Cured in Place Pipe (CIPP) has successfully been used in pipeline rehabilitation for 35 years. The first instance was in London, in 1971 using the Insituform technology. This technology is based on a liner product made out of polyester felt as a resin carrier and polyester resin as matrix. In the first attempt, the liner was winched in place and left under internal pressure to cure.

Since then a number of systems have been developed throughout the world. The term CIPP is used to describe a specific cured-in-place pipe of a particular design, produced from a liner of specified materials, with a wall structure which is uniquely defined for each diameter and wall thickness combination, and which is impregnated with a specific resin system and installed by a specific process.

The liner is then winched or inverted into the host pipe and held under pressure against the host pipe by compressed air, steam or water until it is cured. The liner is then cured by ambient temperature, hot water, steam or ultra violet light, thus forming a structurally composite lining.

For CIPP systems, the distinction between the fibre material used, synthetic fibres on one side and reinforcing fibres is important. For example, if it is made out of glass, in accordance with the European Standard EN13566-4:2002, it has the status of a DIN Standard.

Synthetic fibres like polyester felts are defined as a ‘carrier material’ (described in the above mentioned standard as a porous component of the liner carrying the liquid resin system during insertion into the pipe being renovated) and forms part of the installed lining system once the resin has been cured.

Glass-fibre liners are defined as ‘reinforcement’ and have fibres incorporated in the liner, enhancing the dimensional stability of the liner and the structural properties of the cured composite. Further, the reinforcement may be incorporated in the carrier material, or be a separate layer.

The rehabilitation of small diameter underground pipes is an area where the cost competitiveness of Trenchless Technology is well recognised. Many utility pipelines become defective due to the corrosiveness of modern effluents and they also suffer from overloading and loss of capacity. One of the big advantages of using a reinforced lining material is that the cross area reduction is comparably small.

The CIPP system where curing is initiated by exposure to light has been in commercial use since the mid 1980s. Sweden’s Inpipe AB made their first commercial installation in 1985, a DN 150 light cured liner of 49 m under a car park in the small village Vilhelmina, in Sweden’s north.

Curing a liner by exposure to light of a specific wave length has a number of advantages:

* Pre-impregnation under closely controlled factory conditions with a comparatively long storage time - up to six months without quality reduction; * Liner with excellent stretching performance; * Easy handling - the liners are pre-packed, sealed and crated after manufacture ready for use; * Fast curing, * Environmentally friendly curing process, * Controlled degree of cross linking of the polymer matrix, * High strength; and, * Minimal disturbance to the environment.

UV-light cured CIPP systems

Today, several CIPP systems on the market are using a UV-light cross linked polyester or vinylester resin. Usually they are combined with glass fibre for reinforcement. Curing a liner by exposure to light of a specific wavelength has a number of advantages:

* High structural strength and durability; * Thin wall, reducing loss of capacity, particularly important in small diameter host pipes; * Fast installation, particularly important when working within the limited installation windows that are often imposed by authorities, especially in extreme cases such as highway authorities or airport operators; * Improved quality control - impregnation of liner by the supplier under closely controlled factory conditions including QC tests and test installation of the manufactured liner before shipment to the construction site, guaranteeing a uniformly high quality of the liner; * Minimal disturbance to the environment, with no waste products (such as process water) from the curing cycle; and, * Easy handling - the liners are ready for installation when dispatched from the production plant, without the need for impregnation in a local factory or on site.

The quick and controlled installation process is of great importance in today’s congested streets and working environment.

Every application of light cured GRP in the rehabilitation or treatment of pipes has its unique conditions and requirements. Properly applied CIPP and SPS systems are an effective form of pipeline rehabilitation. For gravity pipes, the use of glass fibre in the cured in place liner reduces the thickness of the liner and facilitates rapid curing through photo-initiated methods. This product improves liner quality, productivity and process control at competitive cost and is well established with more than 20 years of field experience throughout the world. By using a light cured resin with reinforcement, the consumption of energy and raw material used is also reduced – ultimately minimising CO2 emissions.

When considering all the factors influencing the selection of the best suited lining system for a specific project, it is clear that no single method will ever cover all situations, however the UV light cured system offers, in many instances, a very good engineering solution.

References

1. CEN, 2002, Standard EN 13566-4, Lining with Cured-in-place Pipes 2. An Environmentally Sound Technology for the Installation, Maintenance and Repair of Underground Utility Services, UNEP-DTIE-IETC 3. Environmental Protection Effect in Gas Construction by Reducing the Amount of and Recycling Excavated soil.