Alabama City Uses Leak Detection Survey on Large-Diameter Pipes
Aug 21, 2013
Aging infrastructure across the United States is a major obstacle facing utilities. With pipe failures increasing and becoming more publicized, utilities are facing increasing pressure to rehabilitate or replace their critical water and wastewater infrastructure. Industry reports also paint a daunting picture about the state of U.S. infrastructure, with The American Society of Civil Engineers 2013 Report Card on America’s Infrastructure estimating that the costs surrounding infrastructure renewal range from $200 billion at the lowest to $1 trillion over the next 25 years.
Lost in the topic of infrastructure renewal is the amount of water that is unaccounted for each year due to leaks on archaic water pipelines. While most of the discussion surrounds pipe failures and possible financial options for renewing the nation’s infrastructure, between 15 and 20 percent of all water pumped by utilities in the United States never reaches the tap. This number is as high as 60 percent in some municipalities, according to the U.S. Environmental Protection Agency. This number not only represents a huge financial loss, both in the value water and the energy that is needed to treat and pump it, but the loss of a critical natural resource.
In many cases, an infrastructure management program that addresses leaks on large-diameter water transmission mains is the first step to an overall infrastructure renewal plan. Early identification and repair of leaks allows utilities to reduce lost water revenue and prevent pipeline failures, as leaks are often an early signal that a pipeline will eventually rupture. Completing regular leak detection surveys also provides important information about the baseline condition of a pipeline and can act as a prescreening function in determining a more comprehensive condition assessment plan.
Although leaks on small-diameter distribution pipelines are the most common form of leak a utility encounters, leaks on large-diameter transmission pipelines are of greater importance in maintaining safe and reliable service delivery. Because large-diameter leaks are less common, they often go undetected for long periods of time resulting is massive water losses. Identifying small leaks early on can prevent years of undetected leakage and stop leaks from increasing in size over time; by the time a large leak is identified, it has likely been leaking for many years and is in the tail-end of its life.
A study completed by The American Water Works Association showed that while leaks on large-diameter pipelines make up less than 5 percent of the total number of leaks, they account for more than 50 percent of the total water lost from leaks. This is primarily because transmission mains are often several times the size of distribution mains and carry water at a much higher capacity and operating pressure than distribution pipelines. By focusing leak detection programs on large-diameter pipes, a utility can achieve a large reduction in Non-Revenue Water by identifying and repairing even one leak on a major pipeline.
In early 2012, the Birmingham Water Works Board (BWWB) ran a successful leak detection program on 7.7 miles of 42-in. Reinforced Concrete Pipe (RCP) that transports water from Shades Mountain Filter Plant to different areas of the city. The inspected pipeline was constructed in 1927 and has a typical operating pressure between 60 and 90 psi.
BWWB completed the inspections in order to proactively address leakage on its critical large-diameter pipelines, as well as identify and repair suspected leaks on the 42-in. pipeline.
The survey was completed in three separate inspections and was successful in locating 26 leaks of varying size with close location accuracy. Twenty of the leaks have since been verified and repaired by BWWB, while the remaining six leaks have been deferred due to their size or matched up with existing features.
In order to ensure a successful project, BWWB planned the project thoroughly in order to achieve optimal conditions for the technology. This included review of drawings and flow management, as well as strong communication with the consulting firm, Pure Technologies.
BWWB used SmartBall leak detection for the inspections. The tool is a free-flowing leak detection platform that operates while the pipeline remains in service. It is capable of completing long inspections in a single deployment and is equipped with an acoustic sensor that identifies acoustic anomalies associated with leaks; the acoustic signature is then analyzed to determine if it is a leak, air pocket or an external noise.
To track the tool as it traverses the pipeline, receivers are placed strategically throughout the planned inspection route. As the tool traverses, it makes a sound that is recorded by the receivers to determine its position on the pipeline; this system allows leak locations to be estimated typically within 10 ft of the actual leak location.
BWWB’s survey using SmartBall was able to detect several leaks that were as small as 1 gallon per minute to as large as 15 gallons per minute. This allowed BWWB to make informed repair decisions for each identified leak, allowing for the short-term deferral of some small leaks in favor of the larger leaks.
Many leak detection programs have a mandate to save the most water, and therefore focus only on locating the large leaks. However, locating small leaks is an important part of a leak detection program.
In terms of reducing Non-Revenue Water, small leaks may actually represent the best opportunity for long-term water loss reduction. Leaks on large-diameter pipelines typically form and mature over a period of decades. Locating and repairing a large leak prevents it from leaking for the “tail end” of its life, and from failing catastrophically. Catching a leak while it is very small does this as well, but also prevents the decades of sustained water loss that would occur as it grows into a large leak.
Through the location of both small and large leaks in its 2012 survey, BWWB was able to repair high priority leaks, but also identify the small leaks that can be repaired to prevent long-term water loss. The project has provided BWWB with valuable information moving forward with the management of its large-diameter pipeline system. In summer 2013, BWWB will complete additional inspections on a critical raw water pipeline using advanced inline leak detection methods.
Birmingham Water Works Board operates the largest water system in Alabama serving approximately 600,000 customers over 33 municipalities. It includes 3,900 miles of pipe and pumps 102 million gallons per day.
Stephen Rothwell is a marketing specialist with Pure Technologies.
1Saving Water, Saving Money in the Gwinnett County, Georgia, Department of Water Resources
Olson, Eric W.; Henderson, James C. American Water Works Association /