Utilities looking to assess their aging buried infrastructure have historically had two options, invasive high-resolution technologies and their associated high cost or alternatively low-resolution non-invasive solutions and their associated reduced level of actionable data.
Pipe condition assessment technology (p-CAT) provides a high level of actionable data while maintaining the low-cost structure and ease of deployment associated with non-invasive solutions to provide utilities and engineering firms with a verified assessment tool for their pressurized pipe condition assessment needs.
p-CAT is a non-invasive pipe screening tool that utilizes the pressure of the pipe to measure and calculate the remaining wall thickness, gas pockets, material changes, obstructions and sealing status of valves. Originating in Australia, p-CAT utilizes a unique patented method of assessment in which a controlled inverse pressure transient of 5 to 8 psi is introduced into the pipe via a ≥ 2-inch access point (i.e. ARV, scour valve). This pressure transient propagates down the pipeline and is recorded on high speed pressure transducers capable of covering over a mile of pipe in a single test. The measured transient illustrates the various reflections and variations in the pipe wall strength as it travels between locations.
p-CAT has been refined over 17 years of research and development in partnership with Detection Services Ltd. and the University of Adelaide in Australia. p-CAT is suitable for a wide array of pipe diameters and materials including all metallic, asbestos cement and non-reinforced concrete pipelines. While each test taken with the p-CAT tool can cover more than one mile in length, the analysis of the pressure transient waves allow for sub-sectional analysis capable of identifying changes in the wall thickness as small as 0.007-in. along sections of pipe as short as 30-ft lengths. Compared to traditional averaging tools that measure between two test points, p-CAT provides a higher level of detailed analysis to empower engineers and owners to prioritize their rehabilitation and replacement budget.
Localized fault detection analysis also allows p-CAT to identify pipeline anomalies such as gas/air pockets, material and diameter changes, blockages, sealing issues with valves and other unknown pipeline features.
City of Louisville, Colorado
Founded as a small mining town in 1878, the City of Louisville Colorado has since grown to a population of more than 21,000 residents. Expanding from its first water treatment plant built in 1934 to its current operation of three treatment plants, Louisville supplies its businesses and residents with nearly 1.3 billion gallons per year via a distribution network of more than 120 miles of pipeline.
Originally installed in 1955 to provide the City of Louisville with its raw water needs, this critical aging pipeline now supplies nearly one third of the City’s water needs. This “can” pipe was constructed of steel sheets that were rolled into cylinders then welded together and coated with a coal tar layer. Stretching nearly 8 miles from intake to reservoir and ranging in size from 14- to 18-in., this pipeline started showing its age in the 1980s as failures started to occur. Mainly caused by external corrosion, leaks started popping up along the length of the pipe. Early intervention with the installation of cathodic protection sites slowed the deterioration and in the following decades little improvements were made.
Realizing the implications if this pipeline failed, the City of Louisville, led by deputy director of utilities Cory Peterson, set out to better understand its current condition. Multiple assessment tools were studied including invasive technologies such as internal robotic camera inspection, tethered ultrasonic testing and internal leak survey. Each had their associated draw backs from cost, operational limitations and lack of pipe wall assessment. Ultimately, p-CAT was chosen as it fit within the planned budget and provided the necessary information including pipe wall thickness. According to Cory from the City of Louisville, the biggest advantages to p-CAT were “its ability to test long distances relatively quickly” and “keep the pipeline essentially live during the assessment.”
While p-CAT has been independently validated extensively overseas, the Louisville Colorado pipeline is the first validation study since the introduction of p-CAT technology to the U.S. market in 2017. To perform this validation study, Dewberry Engineers Inc., a firm familiar with verification studies, was contracted to independently establish the validity of the p-CAT inspection results. In order to perform this validation study, the City removed a 40-ft section of pipe that had previously been identified for replacement as part of a separate improvement project.
To evaluate the p-CAT assessment results, a higher resolution tool was utilized to provide accurate measurements. Consequently, Eddy Current technology was determined to be the best method given the pipeline variables and potential for asbestos within the coal tar lining. Dewberry selected JanX INCOTEST to provide the high-resolution Eddy Current Assessment. Sensors were spaced every 2.5 in. around the full circumference of the pipe. Capturing a reading every 0.941 in. along the entire length of the 40-ft section, nearly 10,000 data points were collected. The resulting data measured the pipe wall thickness along the assessed section to be 0.171 in. For the same stretch of pipe, p-CAT identified the wall thickness to be 0.17 in.
“The wall thickness that Hydromax USA’s p-CAT reported was spot on with the eddy current wall thickness results,” said Carl Bundschuh, P.E., senior associate at Dewberry Engineering.
Having verified data along at least one stretch of the assessed pipe has been extremely beneficial to the City of Louisville, Colorado. Peterson stated, “Prior to the assessment, the biggest challenge was not understanding what condition the pipe was in. With this project we were able to get a sense of the pipe’s condition and push off the larger capital project that included the possibility of replacing whole sections of this pipeline.”
p-CAT provided a high level of actionable data without the associated high price tag. Verification of the Louisville pipeline results exemplifies this.
The INCOTEST/Eddy Current Test and the Hydromax USA p-CAT analysis all found the average thickness of the removed pipe to be approximately 0.17 in.
Carl Bundschuh, P.E., had the following comment on p-CAT’s results, “I was surprised the results were as accurate as they were, further validation would be great in a second location but overall p-CAT is a really nice assessment tool that can be used everywhere without having to excavate and expose large sections of the pipe. It’s a relatively inexpensive assessment tool and assesses long reaches of pipeline rapidly.”