Applying standards to barrier systems
A rise in brownfield developments has increased the use of barrier piping. Even with the right pipes, however, contamination is still a risk from poor installation, says Richard Graty of GPS PE Pipe Systems
It is no longer necessary to specify metal pipe and fittings with tape wrapping for external protection, as plastic barrier pipes are now predominant in contaminated land applications, particularly in smaller diameters. Manufacturers have introduced purpose-designed plastic pipes and fittings with an integral barrier component.
Indeed, some also offer complete PE pipe systems that are fully approved by the water industry for use in contaminated land. Unfortunately, the increasing choice of product options has shadowed the widening adoption of barrier systems, as the components of such systems are rarely fully interchangeable. This has created a serious pitfall for unwary installers if they take a 'mix and match' approach to pipe and fittings, and can ultimately threaten water quality. Although manufacturers size their pipes and fittings according to industry norms, pipe systems are not standardised, so it is inadvisable to expect that a fitting from 'Manufacturer A' can be used with any success on pipe produced by 'Manufacturer B' unless the combination is specified in the product information.
The Water Industry Standard relating to polyethylene barrier pipe systems for potable water in contaminated land is WIS 4-32-19. This defines performance characteristics and specifies contaminant protection limits for the pressure pipe and compatible fittings. Unless a specific combination of pipes and fittings has been tested successfully, it can never be approved to WIS 4-32-19 and may not be
suitable, indeed even fit for purpose.
The standard was introduced in 2008 and perhaps it is no surprise that any confusion regarding WIS 4-32-19, where it exists in the industry, still needs to be clarified. In a recent paper, one pipe manufacturer asserted that: "To be effective and meet the new UK standard it is desirable to use metal fittings, as plastic fittings do not provide the barrier properties for the total system, and thus such systems fail to meet the requirements of the standard". This is incorrect, as systems incorporating plastic fittings can and do meet the standard requirements. For instance Protecta-Line - one of the first PE barrier pipe systems introduced in the UK - was among the first to receive formal approval to WIS 4-32-19 by obtaining a BSI Kitemark for the whole system.
Crucially, the emphasis in gaining approval lies with the system, not the individual component parts. Moreover, for a system to achieve approval to WIS 4-32-19, each variation must pass the appropriate testing. This means that each pipe size must complete a suite of tests with the various jointing methods authorised by the manufacturer, and with attached fittings and valves in all permutations.
There are exceptions allowing products from different manufacturers to be connected, but only if that combination is tested and approved. The WIS' standard includes the note: "Fittings and joints manufactured by others for use with one or more pipe manufacturer's barrier pipe system, but not tested by the pipe manufacturer, shall demonstrate dimensional compatibility with that system and include full details of all tests carried out, including permeation tests, in the Technical Data File for that product."
Clearly the fittings and joints must be tested and approved in combination. When alternative fittings have not been approved for use in this way, the consequences can be disastrous. Water companies and contractors need to be aware that there is a clear risk of practical difficulties and delays during installation. Not only will the installation be affected, but the performance of the installed pipes and fittings will also be in question. Additionally, the result will certainly not be WIS 4-32-19 approved, even if the core system carries the BSI Kitemark.
Of course, it should be permissible to use different pipe systems on the same site, but it is vital to terminate each system correctly before it connects to another. The correct way to do this is to terminate each system with the fitting tested and approved for this particular system.
In view of possible health risks, individual water companies are averse to allowing any contact between drinking water and aluminium, so it is important to use approved fittings that prevent such contact. Some fittings currently being sold as 'approved' do not afford this protection.
The demand for barrier pipes will continue to grow and their use will become more familiar to contractors and water companies alike. According to figures published last year by the National Land Use Database, the total area of previously developed land in England alone is at least 62,000 hectares.
At some stage, the majority will be redeveloped to provide housing, with an extensive requirement for buried water supply lines. A significant proportion of these supply lines will be installed in PE barrier pipe, as it offers the same benefits as normal polyethylene pipe systems in terms of ease and speed of
installation, longevity and sustainability.
With the potential for water contamination at stake, it is crucial that such barrier systems are not compromised by the use of unauthorised, alternative fittings. Care must be taken to check whether or not alternative components are approved by the system manufacturer, or to work entirely within an established, WIS 4-32-19 approved PE barrier pipe system.