“Old Fashioned Liners”…Hardly

The history of felt liners dates back to 1971 when the first tube was impregnated with polyester resin, wrapped in a plastic sheet, pulled into place, inflated and left to cure in London, England. The 100 year-old brick egg-shaped sewer was tested in 1991, after 20 years in service, and it met the flexural modulus requirements by a margin of more than 20%. Technical guidelines and standards play an important role in the acceptance and growth of technologies, particularly in the municipal infrastructure business. ASTM F-1216 serves to build confidence in the CIPP concept and requires utility owners, contractors, and their suppliers to implement proper systems for product design, acceptance, quality control and assurance.

In 1997, Applied Felts expanded its business from the United Kingdom to the United States of America. They added a manufacturing plant in Martinsville, Va. to service the growing demand of installers of the felt and resin liner system. Today, as the world’s largest manufacturer of felt liners, Applied Felts has ISO 9001:2208 accreditation in every phase of manufacturing – including a 28-stage testing system – all of which is done in one location, ensuring confidence that their liners will stand the test of time. Applied Felts selects the exact polymer granules and felt fibers that best suit each job and manufacture the felt in-house to the exact size and application that specifications require. After testing and inspecting the polymer granules and felt fibers, a number of additional tests are done including density, thickness, fiber distribution evenness, strength and weld-ability of the finished felt and coating. Applied Felts works closely with Tri-State Utilities to assess unique job conditions and project requirements. This teamwork is especially important when manufacturing non-typical or transition liners.

Most importantly, resin systems have evolved. As Kaleel Rahaim, Thermoset Business Manager with Interplastic Corp. states, “We have evolved in that we have manufactured second generation resins and we are working on third generation products where we can tweak the polymers to give better mechanical properties….” The resins we use today are superior to earlier formulations and can be specifically designed for today’s sewers. One of the important properties to consider is the flexural modulus of elasticity. The standard resins that Tri-State Utilities receives from Interplastic Corp. exceed ASTM F-1216 requirements of 250,000 psi. These standard resins offer a flexural modulus of elasticity of 500,000 psi. Enhanced resins now exceed 500,000 psi (without the aid of fiberglass laminates.) Enhanced resins allow for exceptionally higher modulus properties and are more resistant to stress cracking. Using enhanced resins also result in less shrinkage of the liners and cure at a lower temperature.

Laboratory Tested Mechanical Properties
ASTM F-1216 Standard Resins Enhanced Resins
Flexural Modulus, psi 250,000 500,000 628,000
Flexural Strength, psi 4,500 19,500 9,295
Tensile Strength, psi 3,000 10,000 6,205
Curing Method Water or Stream Water or Stream Water or Stream

Installation practices and techniques have continued to evolve over the years as well. Tri-State Utilities became a licensed installer of the CIPP Corporation in 2000, and concentrated their efforts on time-proven water inversion and a hot water curing system. By 2002, Tri-State Utilities had two crews that used an air inversion and steam curing system. For the past decade, steam cure has become the accepted process and is being used more frequently. Steam is the most cost-effective method that requires the least amount of time and labor to initiate an effective cure and is used to cure polyester resins, vinyl ester resins, and GRP (Glass Reinforced Pipe) liners.

The continuing evolution of resins has tremendously expanded the market for CIPP liners and has allowed the product to be more useful in a variety of applications. While the product still looks the same, the mechanical properties of the current generation of CIPP Corp. liners far exceed those of just ten years ago.

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This post was written by Tri-State Utilities

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