Prestressed Concrete Cylinder Pipe (PCCP) has been reliably used for more than sixty years, and is the backbone of many large water transmission networks throughout the world. Condition assessment results of PCCP over the past decade have consistently shown that the vast majority of this pipe is in good condition and represents a low operating risk. Traditionally, PCCP system operators have had to invest in expensive, intrusive, and complicated condition assessment programs to identify the few pipe sections with distress.
Today, an increasing number of PCCP operators are turning to the ePulse® external survey level condition assessment approach that enables quickly gathering data from a greater portion of their PCCP network. This information serves as an extension and validation of desktop studies, providing operators with the confidence to conduct intrusive internal inspections during planned shutdowns, and reducing the cost of internal inspections by limiting data capture and analysis to short sections with distress.
The ePulse® condition assessment technology has been used by utilities and water operators around the world on a variety of pipe materials, and involves placing two acoustic sensors in contact with the pipe. A sound wave is induced in the pipeline and travels along the pipeline. The acoustic sensors capture the time it takes the sound wave to travel between the sensor locations. For metallic and asbestos cement pipes, this measure is used to calculate the average minimum remaining wall thickness and assign a condition grade to the pipe. For PCCP, the wave velocity is used to calculate an average structural stiffness over a section of the pipeline. For PCCP condition assessment, inspection spacing is generally 10-15 pipe sticks, or between about 150 to 200 feet.
ePulse® condition assessment for PCCP has been validated against internal inspection technologies and destructive testing to verify the accuracy of locating pipeline sections with distress.
This condition assessment approach provides an indication of general condition of the pipeline segment, and provides a valuable screening tool to help determine which portions of PCCP may be deteriorating from reduced pipe wall stiffness and higher rates of degradation, including:
- Coating cracks and delamination
- Corrosion of prestressing wires
- Broken prestressing wires
- Longitudinal cracks in the inner core
- Corrosion of the steel cylinder
The results of ePulse® survey-level condition assessment can be used as a relative measure of pipe wall condition in multiple segments of nominally similar pipe, or as part of a pipeline screening and condition assessment program that includes pipe structure and failure risk analysis and localized external inspections conducted by Simpson Gumpertz & Heger (SGH). SGH is a recognized leader with more than 25 years of research, analysis, design and condition assessment, failure investigation, and repair of PCCP.
The failure risk of distressed pipes is determined by assessing the amount of identified distress and the maximum operating pressure in the pipeline. Pipe weight, fluid weight and earth load on the pipe are also considered in the failure risk analysis. The results are summarized in the form of failure risk curves that show the maximum pressure in the pipe versus the size of distress. Each risk curve is developed for a specific pipe design and soil- cover height.
Failure risk curves can be used to identify appropriate inspection tools based on the PCCP sensitivity to distress and likelihood of leakage before rupture.
Based on the pipe properties and the applied internal pressure, some concrete pipe types such as C 301 (PCCP) and C303 (bar wrapped) can leak for extended periods prior to rupture from corrosion and perforation of the steel cylinder.
An added and unique benefit of the ePulse® condition assessment approach is that it can simultaneously analyze captured acoustic data for the presence of leaks. This increases program value by avoiding the need to invest, plan, and execute separate leak detection inspections of PCCP mains. In the event that the pipe has a high criticality, the cost-effective EchoShore®-TX permanent monitoring platform can be quickly installed and commissioned to monitor several parameters, including leakage, static pressure, and other anomalies within the pipeline.
In collaboration with Simpson–Gumpertz & Heger (SGH), Echologics is performing acoustic testing and risk analysis on several miles of a critical 60- inch PCCP transmission main in New Jersey. Echologics will identify any leaks along the main, and evaluate the pipe wall stiffness along the main. SGH will perform a structural evaluation of each pipe diameter and class, provide a comparison of Echologics stiffness results, and make recommendations to identify locations where any additional inspections should be focused. During the second phase, pipe sections with distress will undergo further external inspection to evaluate the condition of the pipe and the aggressiveness of the environment, evaluate the results of non-destructive testing, and confirm the actual pipe design properties.