Clamping down on leakage in flat terrain, saves water and power consumption
Submitted by Echologics.
Ongoing leaks can waste a lot of energy, resources and money, especially on flat terrain where municipal pumping is required to keep the system pressurized and where water is purchased from a local municipal purveyor at retail rates. Mueller Water Products was recently hired by an energy performance firm to survey a federal government water distribution network in Ontario to determine if leakage was contributing to unnecessary energy consumption.
Approximately 46 kilometers (28.5 miles) of water mains were surveyed using EchoWave® acoustic leak detection to noninvasively detect and pinpoint leaks. Echologics® field technicians set up 222 access points on pipes, valves and hydrants to attach LeakFinder-ST™ leak correlator sensors. The sensors listen for noise created by a leak. If a leak is detected, the technology uses the distance and time delay between sensors to accurately determine the position of the leak.
The leak detection survey was conducted on pipes across the network, consisting of various materials, most of which were cast iron and polyvinyl chloride (PVC), ranging from 150 to 400 millimeters (6to 16 inches) in diameter. For metallic mains, the sensors were attached magnetically to valves. For PVC pipes, technicians used hydrophone sensors mounted to the side port of fully charged fire hydrants for elevated acoustic sensitivity. The sensors were connected by cable to a transmitter, which communicated with a receiver at the technician’s computer. The acoustic data was processed on-site to determine if there was evidence of a leak. Several criteria must be met for audio recordings to provide a positive leak detection result. This includes, but is not limited to, a clean, distinctive correlation peak, an observable coherence level, a similar frequency spectrum in each channel and/or a minimum amount of clipping in the time signal. The water main leak had all these indications.
A total of seven leaks — including hydrant, service piping and water main leaks — were identified, and one leak on an 8-inch water main was significantly large. Given that the size of this water main leak was identified to be large, the Echologics team was on-site during the leak excavation and repair activities. This leak detection team was able to confirm the leak position between two fire hydrants as being approximately 23 meters (75 feet) from the second hydrant, reconfirming the original position reported.
The graph below shows the positive correlation and frequency profile of the leak.
Upon excavation, it was determined that the circumferential crack on the 200-millimeter (8-inch) cast iron water main had an average width of approximately 3 millimeters (1/8 inches) and covered over 50% of the circumference of the pipeline. The crack was determined through visual observations as actually being slightly less than 3 millimeters (1/8 inches) wide at the edges, but approximately 6 millimeters (1/4 inches) wide at the bottom of the pipe. The average 3-millimeter-wide (1/8 inch) crack was believed to be a conservative average estimate for the entire crack length.
The leak was repaired utilizing a stainless-steel repair clamp, which is a standard repair for this type of leak. The water main did not show signs of severe or widespread corrosion. The following day, Echologics crews returned to the site to complete a post-leak repair investigation to confirm that no additional leaks were present, and the correlator confirmed that the repair was successful.
Big leaks are costly — consider permanent leak monitoring
The actual leak flow rate of the leak was between 750 and 1000 LPM (198 to 264 GPM). The cost of a leak this size is close to CAD 1 million a year, which is a large enough number to justify a regular leak monitoring program. Large leaks can consume a significant amount of energy by continuously pumping water to maintain desirable water pressure. This also puts unnecessary wear on pumping equipment that is used to keep water flowing that never makes it to the tap.
The other six leaks are also being repaired. The absence of leaks within the remaining water mains is not necessarily indicative of good pipe wall condition. Therefore, recommendations were put forward to assess the condition of the remaining water pipes, considering the consequence of failure and other potential issues, such as low pressure or poor water quality complaints. In addition, a regularly scheduled leak detection survey was recommended as a relatively inexpensive option for finding leaks within the system.
As water mains are often buried deeper in Canada than in many other parts of North America, leaks are less likely to surface and can go undetected for several years. As the main artery of the water distribution system, water mains transport huge volumes of water and are often under higher pressure to meet demand over long distances. Consequently, when a leak does occur, the volume of water loss is often greater than on smaller pipes. The best solution for water mains is a permanent leak monitoring system that can find most leaks on a pipeline, including small leaks before they turn into catastrophic failures.
Consider the EchoShore®-DX, a fixed leak detection technology using proprietary acoustic sensors, to find leaks on a wide variety of pipe materials and water distribution mains, including those in flat terrain. Sensors identify extremely faint acoustical noises emitted by leaks before they become detectable by conventional methods. Sensors can attach to valves, boundary boxes or hydrants so utilities can get coverage where they need it.
