Corrosion is eating into the underground piping of three in four North American water utilities, and thousands of miles of aging steel and iron pipes are exacerbating the problem, according to a new study of the leaky system.
One possible solution: PVC pipe, which has the lowest overall failure rate when compared to cast iron, ductile iron, concrete, steel and asbestos cement, according to Water Main Break Rates in the USA and Canada: A Comprehensive Study, just published by the Utah State University (USU) Buried Structures Laboratory. The lab is one of just two in the U.S. that performs large-scale tests on buried pipes.
Utah State University
|The average age of failing water mains is 47 years old. Meanwhile, more than 8 percent of North America’s systems are beyond their useful life, and 22 percent are more than 50 years old.|
The purpose of the study was to compile and analyze the collective experience of nearly 200 utilities and 117,603 miles of pipe, to make future critical decisions about replacement, USU says. The research included comparison of water pipe failures to the pipe materials used.
Water main “break rates produce a compelling story which can aid our prudent decision making as it relates to repairing and replacing our underground pipes,” the report says.
Many Materials, One Decline
The report divides underground water infrastructure in North America into three main eras: the 1800s, 1900-1945, and post 1945. A variety of materials have been used in that time, as manufacturing technologies have evolved.
Ironically, however, “the life span of the materials used has become shorter with each new investment cycle” —particularly, newer ductile iron as compared to old cast iron—and all of the systems “will start to fail at nearly the same time over the next couple of decades,” the report notes.
More than 54,000 community water systems are facing pipe repair and replacement, the study says.
Among the report’s major findings:
• Corrosion is a major cause of water main breaks. Three-fourths of all utilities have corrosive soil conditions, and one in four main breaks is caused by corrosion.
• Failing water mains are on borrowed time. The average age of failing water mains is 47 years old. More than 8 percent are beyond their useful life; 22 percent are more than 50 years old; and 43 percent are between 20 and 50 years old.
Although pipe life is typically estimated at 100 years, the average real-life expectancy of pipe being installed in the ground today is 79 years. Pipes made of PVC and other non-corrosive materials, however, have an estimated life of more than 110 years, the study says.
• Pipe relining and other trenchless technologies will grow. More than 40 percent of utilities say they are considering pipe relining and pipe bursting, and 74 percent are considering directional drilling, a newer trenchless technology. Instead of digging a wide trench to lay pipe, a horizontal hole is made from an above-ground point, flushed with mud and drilling fluid, and then filled with a semi-flexible piece of fusible PVC pipe. One city engineer likened the technique to a needle going through fabric, with the ground as the fabric.
• Pipe material use varies by region, which accounts in part for vast disparities in failure rates. (Other factors include climate, installation practices, and soil corrosivity.)
The U.S. Northeast and North Central water systems are about 90 percent cast iron and ductile iron and are likely to see more breaks than other systems, the study predicts. Only 13 percent of utilities say they have avoided using ductile iron because of corrosion concerns. In Canada, PVC pipe makes up 43 percent of the total. Most utilities use several types of materials.
• Fewer people are being served than previously thought. While in urban areas, the industry has assumed 325 people are served for one mile of distribution system pipe, this survey suggests a new national metric of 264 people served per mile of pipe regardless of utility size.
Lessons in Napa
Napa, CA, is among the areas exemplifying the study’s future trends. The city has been working since January to replace a 7,400-foot stretch of corroded steel pipe with fusible PVC pipe using directional drilling (horizontal tunneling) rather than trenching.
Officials say that the method is far less invasive, expensive and time-consuming than opening up a conventional trench. A Napa Valley Register video shows the technology and materials in action.
The USU report is just the latest to sound the alarm about North America’s aging water infrastructure. In February, the American Water Works Association (AWWA) estimated the cost of addressing the U.S.’s buried drinking water infrastructure at $1 trillion over the next 25 years.
In 2009, the American Society of Civil Engineers issued a USA Infrastructure Report Card that gave a D- to drinking water and wastewater infrastructure.
And a 2001 report by AWWA concluded:
“Replacement of pipes installed from the late 1800s to the 1950s is now hard upon us, and replacement of pipes installed in the latter half of the 20th Century will dominate the remainder of the 21st.
“We believe that we stand today at the dawn of a new era—the replacement era—for water utilities.”