Previously published in Plastics Engineering and posted with permission from the Society of Plastics Engineers.
This is the first of two articles on plastic pipe. The next article will focus on PVC pipe.
There is a lot of conversation about water these days. Whether it’s managing through droughts, worrying about contaminants, or balancing urban and agricultural needs. And one topic—our aging water infrastructure—is likely to get even more attention because the pipes that deliver fresh drinking water and carry away wastewater in many U.S. towns and cities are old and leaking, wasting precious resources.
Each day there are hundreds of water main breaks in the United States, resulting in expensive repairs that can tie up entire neighborhoods and clog traffic. And each day billions of gallons of water are lost from U.S. drinking systems during transmission. The American Water Works Association analyzed data from a sample of water utilities and found that water loss (typically measured as water that is generated but not paid for) varied from seven percent to 45 percent, averaging nearly 27 percent.
So according to this study, more than a quarter of water transferred never makes it to the customer. If these same percentage were applied elsewhere, in theory, a state like California could meet its mandated 25 percent water use reduction simply by preventing this average amount of water loss.
Replacing decaying pipes
While not all of this water loss is due to faulty water transmission, aging pipes contribute significantly. Decades old lead, cast iron, steel, and cement pipes remain prevalent, and replacing them is a hugely expensive and disruptive affair. The U.S. Environmental Protection Agency says it will cost $384 billion over 20 years simply to maintain the existing drinking water infrastructure. Replacing and expanding it to keep up with population growth could cost as much as $1 trillion. In the absence of upgrades, infrastructure failures will seriously disrupt water service, transportation, and commerce.
One question is: replace the infrastructure with what? The traditional materials that today are breaking down daily? Or advanced materials that can be more effective and last longer?
That’s where plastics could play a huge role, a role they already have begun.
Plastic pipes, of course, are commonplace today, have replaced traditional materials in many applications, particularly households. But technologies now allow plastic pipes to replace existing aging pipes without necessarily removing them, technologies that can dramatically reduce the cost and disruption of repairing and upgrading the water infrastructure. To demonstrate this advance, let’s take a look at a pipe replacement project in one of the U.S.’s most honored sites: Arlington National Cemetery.
Arlington National Cemetery
The final resting place for many of America’s soldiers, Arlington National Cemetery rests on rolling Virginia hills across the Potomac River from the District of Columbia, a site that provided a strategic high ground position during the Civil War. The curving pathways throughout the cemetery conform to the natural topography, and they are lined with stately flower gardens and majestic trees.
More than 60 years ago, a series of cast iron water pipes were installed for fire suppression and other water use. The water pipelines snake around seventy sections of the cemetery, as well as up and down the hillsides. When time came to replace these aging pipes, great care was needed not to disrupt the serenity and operations of a cemetery that needs to remain open for the average 11,000 visitors per day and multiple daily military funeral processions.
So instead of digging large trenches throughout the cemetery to remove old pipes and lay new pipes, engineers utilized pipe bursting technology that inserts high-density polyethylene plastic pipe into the existing pipe space. Small pits were dug on either side of the old pipe needing replacement. A metal bursting head attached to the replacement plastic pipe was placed in the pipe opening. From the other opening, the bursting head and pipe were pulled through the existing pipe space, leaving the new pipe in its place.
By repeating this process, engineers replaced more than 44,500 feet of existing cast iron water mains with long lasting plastic pipes. This process satisfied the need to retain environmental and operational integrity of the cemetery—it even occurred many times near high profile areas such as former President John F. Kennedy’s grave and the Tomb of the Unknown Soldier with its hourly changing of the guard.
Traditional water pipes usually are laid in sections in a series in large trenches and then joined from above ground to form long pipes. Pipe bursting typically employs a more advanced process called butt fusion.
As a section of plastic pipe is pulled through the existing old pipe, another pipe section is fused to it on site. To accomplish this, the two pipe ends are scraped clean and then pressed against a heater plate that heats the ends of the pipes. Once the plastic reaches the appropriate temperature, the heater plate is removed and the ends of the pipe are forced together, which fuses the two pieces together into a monolithic system in a short period of time. The new length of pipe is then pulled through the old pipe, and this process is repeated until the newly joined long plastic pipe reaches the length of the pipe it’s displacing.
In addition to pipe bursting, a similar technology uses plastic pipe to replace older failing pipes. As an example, Washington, DC, installed 402 feet of pipe on busy 16th Street… overnight. Instead of pipe bursting, contractors inserted 30-inch plastic pipe inside a failed 36-inch metal pipe in a process called slip lining. The smaller diameter pipes were butt fused and slipped inside the larger pipe. And morning commuters were not disrupted.
So… engineers were able to replace the water pipes at a national cemetery with hills and winding paths and revered structures. Fortunately, that same process can translate directly into towns and cities across the country. This technology is making inroads, saving communities time, disruption, and expense. Some communities, such as Palo Alto, CA, have been replacing aging conventional pipes with plastic pipes since the 1990s. After year of success, today more and more communities are turning to the benefits of this type of pipe:
- It’s tough and flexible, so it can be bent around cul-de-sacs and pulled through 2,500 feet of existing pipe;
- The systems are designed to resist corrosion and provide years and years of reliable service;
- Communities often can install these systems more economically than traditional systems;
- The pipes are well suited to areas prone to earthquakes or floods, due to their inherent flexibility and impact resistance; and
- As previously mentioned, “trenchless” technology allows the pipe to be pulled into the aging pipe with little surface construction or disruption.
Of course, there are many other types of plastic pipes that benefit the U.S. water infrastructure. As communities throughout the U.S. struggle with managing and upgrading a decaying infrastructure, it’s likely that plastic pipes of all kind will play an ever-increasing role in delivering water safely.