Municipal drainage and sewer systems are essential for maintaining hygiene and minimizing flood hazards, but aging infrastructures mean that keeping these systems in good repair is becoming a growing challenge. To avoid the major expense and disruption involved in replacing large sections of these pipe systems, managers are exploring alternative techniques for extending the life of their assets, especially trenchless rehabilitation methods. Cured in place pipe technologies are the most frequently used of these trenchless methods, and so far seem to have proved the most effective.
Any Kind of Pipe
The cured in place pipe technology, or CIPP, process can be employed to rehabilitate virtually any kind of pipe, including clay, cast iron, concrete or corrugated metal pipes, and any size from 2″ to 96″ in diameter. As well as cylindrical pipes, the process can also be used for other shapes, such as egg-shaped and box culvert pipes. The method was originally intended to be used with gravity pipelines, but more recently, techniques have been developed for pressure pipes as well.
How it is done
The CIPP process starts by cleaning the pipe with a water jet, diverting the flow if necessary, to remove all tree roots, debris and silt deposits, and there needs to be an inspection, usually by remote CCTV, after cleaning, to ensure it has been done thoroughly. Once the pipe is clean, the liner can be inserted. The liner is manufactured to fit the specific pipe, and is made from fiberglass or nonwoven polyester felt.
After manufacture, and before insertion, the liner is impregnated with a resin, which may be polyester or silicate, but nowadays is normally epoxy resin. The impregnation, known as wet-out, may be done at the factory, in which case the liner must be transported to the site in refrigerated trucks, but is now more often done at the site, using a mobile wet-out unit. The resin includes a chemical catalyst to facilitate the curing process.
There are two possible methods of installation — inversion, or winching. With the inversion method, the sewer epoxy lining is turned inside out using air or water pressure, and pushed along the inside of the pipe. Alternatively, the epoxy sewer liner can be winched into place via a manhole, or through a specially prepared access point, and then inflated to fit the host pipe.
The final stage is the curing in place, which is done by the application of heat using hot water, steam, or ultra-violet light, causing the resin to harden. When the cure is complete, the liner is cooled slowly to prevent shrinkage. The ends of the liner are trimmed flush with the pipe ends, and sealed where necessary.
More Pros Than Cons
The cured in place pipe technique offers many advantages over the traditional “dig and replace” method. The very fact that no excavation is required makes it far less time-consuming and far more cost-effective, and more environmentally friendly, since there is no waste to dispose of. Pipes can be repaired underground without damaging any surface materials or structures.
The benefits of CIPP can also be seen in the quality of the pipe repair. The sewer epoxy lining increases the flow capacity, since the inside of the pipe is smoother, and calcification deposits no longer stick. As it is a one-piece liner, it eliminates root infiltration, and it also bridges offset joints and gaps caused by missing pipe sections. The epoxy sewer liner is completely corrosion-proof; meaning the longevity of the pipe is greatly increased.
There are also one or two disadvantages of CIPP, the main one being that the host pipe has to be taken out of service during the installation and cure process. This could be for anything from a few hours to more than a day. The other main drawback is that the sewer epoxy lining follows the alignment of the host pipe, so does not correct any structural defects.
Over the last two or three decades, advancements in cured in place pipe technologies have revolutionized the pipe repair industry. Despite a few drawbacks, CIPP has shown itself to be the most adaptable and versatile of all the trenchless pipe rehabilitation methods. There will always be situations where excavation is the only option, but in a world increasingly crowded and polluted, CIPP has not surprisingly become the number 1 method of pipe repair.