GERENCIA DIVISIONAL CENTRO ORIENTE CONVOCATORIA MULTIPLE 007
L. A.E. REYNA DEL ROCIO REYES PATIÑO RUBRICA
In the following sections, we have described the technologies needed by the utilities for improved condition assessment and pipeline asset management. We have categorized these technologies into (1) pipeline asset management, (2) PCCP 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 Determining Pipeline Criticality
Determining the criticality of a pipeline or a section of a pipeline and the need for application of advanced technologies using the existing data is an important step in condition assessment. Several index systems currently in use, such as “pipe criticality index” by GMRP,
“pipeline decay index” developed by Raz Konyalian, engineering consultant for SDCWA, or the index developed by SGH in a closed-form functional for EPRI (Buried Pipe Reference Guide, EPRI, Palo Alto, CA: 2010.1021470, to be published by EPRI in 2011), are examples of attempts to determine criticality from the existing data. The use of artificial intelligence approach using neural networks and fuzzy mathematics using fuzzy Markov processes has already been tried in limited cases. More work is needed to verify the results of the actual condition of a large number of pipelines where advanced technologies have been used with the results obtained from such procedures, and to develop a better index or procedure to determine the criticality of a specific pipeline.
Acceptable Risk
Is there an acceptable level of risk? Utilities have different risk aversions and do not believe that there is a single acceptable risk that can be defined for all utilities; rather, the acceptable risk depends on many factors that differ from utility to utility and should be defined for each utility. More work is needed in this area to help the utilities better define their risk aversion.
PCCP DESIGN IMPROVEMENTS Build Robustness in Design of PCCP
The tolerance of PCCP to distress, expressed in terms of broken wire, is quite different for different pipe with different design loads and pressures. There is a need for building tolerance for certain levels of distress in the design of PCCP so as to reduce sensitivity of rupture to distress. Currently, the design of PCCP considers the pipe to be free from distress.
ANALYSIS IMPROVEMENTS
Ability to Estimate Remaining Service Life without Long History of Site-specific Data The remaining service life of a pipe can be established from knowledge of failure margin in terms of the number of wire breaks to rupture and the rate of wire breaks expected to occur.
Data on the rate of failure for a specific pipeline can be obtained by multiple electromagnetic inspections or by AM. In absence of site-specific data, the rate of wire break for estimation of remaining service life can be obtained from sites of similar characteristics (Zarghamee et al.
2011). More work is needed on the rate of wire break through the life of PCCP.
Electromagnetic Inspection and Large Uncertainties
Electromagnetic inspection accuracy near the joint is far from adequate. Many false positive and false negative errors occur in detection of distressed pipe and in estimating the distress level due to uncertainty of the current technology near the ends. Similarly, the accuracy of the detection and estimation of distress level is subject to uncertainties for special pipes, such as pipes with outlet, pipes with thicker cylinder, and pipes with multiple wraps. There is a need for understanding by utilities and the consultants of the uncertainties of the electromagnetic inspection results near the pipe ends and for special pipes so that the uncertainty can be considered in failure risk analysis.
NDT Signal Interpretation
Understanding the capabilities, accuracy, and uncertainties of each NDT technology is a responsibility of utilities. Furthermore, understanding the intricate relationships between the signal of an NDT technology and the actual level of distress in the pipe (from which failure probability, failure margin, or time to failure can be estimated) is an essential part of successful condition assessment. This relationship needs to be made clear to the utilities and the users of technologies. Practical limitations and uncertainties in the application of NDT technologies should be identified and eliminated through research.
Verification of Acoustic Monitoring Results
There is a need to show the accuracy of AM results. For this purpose, a series of distressed pipes should be subjected to SGH wire continuity test before and after a period of time in which multiple wire breaks have been recorded and located. At each time the pipes are excavated and electric continuity test is performed to determine the actual wire breaks and their locations. Comparison of the results with AM test will reveal the accuracy in detection and location of wire breaks by AM during the monitoring period.
FUTURE DEVELOPMENTS
Condition Assessment Technologies for PCCP with Wire Breaks Caused by Hydrogen Embrittlement
Hydrogen embrittlement breaks, unlike the wire breaks caused by corrosion, do not align and occur randomly along the length and around the circumference of the pipe. This has been observed in pressure testing to failure of pipe with more than 120 broken wires where pressure at rupture was not significantly affected relative to a good pipe. This is due to the fact that random wire breaks result in residual prestress in the pipe that prevents the core from cracking. Such a technology should be able to detect accurately the number of broken wires and the stiffness of the pipe wall. For hydrogen embrittlement wire breaks, distress is not then defined solely on the number of wire breaks but on the combination of pipe wall stiffness and number of wire breaks.
There is a need to distinguish between random wire breaks caused by hydrogen embrittlement and clustered wire breaks caused by corrosion.
Accurate Method for Detecting Broken Wires on Excavated LCP and ECP with Shorting Strap
SGH has developed a simple wire continuity test of adjacent wire wraps to identify the breaks in the wire wraps for ECP without shorting strap. For this test, the top of the pipe is exposed, the coating is removed over a 2-inch-wide strip, and resistance of adjacent wire wraps is measured. This procedure is highly accurate for identifying and locating individual wire breaks, but it is not applicable to ECP with shorting strap or to LCP. There is a need to develop a similar test that shows accurately where wire breaks are located in an ECP with shorting strap or in an LCP.
Ability of Fiber Optic Cable to Perform Wire Break and Leak Detection Simultaneously Since wire break and leak detection are both acoustic, it is reasonable to expect that a technology can be developed to perform both wire break detection and localization and leak detection and localizations simultaneously. As a first step to this goal, the ability of fiber optics to resolve the acoustic event from turbulence noise in high velocity lines need to be developed and demonstrated.
Detection of Joint Defects
The joint defects in the form of poorly grouted joints expose the joint rings to corrosion.
The corrosion of joint rings may result in brittle wire breaks as hydrogen is released at the cathode. There is a need for a technology that can be used to detect joint defects in PCCP lines.
Other Condition Assessment Technologies
Average pipe wall stiffness: Areas of reduced pipe wall stiffness have been detected in cast iron pipe and asbestos cement pipe by measuring the velocity of a wave traveling through
the water in a pipeline. A controlled wave induced in the pipe travels as a compression wave in the water along the pipeline and dilates the pipe. The wave velocity decreases in areas of reduced pipe wall stiffness, and the average velocity between two points can be used to calculate the average pipe wall stiffness using established relationships between pipe stiffness and water bulk density (Bracken and Johnston 2009).
Verification of stress wave propagation inspection results: Impact echo inspection results have been verified by Sack and Olson (1994) and by Zarghamee and Maser (1997); however, the use of SASW for determining concrete core modulus and pipe stiffness and detection of distressed pipe has not been verified. There is a need for such verification. Once the technology is verified, pipe stiffness measured by SASW can be used for detection of distressed pipe.
Inductive scan imaging: Detection of defects (fractures or corrosion) in steel embedded in concrete is a developing area for application of the inductive scan imaging technique.
Experiments performed on pipelines in Libya show that the technique is able to identify broken or corroding prestressing wire from the exterior of the pipe and locate the distress in the circumferential direction.
PCCP vibration frequency: Prestress loss due to prestressing wire breakage may result in reduction of pipe stiffness and changes in the natural frequency of vibration. Work on the correlation of the natural frequency of PCCP with broken wire length has been reported (Alavinasab et al. 2010).
Detection of cylinder corrosion by electromagnetic inspection: Development is underway for electromagnetic inspection technology to detect corrosion of the steel cylinder in LCP (Pure Workshop statement).
Laser profiling: Geometric evaluation of a pipeline interior surface can be performed using laser profiling technology. A model of the pipeline interior can be reconstructed using the data collected during inspection and can be used to quantitatively evaluate the pipe interior surface for irregularities such as spalling, deterioration of inner core, and inside joint mortar loss (Kwak et al. 2007).
APPENDIX A: RESULTS OF QUESTIONNAIRE
SURVEY OF PCCP CONDITION EVALUATION PRACTICES Background and Objectives
As a part of the industry survey process, a questionnaire was sent to utilities, consultants, and service providers in order to get a broad perspective on the engineering practices on PCCP condition assessment, performance monitoring, and service-life estimation in the past 12 years.
The questionnaire was sent out to 64 water utilities, 23 consultants, and 10 service providers.
Fifteen utilities, 1 consultant, and 1 provider responded (Table A.1). These responses often were presented in sentence fragments; in that case, an attempt has been made to complete the view expressed in the comment with a minimum of editing. The survey questions fall into 4 categories: condition assessment technology, monitoring technology, failure margin analysis/service life estimation, and risk mitigation. The following synthesis of the survey responses is organized accordingly.
Table A.1.
Responding utility, consultant, and service provider
Responding Utilities Abbreviation
The City of Calgary Calgary
North Texas Municipal Water District NTMWD
Cleveland Division of Water CDW
Greater Cincinnati Water Works GCWW
San Patricio Municipal Water District SPMWD
Howard County Department of Public Works HCDPW
San Diego County Water Authority SDCWA
Metropolitan Water District of Southern California MWDSC
Aurora Water Aurora
Central Arizona Project CAP
Halifax Water Halifax
Calleguas Municipal Water District Calleguas
Tarrant Regional Water District TRWD
Greater Lawrence Sanitary District GLSD
City of Montreal, Québec, Canada Montreal
Chicago Department of Water Management Chicago Responding consultant Abbreviation
Jason Consultants Jason
Responding provider Abbreviation
NDT Corporation NDTC
Synthesis of Survey Responses
To be consistent with the arrangement of the questionnaire, all survey responses are summarized in tables and presented in four parts below:
Part I - Condition Assessment Technology Experience Overview Part II - Monitoring Technology Experience Overview
Part III – Failure Margin Analysis/Service Life Estimation Experience Overview Part IV – Risk Mitigation Overview
Part I – Condition Assessment Technology Experience Overview
Part I of the questionnaire was focused on PCCP condition assessment technologies used by the responding utility during the past 12 years. For each technology used, the utility was asked to complete a form included at the end of the questionnaire to provide more details and comments regarding the technology. These responses for 18 technologies currently in use by the responding utilities are summarized in Tables A.2 through A.4. Part I also contained an open-ended question concerning gaps in the existing condition assessment technologies. Answers to this question are presented in Table A.5.
Table A.2.
Summary of current condition assessment technology
Technology
Reliable in identifying wire breaks.
The most quantifiable method and extremely cost effective.
Most effective when used to find pipes with a lot of wire breaks.
Technology condition to be targeted.
The results had a
Identifies areas of stray currents.
Cathodic protection masks almost all the issues.
Soil Resistivity 10 362 2010
Soil Chemical Analysis
10 107 2010 Good first screening to determine areas that have a risk of failure due to soil condition.
Half-Cell Potential 4 223 2010
External Inspection 10 4 2010 A clean and easy way to
Technology used to detect leaks in LCP
Summary of number of verified results for different technologies
Technology
1 Results of only one verification test were provided for each Sahara and SmartBall leak detection systems. These technologies have been shown to be successful for leak detection based on experience of SGH and as documented by literature review.
Table A.2 (Continued)
Table A.4.
Summary of PCCP condition assessment cost data
Inspection
Internal 148 $10k TRWD Staff inspects
RFTC
0.6 to 2.5 $56k Halifax Manned and PipeDiver used for inspection. Additional $32k per mile in utility costs.
0.5, 0.17, 0.5, 1.5
$13k MWDSC Tests for side-by-side comparison with P-Wave.
2 to 9 $12 to $16k MWDSC
$15k SDCWA Total inspection length not provided.
148 $10k TRWD
10.1 $50k NTMWD Including cost of dewatering, cleaning, ventilation, inspection, testing and external inspection for verification.
13.4 $64k Calgary PipeWalker, PipeRanger, and PipeCrawler used for inspection.
Response does not specify if access costs are included.
P-Wave
4.25 $28k Aurora With internal inspection by provider.
0.5, 0.17, 0.5, 1.5
$19k MWDSC Tests for side-by-side comparison with RFTC.
1.2 $64k Calgary P-Wave and Wet P-Wave used for inspection. Response does not specify if access costs are included.
Pipe-to-Soil 148 $0.5k TRWD
Resistivity
27.8 $2k San Patricio Localized external inspection for verification. Cost of access exceeded cost of inspection.
SmartBall 10.1 $11k Calgary
Sahara 2.7 $23k Calleguas No access costs necessary.
10 $5k TRWD
External 8 pipes $10k per pipe Calgary Excavated pipe, inspected pipe coating, and hydroblasted coating to expose prestressing wires.
Notes:
1) No adjustment made for exchange rate at time of inspection 2) No adjustments for year of inspection
Table A.5.
Summary of current gaps in PCCP condition assessment technology
Subject of Response Response Author Accurate method to detect
broken wires on excavated
A good method for finding wire breaks after excavating pipe sections
based upon internal testing methods. CAP
Capability to perform condition assessment with pipeline in service
Allow economical assessment without removing large diameter
pipelines from service. SDCWA
RFTC needs to be less intrusive to the system (no shut down for access). Positive progress with PPIC PipeDiver.
Halifax
In-the-wet electromagnetic testing for very large diameter pipe CAP
Current ability to perform condition assessment while pipeline is
under pressure and/or low flow velocity is a significant limitation.1 GCWW
Non-destructive
electromagnetic inspection calibration
Calibration data used to estimate the number of wire breaks require destroying a pipeline; calibration data must be determined for both ECP and LCP for differing pressure classes (prestressing strand spacing) and diameters.
GCWW
RFTC: Degree of accuracy is dependent on “calibrating” to actual
pieces of pipe. SDCWA
Electromagnetic inspection accuracy near joints
RFTC wire break sensitivity and quantification accuracy near joints. MWDSC
RFTC does not pick up wire breaks near joints. Calleguas
RFTC technology is suspect in joint areas of the pipe. SDCWA
RFTC needs to be more accurate at bell and spigot ends. Halifax
Electromagnetic inspection accuracy on pipe with nonstandard properties
RFTC wire break sensitivity and quantification in pipes with thick cylinder, and other non- standard PCCP fabrication configurations.
MWDSC
RFTC technology is suspect in double wrap pipe. SDCWA
Large variances with external inspections results, both
underestimating and overestimating the number of wire breaks in 252-inch-diameter pipe and several false positive results in smaller diameter non-cylinder pipe.
Correlation between P-Wave technology and accurately locating
distressed pipe areas and estimating number of wire breaks. Aurora
Lack of / unacceptable correlation between RFTC and P-Wave wire break existence predictions; limited availability of P-Wave wire breaks prediction verifications.
MWDSC
Clarification of minimum RFTC WB sensitivity in non-shorting strap PCCP: 1 WB or sufficiently rusty splice reported as 5 WB, which presents potential to overestimate by a factor of 5, especially with multiple break regions.
MWDSC
Clarification of minimum RFTC WB sensitivity in shorting strap PCCP may be 5 – 20 WB depending on position; higher potential to underestimate or miss WB, especially near joints.
MWDSC
Remote Eddy Current Evaluation – Reliability of number of wire
breaks. GCWW
1 Technologies are currently available to perform electromagnetic inspection of in service pipelines. See Chapter 4 for details of the available technologies.
(continued)
Subject of Response Response Author
Distinguish multiple wire breaks in short distance from a few wire
breaks spread across the same area. Aurora
Lack of certainty in number of wire breaks with electromagnetic
inspection. CDW
RFTC: More verification of survey results is required. SDCWA Electromagnetic inspection
cost RFTC needs to be lower cost. Halifax
Failure margin analysis
Remote Eddy Current Evaluation – what does it really mean and at what point is the information able to determine whether or not a pipeline is bad or in jeopardy.
GCWW
Corrosion detection and probability with time
RFTC can’t detect wire corrosion. CDW
Inability to detect levels of corrosion on prestressing wires. Chicago
Corrosion probability versus time to initiation of or existence of corrosion; locating small, but structurally significant corroded areas on PCCP.
MWDSC
Detection of joint defects No “technology” other than visual is available to identify separated,
damaged, seeping, and leaking joints during internal inspections. MWDSC Differentiation between wire
breaks due to corrosion and embrittlement
Rapid determination of embrittlement versus corrosion damage. TRWD
Verification of stress wave propagation inspection results
Verification of test results of stress wave propagation methods. This would greatly improve data interpretation of test results and add creditability to the testing industry.
NDTC Unmanned visual inspection
of in-service pipeline
Visual internal inspection of force mains that are too small for human
entry without dewatering. Jason
Part II – Monitoring Technology Experience Overview
Part II of the questionnaire was focused on PCCP condition monitoring technologies used by the responding utility during the past 12 years. For each method used, the utility was asked to complete a form included at the end of the questionnaire to provide more detailed experience and comments regarding the technologies. These responses for the 5 monitoring technologies in use by the responding utilities are summarized in Table A.6 and Table A.7. Part II also contained an open-ended question concerning gaps in the existing condition monitoring technologies.
Answers to this question are presented in Table A.8.
Table A.6.
Summary of monitoring technology experience
Monitoring
Benefits of real time reporting.
Used in conjunction with baseline inspection information to determine break rate and threshold for repair /replacement. break rate and threshold for repair/replacement.
Cost effective for short length and short time period.
Helpful in identify the magnitude of the failing pipes.
Helpful for gathering
information on time frequency of wire break event to predict rate of deterioration in
Piezoelectric Sensors 2 2 2010
Piezoelectric Sensors 2 2 2010