and operation that may increase the likelihood of failure, d. the available results of conventional condition assessment techniques, such as internal visual inspection, external inspection, and over the line corrosivity and corrosion surveys, and



e. failure margin of the distressed pipe. Based on the above factors, the pipeline can be classified into low likelihood, medium likelihood and high likelihood of failure. This process can be formalized by assigning an index approach. 2. Longitudinal Direction. The likelihood of failure in the longitudinal direction is determined from: a. the thrust restraint design of the pipeline, b. pressure in the line, and c. soil type. Furthermore, excessive differential settlement can cause failure. Temperature and Poisson effect (shortening of the pipe length from the radial expansion of the pipe wall due to hoop stress caused by internal pressure) also contribute to longitudinal stresses, but they tend to disappear as the pipe develops circumferential cracks. The thrust restraint design of pipelines for pressures in the line follows the AWWA Manual M9, Manual of Water Supply Practices for Concrete Pressure Pipe. This manual, including the procedure for design of thrust restraint, underwent significant change in 2009. The past design procedures were successful in protecting pipelines installed in stiff soils against failure, but some pipes installed in soft, plastic soils did fail. Therefore, pipelines designed and installed in soft soils prior to 2009 have higher likelihood of failure due to longitudinal effects of high internal pressure. The new M9 Manual accounts for pipe-soil interaction and for joint restraint type (mechanically restrained joints or welded joints). Unavoidable settlement of the pipeline results in longitudinal stresses in the pipe and the joint opening that should be safely resisted by the pipeline System constraints The third step is to evaluate system constraints, including (1) system redundancy, (2) the total time the line can be out of service, (3) time required for condition assessment work inside the pipeline, (4) access availability and the time and cost of constructing the needed access for the line, and (5) dewatering time and cost. Evaluation of the access should account for assessment of the in-line valves operability and the need for their repair. Criticality The results of the above three steps is integrated to determine the criticality of the pipeline. Use of advanced condition assessment technologies If a pipeline is critical, use of advanced NDT technologies such as electromagnetic inspection, leak detection, and acoustic monitoring may be justified for locating and predicting the level of distress. This information needs to be used to reevaluate the failure risk and repair priority of the pipe with the level of distress identified by the NDT technologies.


Chapter 2: Risk and Asset Management | 9

Updated failure risk Using the results of the advanced condition assessment technologies, the failure margin or likelihood of the failure of the pipeline should be determined from the distress level data obtained for individual distressed pipe and the loads acting on the distressed pipe. Based on these data, the risk of failure and repair priority of the individual distressed pipe needs to be established and the risk of failure of the pipeline needs to be reevaluated. The method of failure margin analysis used to evaluate the likelihood of failure must be based on a calibrated and verified model and must account for the uncertainties in the results of NDT technologies used for condition assessment. Rehabilitation The rehabilitation of the pipeline can be either in the form of repair or replacement of the individual distressed pipe with high risk of failure and hence high repair priority, or in the form of replacement of one or more sections of the pipeline which shows high rate of distress and high likelihood of failure. The determination of individual pipe repair or replacement of a highly distressed section of the pipeline must be based on the economic and structural evaluation of different rehabilitation alternatives. Monitoring The monitoring of a distressed pipeline can be in the form of either periodic inspection of the line or active acoustic monitoring of the line. The results of monitoring can be used to periodically update the likelihood of failure of distressed pipes for re-evaluation of the risk of failure to decide on future rehabilitation and condition assessment. Maintaining a pipeline at an acceptable risk of failure requires either rehabilitation of pipes with unacceptable risk of failure under the existing loads or reduction of the internal working pressure, transient pressure, earth load, and live load acting on the pipeline. Rehabilitation methods for individual distressed pipe pieces include, but are not limited to, pipe replacement with a closure piece, external post-tensioning, lining with carbon fiber reinforced polymer (CFRP), and installation of a steel liner. When multiple distressed pipes in close proximity of each other are interspersed with undistressed pipe, rehabilitation of the entire pipeline section may be more economical than repair of individual distressed pipes. Rehabilitation methods for pipeline sections include, in addition to those listed for individual pipe repair, replacement of the pipeline section and slip lining using steel pipe, high-density polyethylene (HDPE) pipe, or HOBAS pipe. Other methods such as robotically applied CFRP liner and cured-in-place CFRP liner are under development. Cost data and technical benefits and limitations of rehabilitation strategies collected from our industry survey are presented below in Table 2.1.



Table 2.1. Rehabilitation cost data based on industry survey Rehabilitation Strategy Replacement of individual distressed pipe with closure piece CFRP lining of individual pipe pieces

Slip lining of a section

Pipeline section replacement

External posttensioning of individual or a short section of distressed pipe and shotcrete coating

Technical Benefit Effective for limited number of highly distressed pipes. No reduction in internal diameter. Requires limited work area; excavation is required. Minimal reduction of internal diameter. Reduction of surface roughness. Effective for repair of nearly straight sections of pipelines. Minimized welding inside the pipe. Effective for repair of pipeline sections. No reduction in internal diameter. Effective for limited number of distressed pipes. No pipeline dewatering. Re-establishes the prestress in the distressed pipe. No reduction of internal diameter. Relatively rapid installation for pipes with low soil cover.

Technical Limitation Requires excavation of the pipe. May require field welding of closure piece. Requires extensive work area. Requires monitoring of CFRP installation.

Reduction in diameter may result in loss of flow capacity. Requires extensive work area and removal of several pipes. Requires excavation of the pipe. May require field welding of closure piece. Requires extensive work area along the pipeline alignment. Requires excavation of the pipe. Typically requires pipeline depressurization.


Cost (Comparative) $$$

$$$$

$

$$$

$$$

Figure 2.1. Asset manangement and pipeline condition assessment approach





CHAPTER 3: SUMMARY OF TECHNOLOGIES This chapter provides a summary of each condition assessment, monitoring, and failure margin/remaining service life estimation technology currently in use by utilities based on literature review and industry survey. Additional detail about each technology based on literature review is available in Chapters 4, 5, and 6, and additional detail based on industry survey results is available in Appendix A. This chapter serves as a guide to concisely describe each technology, its primary use, its benefits and limitation, its usage by utilities, and its comparative cost to assist readers in focusing their attention to the topics of their choice in Chapters 4, 5, and 6. Utility usage of each technology is identified as high, medium, or low in the following sections of this Manual based on the results of the utility survey and literature search moderated by our experience to account for bias in literature for newer technologies. High usage corresponds to documented usage by 15 or more utilities or documented inspection of at least 500 miles. Similarly, medium usage corresponds to 5 up to 15 utilities or 200 to 500 miles, and low usage corresponds to fewer than 5 utilities and less than 200 miles. Documented experience of utilities using condition assessment and monitoring technologies is summarized in Table 3.1. Documented verification results for condition assessment technologies are summarized in Table 3.2. Many technologies have no published verification results. Some technologies, such as impact echo and Sahara leak detection, have only limited results that may be biased because of their size. Pipe rupture is typically preceded by gradual deterioration manifested by corrosion, wire breakage from corrosion or embrittlement, loss of prestress and the resulting core cracking, separation of the concrete core from steel cylinder, and corrosion and perforation of the steel cylinder and possibly leakage (particularly in the case of LCP). Condition assessment and monitoring technologies are aimed at identifying manifestations of the deterioration in distressed pipes. Failure margin analysis of distressed pipes is used to estimate pipe margin to failure and repair priorities from the results of the condition assessment technologies used. Uncertainties in wire break data and in maximum pressure (working plus transient pressure) are included in failure margin analysis. The uncertainties may be reduced by verification of the results of condition assessment and monitoring technologies through external inspection of the identified distressed pipe and/or by performing transient analysis for improved maximum pressure estimation. Leakage in pipelines may occur at the joints or in the pipe barrel, away from the joints. Joint leakage may be a result of improper gasket installation, gasket deterioration, improper installation (especially improper bedding that causes pipe settlement), failure of joint harness (mechanical or welded), soil settlement, seismic motion, surge events, etc. Leakage in the pipe barrel occurs due to loss of water tightness of the steel cylinder due to corrosion or due to rupture caused by differential settlement or inadequate thrust restraint design near elbows, tees, or bulkheads. Corrosion of LCP, with steel cylinder and wires having the same exposure to the permeating chloride ions through the coating, is typically manifested in the form of leakage from the pipe wall before rupture (Erbay et al. 2007), especially if the internal pressure is not very high. This early warning system allows detection of distressed LCP by leak surveys; however, in PCCP under high pressure, rupture of distressed pipe typically occurs soon after the onset of leakage.



CONDITION ASSESSMENT TECHNOLOGIES Condition assessment technologies have evolved rapidly in the past 15 years. Conventional condition assessment technologies prevalent until the late 1990s were internal inspection for cracks and hollow sounding inner concrete core and corrosivity or corrosion surveys followed by excavation and exposure of the suspect pipe to verify pipe distress. Recent nondestructive inspection technologies, such as electromagnetic inspection and acoustic monitoring methods, detect and locate wire breaks in the pipe. Signal distortions in electromagnetic inspection can be used to estimate the extent of wire break. Technologies for leak detection have also evolved from detection of the acoustic signal generated by a leak from microphones attached to the pipeline at a manhole to in-line acoustic detection probes that can accurately detect and locate small leakages. See Chapter 4 for detailed descriptions of condition assessment technologies. Internal Visual Inspection (Usage: High) The purpose of internal visual inspection is to identify and document visible cracks (location, geometry, length and width) on the inside surface of the pipe, joint openings, and hollow-sounding areas (location and geometry) found when the surface of the pipe is sounded with a light hammer (generally 1 to 2 pounds) or similar instrument. Simultaneous occurrence of longitudinal cracks and hollow sounding of the inner concrete core is an indication of an advanced state of distress and significant loss of prestress in the pipe; however, individually, they may not be related to pipe distress as hollow sound in the inner core can occur near the joint rings, in low prestress ECP, ECP subjected to differential shrinkage, or ECP with dented steel cylinder and longitudinal cracking can be caused by transient events or shrinkage. Other types of anomalies, such as circumferential cracking and joint openings, observed during internal inspection may or may not be indicative of distress in PCCP. Circumferential cracks and /or joint openings may be nonstructural and caused by temperature and shrinkage of concrete, or they may be structural and caused by inadequate thrust restraint design near bends or by differential settlement near rigid concrete encasements or changes in foundation stiffness. AWWA C301-07 (2007) considers circumferential or helical cracks in the inner concrete core less than 0.060 inches in width as acceptable. Circumferential cracks exceeding 0.060 inches in width, multiple closely spaced circumferential cracks located near bends or areas of potential settlement, or cracks showing signs of corrosion require special investigation. External Inspection of Pipe Surface External Visual and Sounding (Usage: Medium) Failure of PCCP in a corrosive environment generally begins with loss of prestress due to wire corrosion (or wire and steel cylinder corrosion) and wire breakage. Due to the expansive nature of the corrosion process, delamination and cracking of the coating often occur in corrosion areas. Visual inspection and sounding of the coating can identify these areas for further investigation. Mode of wire breakage (corrosion or embrittlement) is determined by


Chapter 3: Summary of Technologies | 15

visual inspection of wires after removal of coating and opening a window in the coating for inspection of wires. Wire Continuity (Usage: Medium) Continuity of the wire for non-shorting strap ECP can be determined by measuring resistance between adjacent wire wraps. A broken wire results in a high measured resistance between adjacent wire wraps. Wire continuity measurements require excavation of a 2-foot width on the top of the pipe and localized removal of the coating at the crown of the pipe to expose the wires in a strip along the full length of the pipe and approximately 2 inches wide circumferentially. Measurement of electrical resistance between the exposed portions of adjacent wraps can identify wire breaks at any location around the pipe circumference. Wire continuity testing requires a digital multimeter with test leads, equipment to remove a strip of coating along the top of the pipe to locally expose the wires, and equipment to clean the prestressing to obtain a bright, clean metal surface for electrical connection between the wire and the multimeter test lead. Care must be taken to minimize damage to the wires during removal of the coating strip. Wire continuity measurements cannot be performed on ECP with shorting straps or LCP due to the electrical continuity of the wires provided by the shorting strap or the steel cylinder, respectively. Linear Polarization and Galvanostatic Pulse Measurement (Usage: Low) Linear polarization and galvanostatic pulse measurement are technologies for determining active corrosion in a pipe by estimating corrosion rate based on the relationship between electrochemical potential, current flow, and time. They were developed for determining the corrosion rate of reinforcement in concrete and for overcoming difficulties in interpretation of half-cell potential data. Half-Cell Potential Measurements (Usage: Medium) Half-cell potential measurements can be used to detect the existence of corrosion underneath the coating or areas with higher propensity for corrosion by measuring the difference between potential of the coating surface and the steel. The magnitude of the potential and the potential contours can be used to locate areas with higher likelihood of corrosion at the time of measurement for removal of coating and visual inspection of the conditions of wires. Potential measurement locations are generally located on a grid of points spaced 1 foot to 2 feet apart. Interpretation of half-cell potential measurements must consider temperature, moisture, delaminations, surface coatings, and other conditions that may be present and that may influence the resulting potential measurements. The half-cell potential measurement system, as defined by ASTM C876 (2009), consists of a reference electrode, an electrical junction device, an electrical contact solution, a volt meter, and electrical lead wires. Petrography and Coating Testing(Usage: Medium) The prestressing wire is protected from the corrosive environment by the high alkalinity of the cement coating applied over the wire. Wire corrosion can occur if the quality of the



coating is compromised. Quality of the mortar can be determined using concrete petrography, absorption testing, and chloride profile testing through the thickness of the coating. Poor quality of coating is a likely cause of wire corrosion and pipe deterioration. Leak Detection Walking the Line (Usage: High) Leaks in a pipeline typically find their paths to the ground surface; however, the exact location of leakage in the pipeline may not be at the point where it surfaces. Leakage of pipeline under pressure typically generates a sound related to the turbulence at the orifice that is detectable by trained ears when sources of other noise are absent. Walking the pipeline alignment during the day for visual signs of leakage or during the night for leakage noise has proven useful. Ground Microphones (Usage: Medium) Ground microphones are acoustic leak detection sensors that locate leaks from the ground surface by detecting the distinct acoustic signal generated by the pressurized water leaking from the pipe. Ground microphone systems include the ground microphone, a sensor, and headphones. Correlator Systems (Usage: Low) A correlator system has multiple acoustic leak detection sensors that identify leaks by detecting the acoustic signal generated by pressurized water leaking from the pipe, and locate the leak by comparing the arrival time of the acoustic signal to the different sensors. The sensors are placed on the pipe wall or inserted into the stream at different locations. The acoustic signals received by each sensor are then correlated. Correlator systems include at least two sensors, two transmitters, a receiver, and a data acquisition system. In-Line Acoustic Probes (Usage: Medium) In-line acoustic leak detection probes move through the pipeline and locate the sound generated by a leak. The intensity of the sound generated is related to leak size. These systems have very high detection accuracy. The acoustic leak detection probes are either tethered or freeswimming. Systems used for acoustic leak detection in large diameter pipelines include a tethered microphone with a radar system to locate the signal, and a microphone with GPS system placed inside a free-swimming ball. The location of the probe in the pipeline is monitored using receiver units on the ground surface. Leak locations are determined on the ground surface either by stopping the tethered probe at the leak location and marking the location on the ground surface or by correlating the acoustic and location data of untethered probes.



Infrared Thermography (Usage: Low) Infrared thermography (IR) can be used to detect pipeline leaks based on changes in temperature and emissive properties of the soil. Fluid leaking from a pipeline changes the temperature of the soil (Maser and Zarghamee 1997). IR survey systems require an infrared camera, a standard camcorder, and a means to survey the pipeline from a high elevation, e.g., a helicopter. Ground-Penetrating Radar (Usage: Low) Ground-penetrating radar (GPR) can be used to determine soil properties and the depth of buried objects based on the transmission and reflection properties of electromagnetic waves induced in the soil. The speed and amplitude of the transmitted and reflected electromagnetic waves are dependent on the dielectric constant and the conductivity of the soil and any objects within the soil. Increase in the soil moisture content causes an increase in the conductivity and the dielectric constant of the soil, resulting in decreased attenuation and velocity of the transmitted and reflected wave. The time delay and amplitude of the received signal appears as a distortion of the pipe compared to locations with dry soil (Maser and Zarghamee 1997). GPR survey systems require a radar, one or more antennas, and a data acquisition system. Advanced NDT Technologies for Condition Assessment Electromagnetic Inspection (Usage: High) Electromagnetic (EM) inspection is a nondestructive technology that can detect broken wires in PCCP and their locations, and estimate the number of broken wires. The location of broken wires along the pipe length and the number of broken wires at each location are predicted by analysis of distortions in the EM signal collected during inspection. EM inspection tools have been developed for pipes ranging in diameter from 16 inches to 252 inches for:   

manned and unmanned internal inspection of dewatered pipelines, unmanned internal inspection of in-service pipelines, and external inspection of in-service pipelines.

The system consists of an exciter, a detector, a data acquisition system, a power supply (batteries), and an odometer – all mounted on a customized tool that travels inside or outside the pipeline. Results of EM inspection can be used directly to assess the condition of a pipeline at the time of inspection and to obtain a measure of its remaining service life when used jointly with failure margin analysis to determine how close a distressed pipe with a number of broken wires and a maximum internal pressure is to failure. Prediction of distress level has been subject to uncertainties involved in the interpretation of signal distortions. The uncertainties are exceptionally higher for ECP without shorting strap. Unlike the pipes with shorting straps that show a linear relationship between the actual number of broken wires and the distortion of the signal, the pipes without shorting straps show a large distortion for a single broken wire and a lower resolution as the number of broken wires



increases. Another source of uncertainty is steel cylinder thickness. Electromagnetic waves are affected by the steel cylinder thickness, which typically varies along the length of the pipeline and near bends, tees, and bulkheads. Thicker steel cylinders may completely obscure signal distortions. Absence of accurate design information and pipe location can adversely influence the results of EM inspection. Additional uncertainties have been related to electromagnetic properties of the steel cylinder and the method of anchoring the prestressing wire to the concrete core and steel cylinder. The presence of shorting strap and the pipe design properties must be known prior to conducting the electromagnetic inspection. The appropriateness of EM inspection for PCCP without shorting strap should be evaluated after review of calibration results that show the actual number of broken wires and the corresponding measure of signal distortion. External EM inspection improves the resolution as it allows the use of higher frequency waves because the signal does not need to pass through the steel cylinder. High frequency waves provide improved estimation of the number of wire breaks near the pipe joints and away from the joints. Stress Wave Analysis (Usage: Low to Medium) Stress wave analysis is a group of nondestructive inspection techniques that use a controlled impact to the pipe surface to generate stress waves within the pipe wall that are detected by one or more sensors on the pipe surface spaced a known distance away from the impact location. Properties of the pipe wall and locations of defects can be determined based on the stress wave velocity and the dominant frequencies of the response. Two general types of stress wave analysis currently in use in different forms are impact echo (IE) and spectral analysis of surface waves (SASW). IE is used to identify delamination at the interface of the concrete core with either the steel cylinder or the coating. SASW is based on the premise that microcracking and cracking of concrete reduce its modulus; SASW is used to determine wave velocities in concrete, from which the modulus of concrete is determined. Over-the-line Corrosivity and Corrosion Surveys Pipe-to-Soil Potential (Usage: Medium to high) Pipe-to-soil potential measurement is an over-the-line survey used to detect areas of active corrosion by measuring the difference in potential between the soil and an electrically continuous pipeline. Potential is measured using a voltmeter with one lead connected to the pipeline and the second lead connected to an electrode that is placed on the soil over the pipeline at regular intervals. The corrosion in the pipeline occurs where current leaves the pipeline; such areas have a more negative potential than the surrounding area; therefore, areas with significantly more negative potentials relative to the surrounding areas are likely sites of active corrosion. The system for pipe-to-soil potential measurement consists of a fixed lead that is electrically connected to the pipeline, a movable lead connected to an electrode that is placed on the surface of the soil at regular intervals along the pipeline, a high impedance voltage meter, and a reliable way to measure distances along the pipeline.



Cell-to-Cell Potential Measurements (Usage: Low) Cell-to-cell potential measurement is an over-the-line survey used to detect corrosion in a pipeline that is not electrically continuous by measuring the difference in potential between locations on the surface of the soil. Potentials are measured at fixed intervals directly above the centerline of the pipeline (with reference to a stationary electrode) and at fixed distance from the pipeline centerline to determine if current flows toward or away from the pipeline. Higher negative potential at the centerline of the pipeline compared to points away from the center of pipeline is an indication of likely local corrosion. The system for cell-to-cell potential measurements consists of one stationary reference electrode, two moving electrodes, a high impedance voltage meter, and a reliable way to measure distances along the pipeline. Soil Resistivity Survey (Usage: High) Over-the-line surveys of soil resistivity can be used to identify areas where the environment may be corrosive to PCCP. Measurement of soil resistivity can be used as an initial indicator of the presence of potentially aggressive ions. Soil resistivity measurements can be made either in the laboratory using samples collected in the field or in the field using either electrodes in contact with the ground surface (Wenner four-point testing) or induction-type electromagnetic conductivity meters, which do not require direct contact with the soil. Chemical Analysis of Soil and Groundwater (Usage: High) Over-the-line surveys using chemical analyses of soil and groundwater are used to determine corrosivity of the environment to PCCP. AWWA M9 identifies environments with high chloride or sulfate content, acid conditions or dissolved carbon dioxide in the groundwater (produced from rainwater or humic acid from vegetation decay) aggressive to PCCP. Chemical analyses of soil and groundwater are generally performed in localized areas identified as containing active corrosion or as being potentially aggressive to PCCP based on over-the-line surveys. Soil and/or groundwater samples taken near the pipeline are analyzed in the laboratory to further quantify the aggressiveness of the environment toward PCCP and try to identify the cause. Protective measures or supplemental corrosion protections are generally recommended for pipes located in soils containing resistivity below 1,500 ohm-cm and more than 400 ppm water soluble chloride at the same location, soils containing over 2,000 ppm sulfates, or soils with a pH below 5. MONITORING TECHNOLOGIES Monitoring technologies in the context of this Manual are those technologies that monitor changes in the condition of the pipeline. Periodic inspection is the most common means of monitoring used, and acoustic monitoring is an advanced monitoring technology that provides direct data about the change in the condition of the pipeline. See Chapter 5 for a detailed description of acoustic monitoring.



Periodic Inspection (Usage: High) Periodic inspection using the same technologies employed for condition assessment is the most common approach for determining changes in the condition of the pipeline. For pipeline of low criticality, periodic inspection should be performed every 10 or fewer years. For pipelines with medium to high criticality, periodic inspection should be performed every 3 to 5 years, depending on the condition of the pipeline and expected change in the condition of the pipeline. Advanced NDT Technologies for Monitoring Acoustic Monitoring (Usage: Medium) Acoustic monitoring (AM) of pipelines is a nondestructive monitoring technology in which wire break events are identified and localized as they occur in a pipeline through detection of the acoustic waves generated by a wire break. Several different AM systems have been developed including hydrophone stations, hydrophone arrays, piezoelectric sensors, and fiber optic cables. The system consists of either an array of sensors installed at discrete points on the pipe wall, tethered along a cable that is placed inside the pipe through a tap, or an optical cable placed inside the pipeline, a data acquisition system, signal processing equipment, an energy supply, and a communication system for transmitting the data collected. Use of AM alone for condition assessment is limited to the identification of pipes with higher acoustic activity than other parts of the line. Higher acoustic activity is expected in severely distressed pipes that are about to fail. The results of analysis of data collected by the authors from several utilities and major users of PCCP over a span of a decade show that for wire breaks caused by corrosion, the rate of wire break does not change significantly with the level of distress in the pipe, except for pipes in the process of rupture (Zarghamee et al. forthcoming). The rate of wire break is significantly more in pipes subjected to stray current. Integration of AM data on the rate of wire breakage with electromagnetic inspection and failure margin analysis that relates the number of broken wires to pipe proximity to rupture can provide the proper basis for predicting the remaining life to rupture for distressed pipe and thus for the pipeline. UNCERTAINTIES IN NDT TECHNOLOGIES The determination of failure margin of a distressed pipe or its failure risk cannot be performed without consideration of the uncertainties in the condition assessment technology used. In general, the NDT results are in the form of signals that need to be interpreted to detect distressed pipe or to estimate the distress level and location. The uncertainty in detection or in estimation of distress level may have two sources: (1) the inherent resolution of the NDT technology in estimating the distress level in the pipe and (2) the uncertainty in the interpretation of signals where there is good resolution of the signal. Examples of the first source of uncertainty are: uncertainty in estimating the distress level from internal inspection results; uncertainty in detecting distress near the joints from the results of electromagnetic inspection of ECP; and uncertainty in estimating the distress level from the results of electromagnetic inspection of ECP without shorting straps. An example of the second source of uncertainty is the uncertainty in interpreting the number of broken wires away from joints from the results of



electromagnetic inspection of ECP with shorting straps or LCP. Due to the inherent resolution of the technology, there may exist situations where the signal is not sensitive to distress, such as the uncertainty in estimating distress level from the results of internal inspection with limited hollow sound and longitudinal cracks, the uncertainty in detection of distress levels near the joints by electromagnetic inspection, or the uncertainty in the estimates of distress level for ECP pipe without shorting strap by electromagnetic inspection. The first uncertainty source is inherent to the technology and requires verification, such as field excavation and external inspection of a sample of pipe to determine the level of uncertainty in the results. The second uncertainty source is random in nature and should be accounted for in failure margin analysis and determination of likelihood of failure. In this case, uncertainty should be accounted for by consideration of the error in NDT from calibration testing, the corrosion condition of the wires adjacent to broken wires, and propagation rate of distress in the pipe until the pipe is reinspected or repaired. These are all random variables with mean values and standard deviations from which the likelihood of failure in future years can be determined. Table 3.1. Documented experience of utilities using technologies for condition assessment and monitoring Technology Electromagnetic Inspection Acoustic monitoring Internal Visual and Sounding Chemical analysis of soil and groundwater In-line acoustic probes External visual and sounding Soil resistivity Pipe-to-soil potential survey (Close Interval Potential Survey – CIPS) Stress wave analysis Wire continuity Cell-to-cell potential survey Correlator systems Half-cell potential measurements Ground microphones

No. of Utilities Using the Technology 24 23 14 11 10 10 9

Total Inspection Length (miles) 1895 101 750 110 70 4 361

8 5 5 3 2 2 1

389 4 1 63 17