THURROCK, Essex, UK, March 14, 2008 -- As compared to some widely accepted pipe lining systems available on the market today, the emergence of the latest air inversion/steam cure technology brings with it many advantages.
Unfortunately air is not very good at transmitting heat, however steam is. Steam is also very controllable and allows linings to be heated to over 100°C. The advantage of this is that liner resins cure more quickly when cure temperatures are raised. In practice it is only the inside face of the resin that reaches these higher cure temperatures, the outside of the resin is cooled by contact with the host pipe. So, on steam cured linings, temperatures are held at between 110°C to 120°C and temperature between the liner and host pipe are monitored to insure a more thorough initial cure. Steam cures combine the thoroughness of water cure with the speed of UV cure systems.
In addition to this, Insituform Technologies Ltd (ITL), a widely respected and renowned lining systems manufacturer and contractor, also has the major advantage that it manufactures its own linings in the UK and, as such, is largely independent of the vagaries of the longer (non-domestic) supply chains experienced by some other contractors. This means that ITL's services are very competitive and highly cost-effective, as well as enabling a rapid response with minimum lead times as and when required.
Another key benefit of air inversion with steam curing is that the installation and curing units are separate items. With water inversion and cure based linings it is necessary to keep the tower or CHIP unit in place until the linings have been cured and cooled. However, once a tube has been installed with air, the launcher could be removed, reloaded and redeployed on the next section of pipe at the same time as the first section of pipe is being cured, so adding to the time savings provided by the quicker curing process.
One other benefit that has proved popular with the installation crews is that there is no water circulation hose. Once the lining has cooled and the ends cut off that is it, job done! There is no hose to pull out and no scaffold tower to dismantle and load into a truck.
The steam cure systems also provide for less disruption per job site due to the faster installation and cure times and simply because the work site is there for a much reduced time. The use of steam curing also creates less waste water and odours, greatly reducing customer complaints.
Limitations Overcome
There are some limitations with some of the steam cure systems currently available to the market, not least being that most currently available systems offer lining installations up a maximum of 400 mm diameter due to the system relying on turbulence to heat the lining evenly during curing. ITL, however, has overcome these limitations by recently developing its air inversion/steam cure equipment so that ITL can now install liners up to 1.2 m diameter.
Additionally, linings that are installed with water effectively float through themselves as the inversion proceeds so there is no 'real' limit as to how long a single inversion can be. Air inverted linings are, on the other hand, subjected to more friction and drag during the inversion process. This means that higher pressures need to be used for longer linings. Up to 250 m is thought to be possible per air inversion in small diameter pipes. However, ITL's development of new its inversion system has allowed its engineers to also overcome this limitation to a large extent.
Thurrock Linings
As part of a recent project for Anglian Water Services (AWS), one of the UK's ten major water companies, and part of the Anglian Water Group, ITL undertook a sub contract for pipe relining work using air inversion/steam cure techniques.
The main contractor for the project, known as 'Thurrock Sewer Rehab Solutions', was Barhale Construction plc. Barhale is a member of the @one Alliance, a collaborative organisation established to deliver Anglian Water's AMP4 investment program. The lining works covered several site across the Thurrock area which lies to the east of London, adjacent to the A13 trunk road in Essex.
The aim of the rehabilitation work was to rejuvenate a series of Grade 4 and Grade 5 sewer pipes to a minimum Grade 2 standard.
In order to achieve the aims of the project, whilst minimising the disruption and environmental effects of the rehabilitation operations, ITL, in conjunction with the client and its main contractor, decided to utilise the latest air inversion/steam cure lining technique which recently became part of the ITL solutions portfolio. ITL believed that the steam cure option would provide faster installation times and therefore less disruption to everyday life in the heavily populated residential areas in which the work was to take place, whilst offering a technique that minimised styrene odour issues, which can be associated with other inversion renovation techniques. Other options were considered but ultimately the environmental aspects, time factor and cost of installation proved the steam cure technique to be the most 'cost effect' from all view points.
In total some 192 individual lining operations were undertaken over a timescale that started in March 2007. In all the actual lining works were completed in just 12 weeks.
The linings required were for pipes of diameters including 150 mm, 225 mm and 375 mm. None of the installations has yet exceeded 200 m in length and none of the pipes exhibited deformations of greater than 10%, with many showing less deformation.
Prior to the liner installations all pipes were cleaned and CCTV surveyed to ensure their suitability for the lining technique and topographical surveys were made of each installation site.
Typically a lining operation would comprise the utilisation of a Snail Inversion, a compressed air driven unit to invert an average liner length of around 100 m into the host pipe, although it is possible to install liners up to 200 m in length in 150 mm diameter pipes using this technique. The liner product used throughout was ITL's own CIPP liner tube. The time scale from the start of the inversion to the completion of the steam cure was typically 5 to 6 hours. The unit used to cure the liner was a standard Steam Generator producing up to 1,200 kgm/hour of steam.
Despite the number of installations, the locations and the potential for disruption, no problems were encountered throughout any of the lining operations. Not only that, but at times during the work schedule, ITL achieved what it believes to be a record installation meterage in its time on site, mainly because the faster steam cure option enabled the workforce not only to save time per installation but also to limit the footprint of the site which, in turn, meant the need for only limited use of traffic control measures. So the team's time presence at any one site was kept to an absolute minimum.
As well as ensuring the sites themselves were operated to a minimum timescale, ITL also took part in a major public relations operation to ensure that all local residents and businesses understood what was to take place, as well as where and when, to ensure that necessary alternate routes for traffic flow were used to best effect. This part of the project involved leaflet distribution and the publication of road traffic notices.
Commenting on the work for Barhale, the @one Alliance's main contractor on site, Richard Beecroft, Barhale's contract manager, said: "The works went very smoothly. ITL's ability to complete two lines in a day resulted in rapid production and minimised disruption in an urban environment. The use of steam cure significantly reduces issues with styrene odour, which is often a cause of complaint from members of the public with traditional water cure operations."
John Beech, ITL's business development manager, said: "The air inversion/steam cure lining option is one of the latest additions to the broad family of pipeline renovation options ITL now offers. Whilst our traditional water inversion/hot water cure system still offers an ideal solution in many circumstances, interaction with the public and local businesses has become a major issue in recent years. We have therefore expanded our portfolio of renovation solutions to include a variety options which allow us to minimise the way we affect the operational location so as not to impinge significantly on the local environment or its population. Whilst others have opted for systems such as UV cure linings we believe that our air inversion/steam cure option often offers a more overall cost effective solution, not just financially but in time terms as well."
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