There are approximately 2.4 million miles of water pipe in the United States. The average life expectancy of these pipelines is 80 years. The average age of failing water mains is 54 years, and 33% of all mains are over 50 years old. Open cut pipe installation is the most common method of pipe replacement used by 93% of utilities. Trenchless pipe relining is used by only 32% of water utility entities.
There are two main options for pipelining without excavation: cured-in-place pipe (CIPP) and flexible fabric reinforced plastic pipe (FFRPP). CIPP is a well-established trenchless technology for pipe rehabilitation, but it faces some technical, structural and logistical limitations when applied to pressurized pipelines. Compared to FFRPP systems, CIPP often presents higher risk and greater field complexity, particularly in high-pressure and long-distance applications. FFRPP trenchless rehabilitation for pressurized water, wastewater and industrial pipelines can provide benefits such as shorter downtimes, reduced environmental disruption and less economic impact on businesses and communities. These factors can significantly influence overall cost-effectiveness.
CIPP is a trenchless rehabilitation method used to repair existing pipelines and was developed in the early 1970s. It is a jointless, seamless pipelining within an existing pipe. The process of CIPP involves inserting and running a felt or fiberglass reinforced lining into a preexisting pipe that is the subject of repair. Resin within the liner is then exposed to a curing element to harden it and make it attach to the inner walls of the pipe. Once fully cured, the lining acts as a new pipeline.
FFRPP liners have a history dating back to the early 2000s. The initial focus and development of these types of lining systems was on the offshore gas and oil side of the industry. FFRPP liners are factory manufactured round pipe that is flattened, folded and then coiled onto reels. Two types of FFRPP liners, close-fit and loose-fit, are used in the U.S. Both share common traits in material properties and installation methods and yet vary significantly in how they are manufactured and operated.
These FFRPP options are well-suited for pressure pipe rehabilitation applications. Their structure includes a modified abrasion-resistant polyethylene (PE) outer layer, a middle layer of fabric reinforcement (options include seamless woven polyester, aramid or a combination) and a modified PE inner layer that allows folding and rerounding during installation.
The primary differences between close-fit and loose-fit FFRPP liners lie in their manufacturing process, available diameters, fit once inside the host pipe and termination fittings. Loose-fit liners are manufactured using coextrusion and do not fit snugly against the host pipe's inside diameter but rather leave a large annulus between the host pipe and new liner. The maximum size available for this type is currently 20-inch nominal, resulting in a final finished inside diameter of approximately 17.2 inches. The annular space created by loose-fit designs can accumulate corrosion, soil infiltration, impurities and contaminants within the pipeline and can affect the longevity or overall design life.
Close-fit designs extrude the jacket and liner partially through woven fabric layers, resulting in greater tensile strength and adhesion. This allows for manufacturing and installation of sizes up to 64 inches. The close-fit design eliminates annular space, provides a smoother roughness coefficient for increased flow capacity and offers a sustainable 50-year service life to failing pipelines. Moreover, the close-fit design meets the criteria for an American Water Works Association (AWWA) Class III semi-structural liner, offering a close fit design, a self-supporting rigid structure and the ability to bridge holes and gaps in the original host pipe.
There are several differences between CIPP and FFRPP systems. CIPP liners must be installed completely smooth and wrinkle-free to maintain structural integrity and pressure capacity. Any wrinkling during installation can lead to stress concentrations, compromised pressure resistance and premature liner failure. This level of quality must be achieved entirely in the field. Once wetted out, CIPP liners are heavy and lack inherent structural support until cured. These characteristics limit pull-in distances to less than 500 feet in many cases, necessitating frequent access pits and increasing cost. To avoid wrinkling and ensure proper fit, CIPP installations in pressure systems typically require preinstallation laser profiling. This process involves depressurizing the pipeline, excavating at 1,000-foot intervals, dewatering and cleaning before performing the laser scan. This can be a high-cost, time-intensive process, but it is essential to reduce installation risks and ensure proper liner performance.
CIPP systems cannot conform to bends or significant deflections in the host pipe due to the requirement for a wrinkle-free finish. Even minor misalignments or directional changes identified during laser scanning must be excavated, removed and replaced and often require custom fittings or structural work. This adds significant time, cost and complexity to the installation. CIPP liners are often pressure-limited, especially when field-installed without optimal curing or fit. Specific limitations include reduced pressure capacity in wrinkled or uneven sections, limited ability to withstand higher or sustained internal pressures and occasional need to reduce or waive standard pressure testing criteria due to performance uncertainty.
CIPP requires an intensive multi-step installation process, including resin wet-out (often on-site), pull-in inversion into the host pipe, controlled inflation, curing, cooling and trimming. This process is labor- and equipment-intensive with increased field variability.
CIPP lacks standardized mechanical end fittings. To complete the system, internal and external seals must be installed on-site, and custom transitions are required to connect to the host pipe so the internal couplings have a new pipe interior to seal against to try and ensure a leak-free fit.
These termination procedures are time-consuming and increase the potential for long-term leakage. While CIPP remains a useful technology in specific applications, its use in pressure pipeline rehabilitation is constrained by:
- Strict installation geometry and wrinkle-free requirements
- Inability to navigate bends or deflections
- Short pull-in distances and heavy liner profile
- Labor-intensive preparation, curing and installation
- Complex, nonstandard termination requirements
- Limited and uncertain pressure test performance
In addition to the inherent differences between CIPP and FFRPP systems in regards to materials, composition and installation methods, there are also distinct benefits to FFRPP from a manufacturing perspective. FFRPP liners are factory finished, and the quality assurance and quality control on the finished product are all performed at the factory. FFRPP can be installed over several thousand feet, reducing installation time and minimizing site disturbance. It can flexibly navigate bends and deflections due to its factory-finished design and mechanical properties, avoiding unnecessary excavations and accelerating project timelines. The system is pretested and certified for pressure applications, significantly reducing the risk of pressure testing failure. The installation is faster, as it arrives ready to be pulled into place, requires no curing and involves minimal post-installation work. The close-fit liner includes engineered mechanical terminations, ensuring a quick, secure and consistent connection at each end.
Factory-finished systems offer:
- Long-distance pull capability
- Flexibility through bends
- Pretested pressure ratings
- Rapid installation
- Reliable mechanical terminations
As a result, factory-finished FFRPP systems can provide a fast, reliable and cost-effective solution for pressure pipe rehabilitation.
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