Maple Ridge, B.C., a district in northeast Vancouver, experienced up to 20 breaks per year in older water pipes, mostly in the middle of the night when pressures were highest. Water surfaced or sometimes washed out small sections of road.
The Waterworks Department repaired breaks as they occurred, plotting their histories on maps and looking for clusters that warranted further investigation.
“This is a growing community with a fairly young infrastructure,” says superintendent Ed Mitchell. “Except for 42 miles of asbestos cement and cast iron pipes with some ductile iron, we’re in good condition. Our main driver in investigation and replacement was trying to determine a pipe’s remaining useful life.”
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Occasionally, the district sent sections of pipe to a laboratory for destructive analysis — expensive but more affordable than replacing lines prematurely. Mitchell looked for a more economical, non-destructive way to assess the system and set priorities for pipe replacement.
He found Echologics, a developer of advanced acoustic-based technologies for leak detection and pipe condition assessment. In 2007, the district hired the company to survey 21 locations on 3.5 miles of pipe spread throughout the system. Technicians returned the following year to survey 30 locations across five miles of the system.
The district distributes a billion gallons of water per year to 69,000 residents. It has 240 miles of pipes, 18,000 service connections, seven pump stations, and six reservoirs. Pipes prone to breaking comprise 18 percent of the system, with velocities below 3 feet per second and pressures around 80 psi.
For each survey, Mitchell chose lines with some failures. “Even if it was one or two breaks, we wanted the assessment information added to the history we had on that line,” he says. “We were happy with the results. Last year, we reprioritized our replacement list, hiring Echologics to assess 13 locations on 1.25 miles of pipe.”
The length of each analysis depended on access to the line. Working 300 and 650 feet between valves produced the best results. Technicians substituted fire hydrant valves if inline valves were unavailable. The longest runs were close to 1,300 feet.
“We provided a spreadsheet for the technicians with the length, diameter, material, and pipe class, and ensured that they had easy access to the valves,” says Mitchell. “They usually wheeled off the section to be analyzed to get a more accurate measurement of pipe length. We also sent a water operator to help with traffic control when the valves were in intersections. That’s all we did to prepare for an evaluation.”
Riding the wave
The basic LeakFinderRT system includes two high-frequency sensors, two wireless transmitters, a two-channel wireless receiver, headphones, battery charger and USB cable. The technology works by measuring how quickly acoustic signals travel along a length of pipe.
A technician first lowers a sensor onto a valve inside the valve chamber. A cable attaches the sensor to a white radio transmitter. Another technician repeats the process downstream with a sensor connected to a blue radio transmitter. The correlator connects the transmitters.
To listen for leaks, the technicians bleed a little water from a fire hydrant to introduce a vibration in the pipe. To check its structural thickness, they hammer against a hydrant outside the area spanned by the two sensors, then measure the sound velocity.
The correlator, connected to a laptop computer, calculates the acoustic velocity based on the sensor spacing and the time delay between the measured signals, then calculates the average wall thickness. “As the pipe loses material from corrosion, acoustic waves travel slower,” says Mitchell.
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Spikes displayed in the software interface mark the locations of leaks or weakened sections. To double-check the position, a technician wheels off the distance, takes the GPS coordinates, and photographs the spot so repair crews know exactly where to excavate. The team assesses five to 10 locations per day.
Information drives action
The 2007 condition report listed the average, maximum and minimum wall thicknesses. The worst section showed 70 percent deterioration with a nominal thickness of 1/2 inch and a measured thickness of 1/8 inch.
“We did more research on anything deteriorated beyond 45 percent or added them to our replacement list,” says Mitchell.
Additional research included checking soil conditions for metallic pipe settings.
“Our soils vary from mildly acidic to highly corrosive,” says Mitchell. “If we have pipe breaks in highly corrosive conditions and the assessment concludes some level of deterioration, we may do a destructive analysis on a pipe sample.
“Combining destructive analysis with acoustic assessment gives us a sound idea of when to replace the pipe and fully justifies funding for the project.”
Mitchell’s efforts to replace the right pipe at the right time helped reduce breaks. By 2010, there were six breaks. In 2011, there were two on the entire distribution system.