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Simply put, Unisert’s IT3 multiwall pipe consists of plastic pipe installed within steel or other hard case pipe with a cement-based grout squeezed between the two layers of pipe. This method of manufacturing allows the resulting plastic-lined product to be applied to multiple piping applications where reducing, negating or eliminating the effects of internal corrosion is the primary objective. IT3 is the trade name attached to the multiwall piping approach first developed by Unisert and patented over thirty years ago. IT3 means "Internal Tube 3-Phase" and refers to the tertiary materials concept employed by Unisert in the manufacture and installation of the IT3 multiwall piping system.

plastic lined steel pipeThe basis of the design is that the plastic carrier pipe is separated from the steel containment pipe. This feature allows (1) installation without flanges, (2) limitation of the liner stress state within the elastic deformation range, and (3) use of any plastic pipe as the liner. In terms of the plastic liner, this design is classified as a compressed liner concept since the plastic-steel connection is not achieved through deformation of the polymer component.

The neat cement grout-its design and mix-is unique to the IT3 system. Cement squeezed into the annulus between the liner and the outer pipe combines the two conduits into one multiwall pipe that meets or exceeds double-wall containment requirements, transmits hoop strength, forms a secondary corrosion defense, provides a negative buoyancy and serves as a thermal insulator. Technical Information for detailed information about the design and engineering aspects of the IT3 systems.

IT3 multiwall pipe can be plant manufactured in double random lengths or installed in-situ using the existing pipeline as the outer case. IT3 New Piping Systems feature a unique patented coupling device called the SK Collar that allows for the simultaneous joining of the steel and fiberglass. This welded connection is described in detail under New Piping Systems. For more information on In-situ Rejuvenation the multiwall piping process that Unisert originated for bringing existing pipelines back to optimal performance and operating standards.

Flexibility is the most important word to remember when evaluating the IT3 system. Multiple advantages can be realized with the IT3 system, which has been installed to address external as well as internal corrosion problems, plus chemical erosion and deterioration. The choice of plastic liners is limitless: fiberglass, PE, PVC, PB and other plastics, including some the newer and more exotic high temperature and acid handling plastics, can be utilized. The system can be installed in steel, reinforced concrete cylinder, vitrified clay and concrete pipe, all depending on the design and operating parameters of a given project.

The IT3 system is a logical and affordable choice when all contributing factors are weighed. In-situ installations generally cost 60% of replacement. Additional savings and benefits can be realized in rejuvenating existing pipelines where access is limited or restricted due to right-of-way and other location issues, and in high density and environmentally sensitive areas where periodic replacement and repair cannot be tolerated. The economics are also particularly favorable in submarine pipelines where the internal grout weight can be effectively utilized for negative buoyancy. With the IT3 system, the end result is the achievement of design objectives for superior performance, reduced maintenance, enhanced longevity and additional environmental protection factors.


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