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According to PUBLIC WORKS' exclusive reader survey, cured-in-place piping (CIPP) is the most popular trenchless technology method.
Commonly used to repair cracks, offset joints, protruding taps, and structurally deficient segments, CIPP is installed by using the manhole as an access point and inserting a flexible, fabric liner coated with thermosetting resin into the existing pipe. The resin is resistant to damage from waste-water and consists of unsaturated polyester, vinyl ester, or epoxy.
Once the material is in place, hot water or steam is circulated through the tube to initiate curing and bonding of the resin to the wall of the existing pipe. After curing is complete, TV inspection equipment is then used to locate dimples—which indicate a sewer lateral—in the new lining. Robotic cutting devices are sent into the pipe to cut the lining blocking each service. In large-diameter pipes, the lining at services may be cut manually.
Depending on the installation method used to place the liner, pipe diameters of 4 to 180 inches and lengths of 500 to 3000 feet can be rehabilitated with CIPP. Liner products, such as National Liner—manufactured by Houston-based National Enviro-Tech Group—can range in thickness from 4.5 to 33.5 mm for pipes diameters of 6 to 120 inches. The company's Web site, www.nationalliner.com, offers several tools, such as an engineering design calculator, to aid in CIPP project design.
Sliplining—placing a new pipe into damaged pipe—is the oldest rehabilitation method. The replacement pipe's diameter must be smaller and the resulting annular space must be grouted. The EPA recommends the grout be placed for the entire length of the pipe instead of only at the ends to prevent failures and leaks.
Sliplining can be placed continuously through the existing pipe or in specific segments exhibiting failure for pipe diameters of 4 to 158 inches depending on the application method. Maximum installation lengths can reach up to 1000 feet.
Pipe-bursting shatters the existing pipe with a bursting tool and forces the pipe fragments outward into the adjacent soil. A new pipe is guided into place directly behind the bursting head into the resulting void.
Because pipe-bursting can cause movement in the surrounding ground, the locations of structures and other utilities nearby will determine if this is a viable solution for a project. Used for pipe diameters of 4 to 24 inches, pipe bursting can be installed in maximum lengths of 750 feet.