PWA: A Strong Choice for Screening Assessment of Metallic Pipelines


Source: Pure Technologies - a Xylem brand

As pipelines across North America age and begin to reach their end-of-life cycles, utilities are faced with the task of assessing their network and determining the best course of action for maintaining reliable, efficient and sustainable levels of service. The task of selecting pipes for inspection, rehabilitation or replacement can be overwhelming.

For the majority of metallic pipelines, it is valuable for utilities to complete a low resolution screening assessment that combines inline leak detection with pipe wall assessment (PWA). PWA is a new technology that can identify areas of increased stress on a pipe-by-pipe basis. Stress on the pipeline can be indicative of significant pipe wall deterioration, cracking or other areas of concern such as bending or overloading. On lower risk mains, PWA can be paired with traditional techniques to more knowledgably select test pit locations and successfully manage the pipeline. On medium and high risk mains, the low resolution assessment is used for screening and prioritization prior to employing higher resolution technologies. 

Pipe Wall Assessment Platforms

For utilities undertaking a low resolution inspection, Pure Technologies’ SmartBall® and Sahara® PWA tools combine leak detection and PWA in a single deployment to provide a comprehensive low resolution solution. This is important because in many cases, metallic pipe failures are preceded by a period of leakage. By combining leak detection and PWA, utilities can identify both leaks that could lead to eventual failure, and areas of stress that could represent wall loss or damage.

The PWA technology reads changes in the magnetic field of the pipeline which fluctuates when the metallic pipe is under stress. The presence of stress can be indicative of physical defects like corrosion and cracks or external conditions such as excessive overburden or point loading. Additionally, other pipeline features can be identified such as joints, some appurtenances and changes in material. Identification of joints is significant in that data is collected as the tools pass through the pipe, then analyzed and reported on a pipe-by-pipe basis.

Utilities Using Pipe Wall Assessment for Low Resolution Assesment

When the City of Tarpon Springs – a small utility with limited resources – wanted to perform a 1-mile condition assessment on its 14-inch ductile iron Dixie Highway Force Main, they chose the SmartBall PWA tool as the best option to accurately assess the main. The SmartBall, deployed into the force main through a check valve at the pump station, travelled downstream and collected data as it rolled through the pipeline with the flow. The data was analysed and the survey identified no leaks and nine gas pockets, as well as six pipe sections with increased stress, five that could not be traced to force loading. Based on the inspection, it was recommended that air release valves be installed along the force main to clear gas pockets, which can be of significant concern in force mains. The inspection also allowed the City to make more informed decisions about the next steps in their inline assessment program.

The Sahara PWA is a tethered tool that is inserted into a pipeline through a 4-inch tap or larger while the pipe is still in operation. The sensors which collect data are pulled through the pipeline using a parachute attached to a data acquisition unit above ground, providing real-time identification and location of leaks and gas pockets. The additional benefit of the Sahara PWA tool is the high-resolution video camera that provides real-time visual information on the internal condition of the pipe. PWA data is collected during the inspection for analysis.

Sahara PWA was used for an inspection with the Louisville Water Company, who proactively undertook an assessment program after three major failures on one of its oldest and most critical 48-inch cast iron water main. Louisville Water and Pure inspected 4.6 miles of the main, identifying 7 leaks, as well as many pipes with stress anomalies. By proactively assessing the condition of its most critical mains, Louisville Water is able to repair leaks, visually confirm the internal condition of the main and direct test pits to better understand the condition of the pipeline.

Pure Technologies’ PWA tools can effectively screen pipelines, giving utilities the information they need to develop proactive management plans for their assets.

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