Plastic Pipes: Number One Choice for Water & Sewerage Applications
30 April 2010
Since their introduction 50 years ago, plastics have become the pipeline materials of choice for today’s water industry, rapidly taking over the ductile iron and other traditional options. In this article, we look into the reasons of this success.
Plastic pipes for potable water and sewage applications have been in use in the UK since the 1960’s. Since that time, production techniques and applications have evolved, but essentially plastics have repeatedly shown that they are the superior materials for a great range of installations, and now set the standards that others must follow.
Many practical and cost benefits of plastics derive from their inherent properties. Firstly, plastic pipes made from polyethylene (PE) and polypropylene (PP) materials have the flexibility to tolerate ground movement without cracking, whilst at the same time being sufficiently strong to prevent excessive deformation under the combined effects of backfill and traffic loading.
Plastics also address one of the key concerns for the water and sewage industries: leakage. There is a cost associated with the acquisition, treatment and supply (pumping) of water, and if a water distribution system leaks, the lost water can become an extremely high cost. Plastic pipes have an advantage in leak resistance over other materials. This is because they need fewer joints, as they can be produced, transported and installed in longer lengths. Typically, clay and concrete pipes have 2 or 3 times the number of joints of plastic pipelines. Furthermore, the butt or electro-fusion processes used to join PE pipes provide stronger, tighter, more leak proof joints. These welded joints are self-restraining and costly thrust restraints or thrust blocks are not required.
The exceptionally smooth and non-porous bore of plastic pipes gives more flow per metre head/mm bore, when compared to ductile iron pipe. Superb corrosion and chemical resistance is another advantage shared by plastic pipes over traditional pipes. In sewer pipes corrosion can occur because of chemical reactions caused by the biological production of sulphuric acid. Plastics pipe will not corrode, tuberculate or support biological growth. They also offer a high level of chemical resistance to a wide range of substances found in both effluent and contaminated soils, making them the materials of choice in harsh chemical environments. Freedom from corrosion ensures that hydraulic characteristics are superb and will remain so, minimising water losses and pumping costs over the lifetime of the system.
From the construction point of view, plastic pipelines present greater logistical, installation and cost advantages. Light in weight, they allow greater logistical efficiencies and easier on-site handling. PE, for example, is about one-eighth the density of steel, so it does not require the use of heavy lifting equipment for installation. The combination of flexibility and leak free joints allow for unique and cost effective types of installation methods that the rigid ductile iron pipes cannot use. These alternate installation methods (no-dig for example) can save considerable time and money in most water applications. Narrower trenches also lead to lower installation costs as the cost of the reinstatement of the road surface is expensive.
All the major advantages of plastics, combined with a potential for long system life (100 year or more) and reduced maintenance costs, lead to further cost advantages over the long term. The Whole Life Costing Model developed by Thames Water, Borealis, GPS PE Pipe Systems and TRL in 1996 proved that plastic pipes based on PE and PP materials should provide the most economical long-term. The WLC model calculated all costs associated with a pipeline throughout its life cycle, from material costs to installation and maintenance. Even using the most conservative estimates, it found that for larger pipelines, using a PE pipe system can reduce overall installed costs by as much as 70% and whole life costs by 45%.
Importantly, many plastic pipes have better sustainability credentials comparing with traditional materials that were not generally designed with the environment in mind. On top of the advantage of leakage reduction, plastic pipes require less energy in production than alternative materials. According to the PE100+ Association, PE pipe has ten times less environmental impact than the equivalent ductile pipe. This is based on full life cycle analysis, which takes into account not only energy consumption, but also other factors such as effects from emissions.
At the end of their useful life plastic pipes can be easily recycled and because plastic pipes are lightweight, they require less energy for transportation, handling and installation. Finally, PE pipes are the number one choice for trenchless installations, which reduce the need for restoration and roadway reconstruction and allow work under river and lakes with less disruption to the environment.
With the current pressure on water companies to ensure that pipeline installations are not only reliable and cost-effective, but also have a minimal environmental impact, it is no doubt that the growing acceptance of plastic pipes will continue. They meet the requirements set down by today’s water industry and their in-built qualities make them the best materials to adapt to the industry’s needs.