June 2012, Vol. 67 No. 6
Newsline
Water Main Break Study Released
The Comprehensive Water Main Break Rate Study for the United States and Canada compiles the collective experience of 188 utilities which can be used for making future critical pipe replacement decisions. Highlights of the Comprehensive Water Main Break Study include a new national metric for citizens served per one mile of pipe, aggregate data on pipe material break rates, analysis of age and corrosion in failure modes, and related observations on pressure, temperature and trenchless technology practices.
During 2011, Utah State University conducted a study of utilities across the United States and Canada to obtain data on water main failures of municipal and private water supply systems. The study was comprised of two parts: a basic survey and a more detailed survey. The focus of the basic survey was to examine the number of failures utilities were experiencing and how those failures related to the pipe materials used. This effort focused on water supply mains (sewer and force main pipes were excluded). A variety of pipe materials are used in water supply systems and over the past 100 years the materials have evolved with different manufacturing technologies. As a result, pipe performance has changed. A goal of the more detailed level of analysis was to look at which materials were performing best at a snapshot in time and to track how pipe age affects failure rates.
The study found that most utilities use several kinds of pipe materials with 80 percent of the installed water mains utilizing a combination of cast iron (CI) at 28 percent, ductile iron (DI) at 28 percent and PVC pipe at 23 percent. This fact is supported by a relative low amount (13 percent) of utilities which avoid DI due to corrosion concerns.
Water main pipe material usage varies significantly over geographic regions. The Northeast and North Central region of the U.S. use either CI or DI pipe for approximately 90 percent of its length. In Canada, PVC pipe makes up 43 percent of the total.
The study concluded that the water main break experiences of one utility may not represent another. Factors such as climate, installation practices and soil corrosivity can greatly affect failure rates. Every utility should properly install pipe, regardless of material used.
When failures rates of cast iron, ductile iron, PVC, concrete, steel and asbestos cement pipes were compared, PVC is shown to have the lowest overall failure rate according to the report.
It was concluded that corrosion is a major cause of water main breaks – 75 percent of all utilities have corrosive soil conditions and combined with a high portion of CI and DI pipes, one in four main breaks is caused by corrosion which is ranked the second highest reason for water main pipe failure. Northeast and North Central U.S. utilities will experience a higher percentage of corrosion breaks due to a higher concentration of CI and DI pipes (90 percent) installed.
Other findings include a new national metric of 264 people per one mile of pipe connections regardless of utility size. The average age of the failing water mains is 47 years old and 22 percent of all water mains are over 50 years old. The study also found that 8 percent of all installed water mains are beyond their useful life and the use of trenchless technologies will continue to increase with directional drilling as the most widely accepted technology with a higher satisfaction rating and 74 percent of utilities are considering it in the near future. This study contributes to the continuing efforts of the EPA’s Aging Water Infrastructure (AWI) research and the American Water Works Association (AWWA).
The Water Main Break Rates In the USA and Canada: A Comprehensive Study can be found at: www.neng.usu.edu/mae/faculty/stevef/UtahStateWaterBreakRatesLR.pdf
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