|DN 1500 - moving forward with UV
As the demands of the sewer rehabilitation market develop, constant technical development from both the liner and equipment manufacturers is required. One of these developments has been the use of ultra violet light (UV) cured rehabilitation technology. Not many years ago, UV was only used in small diameter pipework by a handful of installation contractors. Over the years UV has become a more accepted rehabilitation technique with greater (year on year) rehabilitated metereages achieved with diameters up to DN1200. Recently the trial of a new large diameter DN1500 liner has been successfully completed in a joint partnership between ProKasro Mechatronik and iMPREG at iMPREG’s test facility in Ammerbuch, Germany.
The UV light source technology used back in 2000 was mostly limited to light bulbs of 400w combined in a light train of 6 bulbs. This would give relatively slow curing of liners up to DN500. Very few contractors and manufacturers would have been in a position to use heavier and bigger light trains to cure liners up to DN1000. As UV curing technologies have developed combined with advancements in liner and resin materials, the number of contractors with the ability and professionalism to install larger diameter liners is increasing rapidly. ProKasro now manufacture UV light trains with 8 x 1000 watt bulbs giving almost four times the power of systems from 10 years ago.
As energy costs continue to rise, water usage becomes ever more critical and social impact due to noise, site footprint, road closures is higher in the priority list of planners, project managers and clients alike, alternative sewer rehabilitation techniques such as UV are being specified and approved. Cost efficiency is critical to the success of any project and as developments in larger diameter liner technologies arrive, cost to the end client is reducing. Combine this with the data logged quality management documentation provided for each and every job site, the end client can be assured that they are getting the best rehabilitation technique at the keenest price.
To obtain suitable strength curves for large diameter liners, thicker liner walls are required. Due to the wall thickness requirements, the concept behind the curing of large diameter glass reinforced plastic (GRP) liners is the use of a combined curing system. The combined curing system is a fusion of traditional exothermic heat curing and modern UV light curing. The curing process is activated by ultra violet light waves as normally used for UV curing. Special peroxides within the liner resin are activated by the UV light at high temperatures and guarantee a fully cured liner. With the new combined curing technique, there is theoretically no limit to designing large diameter liners with thicker walls.
UV light curing of the DN1500 liner at iMPREG’s test facility
As larger diameter GRP liners are developed, handling, user friendliness and installation issues become more evident. Weighing in at 150Kg per metre the installation of a DN1500 liner requires the use of roller beds and motorised transport bands to ensure successful installation. During
installation, stress is also placed on the liner itself. The unique design of the iMPREG liner perfectly handles all axial and pulling forces. The axial orientated, non broken fibre weave pattern of the iMPREG liner performs even better as thicker liner walls are designed. From the installation contractors perspective, support is pre designed into the delivered liner. This ensures that fitting of the pressure end caps is carried out smoothly and efficiently and gives a stronger grip on the liner during liner pressurisation. Without this pre designed support, the pressure end caps would be very difficult and time consuming to install on site.
Then light source used during the test was 8 x 1000 watt bulbs and had to be customised for this new large diameter. Fundamentally the light train was ProKasro’s proven ‘double core’ light train with 2 cores each running 4 x 1000 watt UV bulbs. The inflation pressure is produced by high capacity radial air blowers. These blowers are designed and built into the mainline UV curing vehicles manufactured by ProKasro. These special machines pump air at high volume and low pressure with minimum water content into the liner. The electrically elevating UV light train was placed into the liner after assembling both end caps and after increasing the internal liner pressure by 100mbar, the light source was electrically centralised into the curing position. Pressure was increased in the liner to approximately 250mbar and the light source was then drawn through the inflated liner and (using the light train’s onboard camera) an inspection of the inflated liner prior to curing was made. The light train was then switched on a pulled back through the liner at a computer controlled speed to cure off the liner. All steps were data logged at thirty second intervals including speed of cure, temperature, length and CCTV picture as is common with all UV lining operations. After successful curing, the liner end caps were removed, the liners inner foil removed and samples of the cured liner were taken and tested at iMPREG’s in house laboratory and showed perfect results.
Now the initial trials have been concluded and excellent results have been returned, attention can now turn to improving both the liner itself and the curing equipment. The UV market is developing rapidly and as such the new liner designed by iMPREG combined with the curing equipment manufactured by ProKasro enables contractors to offer further reliable systems to their end clients. This can be borne out by the fact that a recently completed project between ProKasro, iMPREG and one of iMPREG’s contractors successfully installed approximately 500 metres of DN1250 x DN940 egg profile sewer in under two weeks. This included all jetting, CCTV and lateral re-opening.