Jon Briafield at PE pipe specialist, GPS PE pipe Systems, advises on the considerations for pipe specification and the types of pipe required for different elements of a water installation.
Regardless of the water pressure, geography of a site or its previous use, polyethylene (PE) pipe is the ideal solution for residential water infrastructure projects. Durable, flexible and abrasion resistant, it has a service life of at least 100 years and is suitable for installation by either open cut or trenchless methods. However, this does not mean that PE pipe is a one-size-fits-all solution; far from it. The right type and size of pipe must be specified for the installation and there are numerous considerations and calculations that come into play.
The required flow rate and the minimum and maximum water pressure should be considered when determining the size of pipe required.
The size of pipe used will also affect the price, as larger diameter or thicker walled pipes require more raw materials which increases the cost of manufacture.
As a general guide, where water pressure is low, a larger diameter pipe will be required to maximise flow rates but the low pressure will normally allow a thinner pipe wall. This is usually expressed as an SDR (Standard Dimension Ratio) and where the SDR is lower the pipe wall is thin relative to the pipe diameter. Where the water pressure is high, a smaller pipe diameter will be sufficient for the required flow rate but the pipe wall will need to be thicker to withstand the water pressure, which will lead to a higher SDR rating.
Coping with contaminants
Where there is no risk of development land being contaminated, a standard PE 100 pipe will provide the ideal solution for the main drinking water feed and the pipe supplier should be able to provide technical support with specification of the right SDR for optimum flow rate and service life.
If there is any risk of contamination, it is important to establish whether the chosen pipe will provide a sufficiently robust barrier. However, soil sampling can be very expensive and often the most cost effective approach is to specify a PE barrier pipe that provides a proven impermeable barrier against all recognised organic and inorganic contaminants, even in their maximum reported concentrations. In this way, identification of the type and level of contaminants is no longer required reducing the potential for delays on the project and cost implications that soil sampling may incur. Specifiers should look for a proven barrier pipe system that is kitemarked to WIS 4-32-19, the Water Industry Specification standard for barrier pipe systems determined by Water UK, the representative body of the UK water and wastewater service suppliers.
The eco-friendly challenge
As we get ever closer to the deadline for zero carbon homes, the challenges of incorporating eco-specification into deliverable and sustain-able projects increase. In terms of water infrastructure, water re-use and rainwater harvesting are key elements of the drive towards environmentally responsible specification but with these innovations come new specification and installation challenges.
Developers must ensure that there is no risk that a rainwater or grey water supply can be confused with a drinking water supply on the pipe network, either during the build programme or during maintenance at a later date. To be certain of this, a PE pipe designed specifically for re-usable water supplies should be specified and the Water Regulations Advisory Scheme (WRAS) and the National Joint Utilities Group (NJUG) recommend a black PE pipe with a green horizontal stripe at each quadrant. As with all types of PE pipe, specifiers should expect their supplier to offer a wide range of sizes and fittings to ensure an easy to install and maintain, leak-free solution.
For wastewater and sewage pipes, specifiers should select a black PE 100 pipe in an appropriate size to cope with the required demand. Once again, it’s important to select a pipe system with a wide range of fittings that can help to underpin length of service life not only of the pipe itself but of the complete installation.
Whatever the specific water infrastructure considerations on an individual site, it pays to understand the different integrity and colour-coding requirements of the varied aspects of an installation. However, it’s important to remember that the pipe supplier is the expert and, whether the pipe materials are bought direct from the manufacturer or from a merchant, tapping into that expertise by accessing the manufacturer’s technical support team can help to ensure the most durable, easy to install and cost effective specification.