Issues in Leak Detection（III）

HOW THEY WORK

Acoustic leak detection offers a non-invasive detection method.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.(from valvemagazine)