Ping-Ping, What’s That Sound? Acoustic Fiber Optic Technology Helps Identify Problematic Water Mains

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Courtesy of Pure Technologies

With the deteriorating state of many aging water mains found in cities across North America, urbanites are frequently witnessing unexpected plumes of water erupt as man-made geysers in their own metropolitan backyards.

While natural geysers are awe inspiring, urban geysers are much less so, due to their destruction to property, roads and the environment. Because an uninterrupted water flow is the lifeblood of every well-managed city, getting an early warning on the weak spots within the water network translates into smart municipal business, and can help prevent catastrophic blowouts down the road.

No company understands this reality better than Pure Technologies (Pure), developers behind Acoustic Fiber Optic (AFO) technology that monitors the structural health of PCCP transmission mains. Pure’s near real time AFO technology is now embraced by a growing number of pipeline operators across North America and Asia.

Reasons why water mains crack, leak and burst

Many utilties operate water mains made from prestressed concrete cylinder pipe (PCCP). This pipe consists of a concrete core, a thin steel cylinder, high tensile prestressing wire and a mortar coating. When the mortar cracks, water seeps in and corrodes the reinforcing wire.  As the wire breaks, it creates a weak spot, and as internal water overwhelms the core, the wire gives way and the pipe can burst, often with a geyser-like force.

Pure’s AFO technology monitors in near real time, the structural integrity of prestressed pipe by recording the “pings” or number of wire breaks in each main section.

“A snapping wire or two won’t break the camel’s back enough to sound an alarm bell,” says Adam Koebel on behalf of the Data Analysis Group at Pure. “But when our monitoring team notices a large number of pings from the wires breaking in a concentrated location, that’s when we focus attention on the acoustic anomalies to determine whether remedial action needs to take place.”

Koebel stresses that while it may take weeks, months or even years, eventually one extra straw will break the camel’s back and for a pipeline, that last additional cracking wire has the potential to turn a small leak into a large problem.

“Once a baseline condition has been established through electromagnetic inspection, the AFO system allows us to track the deterioration rate and identify at-risk pipes before these fail. It’s preventative medicine, and as a safeguard, it’s proven to work. The fiber never lies,” adds Koebel.

Pure AFO developed to replace limitations of hydrophone array technology

Prior to Pure’s deployment of its first acoustic fiber optic system in 2007, transmission mains were chiefly monitored using cumbersome hydrophone array technology.

This older sonic technology has limitations, especially since the system’s success depends on an array of submerged microphones embedded in the cable, all in functioning order, spaced from 100 to 200 feet apart. That’s the downside - the equipment failure rate is high in a permanent immersion environment, and each hydrophone array has a monitoring distance limited to less than eight kilometers (five miles) of pipeline.  

Comparatively, AFO technology is reliable at recording breaking (pinging) wire wraps, since the entire cable is acoustically sensitive from the start of the data acquisition unit to the end of the fiber. An AFO system can monitor 20 kilometers (12 miles) with a single system and 40 kilometers (24 miles) with a dual system. Moreover, Pure’s AFO system can be installed and function whether the mains are dewatered or in service.

Big boom theory helps promote AFO technology and PCCP management

To address the limitations of hydrophone array technology, Pure’s research and development team set out to develop a better way to improve the accuracy and reliability of pipeline monitoring.  The elusive research effort took seven years, and after consulting with leaders in the field of digital signal processing and acoustic sensing, Pure developed its own proprietary acoustic technology for PCCP environments.

“Based on the operating expense and limitations of hydrophone arrays, selling our new AFO solution was relatively easy,” says Peter Paulson, co-founder of Pure and one of the researchers behind the development of the innovative AFO technology.

According to Paulson, Pure proved the efficacy of their monitoring system during an early test run for pipeline clients.

“At the time, we had set up a demo pipeline operation on our grounds, and in a distant tent we gathered clients around to listen in around a computer screen. One of our test engineers then cut a single prestressed wire from the pipeline located a block away. Because we had amplified the sound print, the immediate resounding “boom” startled the attendees into recognizing that our AFO technology really does work. We built our reputation from there.”

The rest is acoustic fiber optic history. AFO technology is now regarded as the leading standard of PCCP monitoring.

Pure surpasses 1,120 km AFO monitoring milestone

Pure has surpassed 1,120 kilometers (700 miles) globally of active AFO monitoring. Currently within North America and China, Pure is monitoring 56 mains from a combined total of 17 clients. Pure’s active AFO system has recorded more than 43,600 wire breaks from its managed roster of pipelines located in North America and China alone.

For every AFO system, the pipeline data is streamed to a Pure data analyis team who analyze the acoustic information. Any and all wire breaks captured by the AFO system are reported within one business day to the client. If any problem is detected and confirmed, the client is notified and they can then proactively manage their pipeline by choosing how to intervene before serious damage occurs.

Koebel likens AFO data management to road repairs. “Better to repair a pothole than tear up the entire street to find the problem,” he says. “In essence, that’s the value we bring to the table. If clients don’t hear from us that means they’ve got good pipes.'

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