HDPE Pipe Solutions for Water Infrastructure Rehabilitation
By Camille George Rubeiz, PE
“Water, water, everywhere/Nor any a drop to drink.”
–Samuel Taylor Coleridge, Rime of the Ancient Mariner
When English poet Samuel Taylor Coleridge wrote the above lines, he was describing the plight of a sailor stranded at sea—unfortunately, his prescient words are fast becoming applicable to the North American water supply infrastructure. In the United States, about 151.4 billion L (40 billion gal) of water is treated every day for domestic and public use, while about (300 billion gal) is employed for agricultural and commercial purposes.1 In most distribution systems, the amount of water lost or unaccounted for is typically 20 to 30 percent, but it can be as high as 50 percent for older systems.2 In addition to the apparent loss of water and damage to pipe network (i.e. bedding erosion and pipe breaks), leakage can also become a public health issue due to contaminants entering the pipe through openings when water pressure in the distribution system is lost.
Pipe dreams and nightmares
According to the American Water Works Association (AWWA), leaks in individual main water lines can reach up to 3785 L (1000 gal) per minute, while valve leaks can reach up to 1893 L (500 gal). Leaks due to corrosion are the worst culprits and the hardest to detect because they usually start out small as a result of excessive pressure, improper installation, settlement, or overloading. Main line and valve leaks progressively worsen until they become significant problems. At up to $800 per mile of main line, the cost of their detection is both expensive and time-consuming.
Total replacement of the approximately 3.2 million km (2 million mi) of water pipe inventory in the United States—not forgetting the additional 965,606 km (600,000 mi) of wastewater pipe and the 112,000 km (69,594 mi) of Canadian water mains—would be expensive, disruptive, and protracted, to say the least. Given the problem’s enormity and complexity, utilities are scrambling to develop alternative water and wastewater pipeline rehabilitation strategies. The remedy currently gaining the most traction is ‘trenchless technology.’ Central to this approach is the selection and use of virtually leak-free, high-density polyethylene pipe, also known as HDPE pipe.
Trenchless technology is the use of non-intrusive construction methods, materials, and equipment for the installation, replacement, or rehabilitation of underground pipe infrastructure. It has recently gained favor with utilities and their customers, partly because it is quicker and less socially disruptive than open-trench construction, but mostly because it can take full advantage of recent advances in the development of long-lasting HDPE pipe.
Polyethylene possibilities
High-density polyethylene pipe is usually produced in straight lengths up to 15 m (50 ft) long and coiled in diameters up through 152 mm (6 in.). The material neither tuberculates nor supports bacterial growth. As such, HDPE pipes have excellent chemical resistance and are suitable for even harsh environments. Given the Federal Highway Administration’s (FHWA’s) estimation utilities annually spend $36 billion on protecting pipes from corrosion, it is also important to note polyethylene is dielectric (i.e. non-conducting), which means it is not subject to corrosion and maintains its flow capability over time. While the Hazen-Williams C Factor of other materials is dramatically reduced over time due to corrosion and/or tuberculation, HDPE remains constant at 150.
Although many different types of plastic pipe share these particular advantages, HDPE pipes and related products combine these attributes with the added benefits of heat-fused joints and flexibility.
Heat fusion
HDPE pipe offers excellent fusion integrity, enabling the development of one continuous pipeline system. Heat fusion, the process of joining pieces of pipe to each other or other elements (e.g. valves), produces fully sealed connections. This can eliminate the potential leak points that could come every 3.1 to 6.1 m (10 to 20 ft) with other materials and fixtures.
The life-cycle cost of HDPE pipe can differ from other materials because the allowable water leakage is zero, rather than the typical leakage rates of 10 to 20 percent for conventional counterparts. HDPE pipe’s fused joints are self-restraining, thereby eliminating costly thrust restraints or thrust blocks. Furthermore, HDPE pipe’s fused joints virtually never leak, effectively eliminating infiltration and exfiltration problems experienced with alternate pipe joints.
The high density polyethylene pipe industry conservatively estimates the service life for HDPE pipe to be between 50 and 100 years. Potentially, this can relate to savings in replacement costs for generations to come.
Flexibility
HDPE pipe can provide greater durability and flexibility than certain other materials because it can be easily bent into place and pulled through existing pipes. HDPE pipe can be reshaped to a radius 25 times the nominal pipe diameter. In other words, 305-mm (12-in.) HDPE pipe can be cold-formed in the field to a 7.6-m (25-ft) radius, which can eliminate the many fittings required for directional changes in a piping system.
The flexibility of HDPE pressure pipe makes it well-suited for dynamic soils, including areas prone to earthquake. It can accept repetitive pressure surges significantly exceeding the static pressure rating of the pipe. Its combination of flexibility and leak-free joints also allows cost-effective installation methods such as horizontal directional drilling (HDD), pipe bursting, sliplining, and plow and plant.
Additionally, since polyethylene is far less dense than other materials, it does not demand the use of heavy-lifting equipment for installation. Nevertheless, HDPE pipes can structurally withstand various types of impacts, especially in cold-weather situations where other materials can be more prone to cracks and breaks.
Notes
1 See the American Water Works Association (AWWA’s) Web site at www.awwa.org, and search for “25 Facts About Water.”
2 National Research Council (NRC) of Canada’s “Detecting Leaks in Water-Distribution Pipes,” Construction Technology Update (No. 40, October 2000). Visit irc.nrc-cnrc.gc.ca/ctus/ctu40e.pdf.
About the Author
Camille George Rubeiz, PE, is the director of engineering for the Plastics Pipe Institute (PPI), and is a member of the American Water Works Association (AWWA), the American Society of Civil Engineers (ASCE), and the American Society of Plumbing Engineers (ASPE). He can be contacted via e-mail at crubeiz@plasticpipe.org.
Specifications and Standards
High-density polyethylene (HDPE) solid wall pipe has been used in potable water applications since the 1960s. While the American Water Works Association (AWWA) is expected to publish its AWWA M 55, Manual for the Design and Installation of Polyethylene Pipe in Water Applications later this year, the material is currently specified and/or approved in the following standards:
- AWWA C 901-02, Standard for PE Pressure Pipe and Tubing, [13 through 76 mm] 0.5 in. through 3 in. for Water Service;
- AWWA C 906-99, Standard for PE Pressure Pipe and Fittings, [102 through 1600 mm] 4-in. through 63 in. for Water Distribution and Transmission;
- ASTM International F 714-03, Standard Specification for PE Plastic Pipe Based on Outside Diameter;
- ASTM D 3035-03a, Standard Specification for PE Plastic Pipe Based on Controlled Outside Diameter;
- ASTM D 2657-03, Standard Practice for Heat Joining Polyolefin Pipe and Fittings;
- ASTM D2683-98, Standard Specification for Socket-Type Polyethylene Fittings for Outside Diameter-Controlled Polyethylene Pipe and Tubing;
- ASTM D3261-03, Standard Specification for Butt Heat Fusion PE Plastic Fittings for PE Plastic Pipe and Tubing;
- ASTM D3350-02a, Standard Specification for Polyethylene Plastic Pipe and Fittings Materials;
- ASTM F1055-98e1, Standard Specification for Electrofusion Type Polyethylene Fittings for Outside Diameter Controlled Polyethylene Pipe and Tubing;
- Canadian Standards Association (CSA) B 137.1-2002, Polyethylene Pipe, Tubing, and Fittings for Cold-water Pressure Services;
- NSF International/American National Standards Institute (ANSI) 61-2003e, Standard for Drinking Water Systems Components—Health Effects; and
- NSF/ANSI 14-2003, Standard for Plastics Piping System Components and Related Material.
A Brief History of HDPE Pipe in U.S. Water Infrastructure
1948: First high-density polyethylene pipe systems made available.
1955: ASTM International establishes the Plastic Pipe Committee
1978: American Water Works Association (AWWA) approves HDPE pipe for water tubes up to 75 mm (3 in.) in diameter.
1990: AWWA developed first edition of AWWA standard for HDPE water pipes ranging in diameter between 100 and 1575 mm (4 and 63 in.).
1992: Indianapolis Water Co. (now U.S. Filter) adopts the technology, making Indianapolis, Indiana, one of the first municipalities in the United States to install water mains using HDPE pipe.
2005: Expected release date for AWWA M 55, Manual for the Design and Installation of Polyethylene Pipe in Water Applications
For more information on specifying and using HDPE pipe systems, visit the Plastic Pipe Institute (PPI) Web site at www.plasticpipe.org, and select ‘Applications,’ followed by ‘Water.’
Crossing the Canal with HDPE Pipe
Emanuel Gottlieb Leutze’s famous 19th Century painting, George Washington Crossing the Delaware, is an impressive technical and artistic achievement. On a very different scale, The Artesian Water Co.’s recent navigation of the river’s attached waterway is also quite remarkable.
To help integrate previously separated portions of its supply system, the company needed to cross the canal running from the Delaware River into the Chesapeake Bay near the Port of Baltimore, Maryland. Being able to successfully traverse the 137-m (450-ft) wide channel—which runs 10.7 m (35 ft) deep—called for the specification of high-density polyethylene (HDPE) pressure-application water pipe.
The project, intended to add redundancy to Artesian’s potable water and fire protection service capacity, required the installation of 1524 m (5000 ft) of 610-mm (24-in.) HDPE pipe, using two 762-m (2500-ft) directional drills. Working on a tight timeline, contractors finished the work between January and June 2004—despite the added challenge of a 45.7-m (150-ft) drop in elevation from the land-based water main to approximately 15 m (50 ft) below the bottom of the Chesapeake and Delaware Canal.
“Our standard water pipe material for crossing large bodies of water or for use in corrosive soils is HDPE,” says project manager Adam Gould “This was the biggest project of its kind we’ve done—because of its flexibility, HDPE was the only pipe we would have used to do it.”
International consulting, engineering, construction, and operations firm, CDM Inc., was responsible for charting the HDPE pipe’s course with design drawings and working with the canal’s owner, the US Army Corps of Engineers (USACE), on the proper permits. According to CDM’s vice president, it was the HDPE pipe’s combination of flexibility and leak-free, heat-fused joints that allowed the unique construction methods employed.
“The directional drilling with HDPE pipe is conducive to minimizing disturbances during the project,” said Bill Cesanek, AICP.
Nuclear Winner
At the U.S. Department of Energy/National Nuclear Security Administration’s (DoE/NNSA’s) Pantex Plant near Amarillo, Texas, a leak in the water piping can be a matter of large-scale life or death.
Melvin Suttle, the high-pressure fire loop system engineer at BWXT Pantex, the plant’s management and operating contractor, noticed pipe breaks due to corrosion of the cast and ductile iron system (first installed in the late 1940s). The 24,079-m (79,000-ft) long high-pressure fire loop is a dedicated water distributor feeding fire suppression systems, which can be seriously compromised by a bad break.
In August 2001, he specified 18.3 m (60 ft) of high-density polyethylene pipe for extending a system requiring 19 m3 (5000 gal) per minute and 18 kg (40 lb) of residual pressure.
“Back then, the product was brand new to us,” Suttle said. “It’s performing very well. And knowing what I know about HDPE pipe now, I’m sure we’ll never have to see that 60-foot section of pipe again.”
Today, Pantex has about 1189 m (3900 ft) of HDPE installed for the high-pressure fire loop, and a phased plan to replace an additional 15,240 m (50,000 ft) with the material. However, the transition required numerous steps and hurdles before Suttle received his approvals.
“My impression is HDPE pipe was viewed by some site engineers as low-quality material to be used for temporary service,” he says. “I worked with my management to have vendor demonstrations on site. This was no small task due to site security. I also collected all the vendor data I could find using the Internet extensively, conducted visits to municipalities and observed [other materials] and talked to several installers.”
Since the high-pressure fire loop is considered ‘safety-class,’ any proposed changes must be defined, described, and proven to meet the operating requirements of the system. In fact, a DoE engineer objected to the use of HDPE pipe before Suttle proved the material was listed in National Fire Protection Association (NFPA) 24, Standard for the Installation of Private Fire Service Mains and their Appurtenances.
Suttle was also able to successfully argue the HDPE pipe material would be a strong environmental choice, as its fused joints minimize the possibility of contaminants leaching into the water supply. HDPE was also ideally suited to the horizontal directional drilling (HDD) installation needed to run the pipe under two railroad tracks, a roadway, and a security corridor.