To pinpoint leak location and isolate areas of a pipeline for leak repair, utilities managers need to know valve locations, how valves operate and the condition of those valves. This article looks at why leak detection is critical, explains why valve location and condition assessment is vital and introduces new technologies that can determine the overall condition of water pipelines.
THE WATER SITUATION
The deteriorating condition of the nation’s water infrastructure is well-documented. Findings in the American Water Works Association (AWWA) State of the Industry Report 2011 suggest that water utility budgets will continue to be tight in 2013. That report, which is based on responses from nearly 2,100 water industry professionals, found that only 11% of respondents felt their existing plans will cover infrastructure funding needs and nearly a quarter felt that less than 20% of their needs will be met.
Water leaks and main breaks are steeply increasing in frequency as years of unchecked deterioration take their toll on a water infrastructure that, in places, dates back to the second half of the 19th century.
For example, in February 2011, news outlets reported that Kansas City, MO, experienced 467 main breaks in that one winter—a 73% increase from 2010. Montgomery and Prince George’s Counties in Maryland also made news headlines that year for major breaks in their water systems, which deliver service to 1.8 million people. Both counties set a record in December 2010 for having the largest number of water main breaks in a single month—647. The very next month, Prince George’s County experienced a 54-inch water main break that leaked an estimated 50 million gallons of water. These kinds of stories show why 15-30% of treated potable water that is lost—is lost through leaks.
In addition to these high profile water main breaks, recent studies by American Water indicate that the average leak runs undetected for more than six months before it surfaces. Leaks on larger transmission mains may never surface, and many instances have occurred where large leaks result when water finds a path of escape, resulting in a problem going undetected until catastrophic failure of a main.
Valve assessment is an essential component of effective distribution system management. Malfunctioning, closed, “frozen” and valves lost in the system make isolating a specific area of distribution for emergency or routine repairs difficult, time consuming and on occasion, impossible.
Initial distribution system valve assessment followed by annual system-wide valve maintenance enhances a utility operator’s capability to effectively control the flow of water within the distribution system. Assessment and maintenance also prolong the life of valves and ensure that those valves can be located, accessed and operated when needed. Assessment also allows a utility to better plan and schedule system repairs and improvements. Assessing valves and identifying their exact location on a geographic information system can help utilities’ reaction times and limit damage to surrounding infrastructure in the event of a water main break.
Historically, leak noise correlators, while effective on small-diameter metallic mains, have had difficulty doing the jobs for plastic and large-diameter transmission mains. They’ve also been difficult to operate, and training has concentrated more on equipment instruction than learning how to effectively find leaks. Leak detection equipment traditionally provides information only about the current state of the pipe with no information on the overall condition of the infrastructure.
However, advancements in acoustic leak detection and pipe condition assessment methods now help utilities to cost-effectively and efficiently detect leaks in difficult pipe types such as plastic. They also can help prioritize water system repairs and replacement without breaking ground or disrupting service. These new methods rely on measuring how quickly an acoustical signal is transmitted along a section of pipe using vibration sensors and acoustic correlators. The process is completely non-invasive; devices are attached to a section of pipe using standard appurtenances such as valves, hydrants or direct attachments to the pipe’s outer wall.
HOW THEY WORK
An acoustic signal is induced into the pipe and changes to the signal, specifically changes to its transmission or propagation velocity, can be related to changes in pipe wall structural integrity. This yields a highly accurate measurement of the remaining (or effective) structural integrity of selected pipes while simultaneously detecting and locating leaks. Also, because of advances in sensor designs and signal processing technologies, significant improvements have been made in the ability of such systems to resolve leak noise in the presence of ambient background noise often created by running water, traffic or pumps. Because of all this, utilities can detect leaks and assess the condition of pipes of all sizes and materials—including ductile and cast iron, concrete, plastic and asbestos cement—as well as pipes that are located in noisy, high-traffic environments.
The use of such technology is increasing among water service providers across North America and in Europe, South Africa, Singapore and Australia because of its accuracy and cost advantages over traditional methods.
A recent example of how this works can be seen at the Sewerage and Water Board of New Orleans (SWBNO). Following Hurricane Katrina, SWBNO adopted an acoustic-based pipe condition assessment system that helped to reduce water loss and efficiently prioritize replacement of pipes based on the extent of deterioration of those pipes. As a result, the city has been able to pinpoint water main leaks and measure the remaining wall thickness of pipes without having to undergo expensive and disruptive excavations. The SWBNO credited this process with locating numerous leaks in its mains that were causing between 75,000 and 100,000 gallons of water loss per day (the equivalent to filling one Olympic swimming pool every six days).
The Las Vegas Valley Water District (LVVWD) is taking a similar approach. While this district has a relatively young water infrastructure that experiences very few main breaks per mile as compared to other major utilities, some of its pipes have started to fail. A particularly troublesome section of pipe was part of a 6.5-mile span of 16- to 36-inch mortar-lined, steel cylinder pipeline that ran underneath some of the city’s most popular thoroughfares.
The pipe was installed in the 1950s without any cathodic protection or corrosion control and had experienced three main breaks over a five-year period. LVVWD expected to have to replace the entire span of pipe—a major expense that could have cost as much as $300 per foot while disrupting busy roadways. However, using non-invasive acoustics, the entire six and a half miles was surveyed in only two weeks and LVVWD found that the majority of the pipeline was still in good structural condition. Rehabilitation money was then prioritized to areas with the greatest need.
While constrained budgets continue to present difficult challenges for utilities, they have alternatives that mean they may not have to place efforts to reduce water loss and prioritize repairs on hold. Non-invasive acoustics can provide those utilities an alternative to the expensive and time-consuming processes associated with traditional leak detection methods.