The Environmental Argument for Plastic Piping
by Melissa Grace

common fallacy is that all plastics are bad for the environment. Another common fallacy is that all plastics are disposable, because the first thing most people think of when they hear “plastics” is what we would consider single-use plastics such as plastic bags, bottle holders, plastic cups and other similar products that often end up in landfills or in our oceans, taking many years before they degrade. But those very properties are also found in the plastics that have been used to protect our environment.

We should not demonize and remove such a versatile material as plastics from any conversation regarding our environment. Plastics have been used for decades to protect our environment. Geosynthetics, a class of plastics used to stabilize the terrain and solve numerous civil engineering problems, are one example. Geosynthetics have been used in landfills as a means for containment, protection, separation and filtering. Without these materials, leachate generated from water seeping into a landfill can get into our groundwater, ruining ecosystems and our drinking water.

Plastics can also be used as a construction material for other essential infrastructure such as piping for water, wastewater and gas systems. This article provides the environmental argument for using plastics as a piping solution, including performance and durability, life cycle assessments and their true costs compared with other materials and recyclability.

Improved performance with HDPE pipe
In the 2021 infrastructure report card by the American Society of Civil Engineers, piping infrastructure responsible for drinking water, wastewater and stormwater scored C or lower (1). The report makes several recommendations for how we can improve our infrastructure grade. At the top of the list are extending the lifespan of our systems, improve efficiencies, reduce waste and improve resilience to risk events such as changing climate patterns. One of the report’s biggest findings is that most wastewater treatment systems are designed to last between 40 and 50 years, which is about half of what engineers typically aim for in many other infrastructure projects. If we are to improve U.S. piping infrastructure, which plays an enormous role in protecting our environment, then the first step is choosing a different piping material.
An approximate 3,100 ft 54″ OD SDR 11 AGRU HDPE pipe was used to create a new force main at Fort Lauderdale, FL, USA, making it one of the longest and large horizontal directional drill pressurized sewer pipe installations in the world.
High-density polyethylene (HDPE) is a great material for piping systems for many reasons. First, consider its performance. HDPE pipes have low-permeability built-in, minimizing leakage and waste. These pipes are also quite chemically stable, meaning that they do not react with many of the compounds often found in wastewater systems that can lead to microbial-induced corrosion (MIC) that affects concrete pipes. HDPE pipes are also durable and flexible, which allows installers to use low-impact installation methods such as horizontal directional drilling (HDD). HDD offers the ability to avoid lengthy disruptions and can help bypass ecologically sensitive locations. These pipe’s durability and flexibility also means some measure of protection against seismic events (2). Finally, HDPE pipes are homogenous — made with only HDPE — and the leakage rate is minimal to none.

The problem with infrastructure development often comes down to upfront cost. How can lawmakers create solutions that not only solve our infrastructure problems, but also remain cost-effective in the long term? With HDPE, highly durable and long-lasting piping systems can be created that not only last for 100 years, but also require very little maintenance. But exactly how does HDPE stack up to competing piping materials?

Many AGRU HDPE pipe
Many AGRU HDPE pipe fittings are made with PE 100-RC, an HDPE resin variant with enhanced stress crack resistance, supporting even lower SDR to withstand higher pressures.
Life cycle assessment of HDPE pipes
A recent life cycle assessment of stormwater piping systems in North America compared the environmental impact of several piping materials including HDPE, PVC, reinforced concrete pipe and steel. The study looked at factors such as impact to global warming, acidification, eutrophication, ozone depletion and smog formation as well as total energy demand and waste. In this study, HDPE pipes outperformed the other materials in categories such as global warming, acidification, eutrophication, ozone depletion and smog formation. Additionally, HDPE pipes produced the least amount of solid waste and used the least amount of water (3).

It is also important to mention that due to their nonreactive surfaces, HDPE piping systems do not corrode, rust, rot, pit, tuberculate or support biological growth. These properties make the material ideal for long-term projects such as wastewater systems because it does not need to be replaced or maintained in the same manner as other materials. Another benefit is that piping systems made with HDPE cost less energy to operate. In the water flow equation, the water velocity is affected by several variables including the roughness coefficient, denoted as C, which refers to the smoothness of the inner surfaces of the pipe.

V = k C R0.63S0.54

New pipes typically start with a very high C coefficient — supporting high flow rates — but that number decreases as the pipe deteriorates. One form of deterioration is tuberculation, which occurs as pitting corrosion products buildup. While some materials like steel can be affected by tuberculation, with its C coefficient decreasing by more than half in about 50 years, HDPE pipes are unaffected (4).

But what happens once the pipe has reached its end of service? How recyclable is HDPE?

AGRU XXL HDPE pipe was used to construct the new 2250 mm OD (SDR 21/26) outfall pipe for Capital Region District’s (Canada) new tertiary wastewater treatment facility.
Recyclability of HDPE pipes
HDPE pipes are relatively easy to recycle compared with other piping materials. One approach is to shave down and reprocess HDPE pipes into pellets to be used later in other industrial applications. This process can be repeated, with experiments showing that HDPE can be recycled multiple times without affecting its properties. And by recycling the material, HDPE pipe’s life cycle assessment is further improved.

Another important point to make is the versatility of HDPE pipes. For example, over the last few decades HDPE pipes have been entering new markets such as gas distribution. Today, many gas lines are being converted to HDPE to help reduce leaks and improve long-term performance.

From landfill liners to highly durable pipes that keep sewage within the system until it can be treated, it should be clear that HDPE has become an essential material in protecting our environment. HDPE as a piping material is beginning to gain traction in the United States, but it is still far from the most popular option. But with time and effort dispelling misconceptions about plastics in general, it is possible that HDPE will become an ideal choice for most future piping solutions.

  1. Infrastructure Report Card.
  2. M. Najafi, A. Habibian, and V. F. Sever, “Durability and Reliability of Large Diameter HDPE Pipe for Water Main Applications.” Water Research Foundation. (2015). Accessed online 23 June 2021.
  3. Lifecycle Assessment of North American Stormwater Pipe Systems.
  4. G. Maingi, “High-Density Polyethylene (HDPE) as a Replacement Material for Carbon Steel Pipes in Geothermal Projects.” KenGen. (2017).
Melissa Grace is the AGRULINE pipes and fittings technical unit manager for AGRU America, Inc. For more information, contact AGRU America, Inc. at 500 Garrison Road, Georgetown, SC 29440-9680 USA; phone (843) 546-0600 or (800) 373-2478, fax (843) 546-0516, or