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Leaks and breaks within potable water piping infrastructures cause U.S. water utilities to lose more than a quarter of processed water between treatment plants and the tap every day. The large diameter (16 in. and larger) pipes that form the backbone of these systems primarily use steel, precast concrete cylinder, ductile iron, and PVC (polyvinyl chloride). Constant maintenance to keep the system at even this level of efficiency adds further costs to the equation. In fact, rehabilitating the potable water piping systems in the United States is estimated to cost more than $1 trillion over the next 10 years. The Water Research Foundation (WRF) and Environmental Protection Agency (EPA) have made it clear that there is a need for a more reliable and durable pipe material.
In 2015, the WRF in conjunction with EPA and others released a landmark report highlighting the use of high-density polyethylene in large diameter pipes. Specifically, the report outlined the efficiency and durability of large diameter HDPE pipes in water main applications. This article will provide a brief introduction to HDPE, share conclusions drawn from the WRF report, and highlight the latest large diameter pipe products in the United States.
An introduction to large diameter HDPE pipe
In the United States, most HDPE pipes are made of polyethylene (PE) resin PE4710, the North American analogue to the ISO PE100 resin. PE4710 is an ASTM standard that indicates, in order, the base resin density, the slow crack growth rating, and the hydrostatic design stress. Therefore, PE4710 has a density cell class of 3, a slow crack growth cell class of 7, and the maximum recommended hydrostatic design stress (1,000 psi) for water at 73°F. While PE100 is similar to PE4710, it is unique in that several subclasses have been introduced to tackle specific pipe designs. For instance, PE 100-RC possess high resistance to slow crack growth, meaning that the pipes won’t develop cracks at stresses less than their tensile strengths which also allows for PE pipe to be used with other installation materials other than just sandy conditions to ease installation. These pipes are also durable to chemical attack from the strong oxidizers used to disinfect drinking water, with lab reports stating that HDPE pipe made from PE100-RC resin can last in excess of 100 years under most water quality conditions. HDPE pipes are flexible or viscoelastic—a combination of being elastic- and fluid-like—which makes the pipe capable of relieving localized overstressing through small deformations.
Finally, most traditional piping systems are susceptible to leaks, which can add up to significant costs for many water utilities. With HDPE large diameter pipes, installers have the ability to fusion weld pipes and fittings to produce leak-proof pipe joints. For this reason, HDPE pipes have the lowest leakage costs among all other large diameter pipe alternatives.
Large diameter HDPE pipes for water main applications
Beyond the general benefits of HDPE pipes, the WRF report also surveyed existing water utilities that have used large diameter HDPE pipe. Most of the surveyed utilities responded that they were satisfied with the durability and reliability of HDPE pipe. The 5% who were unsatisfied, expressed concerns about tapping, repairs, joints, and permeation. These concerns were rooted in misconceptions of large diameter HDPE pipe, as there have been no reported failures due to oxidation or permeation using these piping systems.
Some surveyed also expressed concern about large diameter HDPE pipe’s performance under surge conditions. The report developed a specialized test to verify the performance of large diameter HDPE pipe under recurring surge conditions. The pipe was successfully tested with 2 million cycles of surge pressures between 125 psi and 188 psi, with no failures or leaks after six months of continuous testing. Additionally, the pipe was tested without failure for an additional 50,000 cycles at pressures between 125 psi and 250 psi.
Several case studies of the utilities implementing large diameter HDPE pipes were also cited. The studies revealed that utilities chose HDPE for large diameter transmission mains for its flexibility, fusible joints, corrosion resistance, compatibility with trenchless technology methods, and cost savings. For areas affected by earthquakes, HDPE pipe offers improved resistance to seismic conditions. To maximize cost savings and performance, correct construction techniques must be used to ensure the fusion of pipes and fittings.
The newest and largest class of large diameter pipes
The best way to ensure a proper fusion between pipes and associated fittings is to source both from the same manufacturer. AGRU America, an industry leader for over 70 years, now produces the largest diameter pipes and fittings in North America, extruding continuous pipe strings of up to 2,000 feet with outside diameter ranges between 24 and 138 inches. These large diameter pipes are well-suited for large-scale applications, such as water transmission mains. The state-of-the-art production facility is in full compliance with the strictest quality criteria according to ISO 9000 and ISO 14001 standards. As a result, AGRU XXL pipes and fittings meet and exceed both EN 12201 and ISO 4427 requirements. The facility is located on the Charleston harbor, allowing AGRU to extrude the large pipes directly into the water for towing to near- or offshore sites.