Acoustic technology helps utility assess major transmission main and prioritize resources.

The city of London, Ontario, is situated at the confluence of the Thames and North Thames rivers just above Lake Erie. The city draws 25% of its water from the lake, and maintaining the transmission system is a critical task.

London is Canada’s 11th largest metropolitan area, with a population of more than 380,000 residents. The city continues to grow and develop, which has led to many transportation projects along the Elgin pipeline corridor, the large-diameter water main network that brings Lake Erie water to the city.

With the network’s significance to the city’s water supply, as well as the number of overlaying projects, taking a proactive approach toward maintenance has become increasingly important.

“We had some major projects, including a road widening and pipe life-cycle replacement,” says Taylor Eckert, city project engineer. “By getting ahead of these projects with inspection and understanding the pipe’s condition, it gave us the opportunity to piggyback on the larger transportation projects and save on replacement investment.”

New approach

At many municipal utilities like London’s, water asset managers are adopting a pyramid approach to pipe condition assessment. On a selected group of assets, the concept uses cost-effective methods to collect information where possible and progress to high-resolution and high-cost inspection options where needed. This approach formed the structure of London’s project plan for its Elgin large-diameter pipeline.

The assumption was that the pipeline was in good condition, but they needed to confirm this assumption with evidence-based information to mitigate the likelihood of failure and extend the life of these high-risk assets while at the same time meeting legislative requirements.

Following a comprehensive evaluation process, Echologics ePulse was chosen to assess the minimum average structural stiffness of approximately 9 miles of large-diameter prestressed concrete cylinder pipe mains. Echologics EchoWave leak detection was used on 6.5 miles of large-diameter steel mains. This segment, installed in the 1990s, consisted of water mains with diameters ranging from 35 to 41 inches. The goal was to conduct a due diligence inspection to determine the current pipe condition and put forth recommendations for the city to make evidence-based asset management decisions to replace, rehabilitate, defer or monitor specific lengths of this pipeline.

“As water pipes increase in diameter, they also increase in criticality and complexity. Transmission pipes are site-specific installations. Each transmission pipe has been designed to ensure safe operation, given local loading and operating considerations,” says Alain Lalonde, regional manager of Water Management Solutions at Mueller Water Products. “Decades after a transmission pipe has been installed, design standards, actual loading conditions and consequences of failure may change significantly. Hence, understanding the current structural state and operating requirements of each transmission pipe is a critical step toward making evidence-based asset management decisions.”

The ePulse technology uses a cross-correlationmethodology to combine acoustic data measured in the field with information about a pipe’s construction to calculate the average minimum remaining structural pipe wall stiffness over the measured segment. As a pipe degrades, the velocity at which sound waves travel through the pipe decreases linearly, forming the basis for the technology. The pipe assessment is performed by bracketing a section of pipe between two sensors that are attached to an existing valve or exposed pipe wall. An out-of-bracket noise is then created by tapping on a valve or directly on the pipe via a daylighting pothole.

The field team measures the distance between the two sensors. The wall stiffness is determined using the measured sound wave propagation speed through the pipe and comparing that value to the wave speed of a new concrete pipe in perfect condition. This calculation takes into account the pipe and water properties for the specific classes of concrete pipe tested. For this particular project, all pipe properties were determined from drawings provided by the city.

“When looking into areas such as ease and resolution of inspection and low operational risk, ePulse checked all the boxes,” says Michelle Morris, transportation design engineer for the city of London. “Echologics also worked with us to formulate a grading scheme to quantify the pipe’s condition and detailed next steps that should be taken for segments exhibiting each particular grading.

“Having this concrete data and grade scheme in place, we can easily add this into our database, which will help with the scope of work in the future by establishing a baseline with historical data.”

Echologics field engineers also worked with the city’s water engineers to ensure a smooth migration of inspection data into their existing GSI database, making it more accessible and easier to understand by the asset management team.

System analysis

For a more comprehensive assessment of the pipeline, Echologics, as the prime contractor, teamed up with several expert consultants to conduct in-depth high-resolution testing and review. The ePulse technology provided rating for the average remaining structural stiffness of each length of pipe tested and identified lengths of pipe where significant structural deterioration had occurred. These findings were paired with Simpson Gumpertz & Heger’s structural evaluation and failure risk analysis results to identify at-risk s ections of the pipeline.

Based on high-resolution ePulse analysis and stiffness measurements, there was sufficient data to show that close to 80% of the tested mains are in good condition and will not require further investigation, although periodic inspection and maintenance work are encouraged. The remaining 20% showed some signs of deterioration and will require attention in the future.

The added advantage of this acoustic technology is the ability to conduct leak detection simultaneously. No leaks were discovered at the time of the survey on the Elgin pipeline. The fact that no existing leaks were found on this pipeline was an early indicator that no immediate or emergency rehabilitation or repair actions were required.

After the six-week period, the city could move forward with peace of mind, knowing that this critical pipeline is in good condition. The successful inspection and assessment allowed the city to allocate its limited budget toward water mains that had a greater level of degradation and need for renewal.

Jay Shah is the Echologics major projects manager for Mueller Water Products.

Click here to read the article in Municipal Sewer & Waste