In 1972, Eric Wood had a leaky pipe under his garage in England. He developed a method of in situ renovation that eliminated the need to dig up his garage floor to repair the pipe. Today this is a successful method, used worldwide, to fix deteriorated pipes with minimum disruption to the environment and minimal social impact. In the future, the cured-in-place pipe (CIPP) process will continue to evolve to meet the needs of changing regulatory constraints, provide better installation economics, and use newly developed equipment and raw materials for broader applications.

Evolving technology

Today the CIPP process in North America involves the use of a thermoset resin, a bag generally composed of felt and an initiator system requiring heat or ultraviolet (UV) light for activation. Over 95 per cent of the CIPP liners installed in North America today require heat to activate the system. A relatively new entry to the market in North America is the system cured with UV light. In Europe, the UV-cured system has a much larger market share. The thermoset polymers used are mostly polyester or vinyl-ester resins. These resins are generally styrene-based systems. This holds true for CIPP polymers used around the world. Epoxy resins are also used to a much smaller extent in gravity applications and are 100 per cent solids.

Currently the CIPP process finds application primarily in gravity lines, including sanitary sewers, stormwater lines, and process lines. Current CIPP technology also finds application in low pressure lines such as force mains and low pressure process lines. There is a growing trend to develop products and processes to use the CIPP process in higher pressure lines. These new processes and products are even now becoming available to the marketplace.

Resins

Recent developments in new thermosetting resins include resins capable of handling higher temperatures, more corrosive environments, and higher pressure applications. Some products continue to be styrene-based, others have no styrene and some even have no HAP (hazardous air pollutants) and no VOC (volatile organic compounds). Some resins are considerably more expensive than their contemporary counterparts, some more economical.

In North America, resin producers have introduced lower cost resin systems utilising different polymer bases, as well as alternative enhancing agents. The performance of these systems appears to offer the same benefits as the traditional polymer systems. Resin manufacturers are also beginning to offer resins systems that contain no styrene. The contractor and owner should exercise care in evaluating some of these alternative systems. Some replacements for styrene offer no benefit in the way of resin odour reduction or potential contamination concerns. These systems may claim to be ‘styrene free’ but lead the user down a false path of hope. There are systems that are ‘styrene free’ that do offer a true ‘low odour’ system containing nothing of concern from a human health or environmental pollution standpoint. Resin producers are also beginning to offer resin system alternatives to epoxies, for use in drinking water applications. As more of these systems become available, contractors will begin to develop processes that will offer the owner more alternatives for water pipeline renovation.

Bag materials

Bag materials also continue to evolve. Traditionally, bag construction was all polyester felt and served only as a carrier for the thermoset resins. The resins were the sole contributor to the mechanical properties of the system. Today bags continue to be available with needled polyester felt, but hybrid bags are making a much larger appearance in the marketplace. These bags have various layers including the traditional polyester felt, but also include a layer of reinforcing material in some configuration. These reinforcing materials may be fibreglass, aramid fibres, or carbon fibres. There are also braided products available. Some bag manufacturers are also offering bags made strictly of a reinforcing media.

Much of this technology is being imported from Europe where this type of substrate has been in use for some time. These new configurations allow much broader latitude for the contractor and engineer to design a CIPP liner with a much wider range of application. With these new constructions, the bag now becomes a significant contributor to the mechanical properties of the system. With this change in the mechanical property as a contributing factor for the liner, more challenges emanate in design and testing for CIPP liners.

Curing

There are also new developments in processing the system. As the CIPP process has matured, new equipment has become available for making the process more accurate, faster and more dependable. Hot air cure systems allow a smaller footprint on the project site. This process also promises a faster and possibly more economical project cost for CIPP projects. Hot air CIPP projects also emit less process water to the environment or to the treatment plant.

Other developments include the use of UV light to initiate the polymerisation reaction of a liner. This process is a more mature process in Europe, but still a relatively new one in North America. Using this process promises more and better quality control for the process. New developments in the bulbs for the light train, and bag and film developments are allowing thinner, stronger bags that maximise flow capacities.

A process proven for performance

The evolution does not end here. The future of this process promises new developments to improve both the product properties and economics of installation. One promising area for the future is tying the service connections into the main line. This connection has traditionally been a large source of infiltration into the main line. Even after relining and grouting the connection, inflow reduction was still lacking. New processes are being announced monthly for providing a better ‘seal’ between the lateral and the main line.

As new bag composites evolve, experience, along with the same computer technology used to design composites for marine and bridge applications, may be used to design better bags for the CIPP process.

With the new bag systems and the new thermoset resins available, and with new processing equipment and technology, the contractor and owner will have more options available for pipe renovation using the CIPP process. A process proven for performance will become even better.