Carbon and glass fiber reinforced polymers (FRP) have been used for infrastructure for more than three decades, and applications in pipeline and other belowground infrastructure rehabilitation have gained momentum in recent years.
The advantages of these systems include high strength, corrosion resistance, lightweight and the ability to be installed on essentially any type of structure, size and geometry. FRP liners can also be used to increase internal pressure and improve the flexural and buckling capacity of deteriorated or non-deteriorated pipes. FRP liners essentially consist of carbon or glass reinforcing fabric that is saturated with an epoxy resin and then applied using the wet layup process to the prepared surfaces of the host pipe. Carbon fiber–reinforced polymers (CFRPs) are typically used for pressure pipelines. Glass fiber–reinforced polymers (GFRPs) are typically used as the first layer of material to contact any metallic substrate to provide a dielectric barrier between the metallic substrate and the CFRP materials, in addition to added strength to the FRP system.
An FRP system can be installed internally or externally on a pressurized pipe. The upside of external wrapping is that the existing pipe can be renewed without any interruption to the service; the downside is if the pipe is corroding internally, external wrapping will not prevent it from progressing further. If such pipelines are exposed to direct sunlight, an ultraviolet radiation protection coating should be used. For internally lined systems, a corrosion and abrasion resistant top-coat (min 30 mils) is recommended to prevent any hydrogen sulfide-induced corrosion as well as abrasion that could result from sand and other sediments transported particularly in a force main.
Alternatively, an FRP system can be prefabricated as pipe segments and installed with the sliplining method. While installation will be faster, this method may result in significant reduction in the host pipe diameter, and for most cases, will require the annular space between the host pipe and liner be filled with cementitious or polymeric grout. Another downside of sliplining is that it may require excavation of access pits to accommodate installation of the FRP pipe segments. Properly designed and installed FRP liners can completely restore a deteriorated host pipe and reset the service life for another 50 years or more.
The objective of an FRP design is to ensure the FRP liner will remain functional when subjected to service loads over its design life and have the necessary strength, reliability, and durability. The available design references include ACI 440 , AWWA C305 ASME PCC2 /Part 4, and the recent guideline specification published by NASSCO. While some design equations are provided in these standards, guidelines, as well as in technical papers on FRP design, particularly, semi-structural rehabilitation can be complex and may require computational modeling with the finite element method as well as testing for loading conditions on different FRP configurations. Stress concentrations are possible at seams, joints, cracks and other surface irregularities.
Case studies on two force mains and one low pressure sewage process pipe rehabilitation with FRP are discussed briefly below.
84-in. Pump Station Discharge Pipe Renewal
Installation phase of a proprietary FRP composite system into the 84-in. sewage discharge force main. Shown here are the 3D polymeric fabric being installed on top of fiberglass layer (with a tack-coat on top of the fiberglass).
Installation phase of a proprietary FRP composite system into the 84-in. sewage discharge force main. Shown here is the finished product with the top-coat and dual-band compression seals at end terminations.
This project was comprised of fully structural rehabilitation of an 84-in. steel discharge pipe at the North East Sewage Pump Station (NESP) in Detroit, owned and operated by Oakland-Macomb Interceptor Drain Drainage District (OMIDDD). The design factored in an internal pressure of 15 psi and external (hydrostatic) pressure of 17 psi. The low internal pressure could be met with a single layer of carbon fiber laminate. Nevertheless, a dual layer glass fiber and a proprietary 3D polymeric fabric layer was used to serve as a dielectric barrier between steel and carbon fiber, improve impermeability, and achieve the ring stiffness needed for external load. The project was completed as planned with some additional effort to stop leaks by chemical grout injection through the invert of the pipe.
48-in. Pump Station Discharge Pipe Renewal
Structural rehabilitation of a 48-in. sewage discharge force main with a patented FRP composite system. Shown here are 10-ft long prefab pipe segments.
Structural rehabilitation of a 48-in. sewage discharge force main with a patented FRP composite system. Shown here are branch connection sealing upon installation.
A patented prefab FRP system with glass, carbon, and proprietary 3D layers was installed for a fully structural rehabilitation of a 48-in. sewage discharge pipe at the Avalon Pump Station in Los Angeles County, California. The prefab FRP liner was designed to take the external loads (groundwater pressure) and 30 psi of internal pressure. The outside diameter of the FRP liner was 47-in. leaving a 1-in. total annular space. The installation was done with the sliplining method and the annular space was filled with epoxy grout by tubular injection.
30-in. Low-Pressure Pipe Renewal at Water Reclamation Facility
Low pressure iron pipe rehabilitation with GFRP depicted before lining.
Low pressure iron pipe rehabilitation with GFRP: the dual-layer GFRP laminate as installed.
Low pressure iron pipe rehabilitation with GFRP: the finished product with the top-coat.
The third example project is from the Village Creek Water Reclamation Facility in Fort Worth, Texas. A process pipe conveying thickened raw sewage at low pressure was lined with a dual-layer GFRP to prevent corrosion, abrasion, and restore structural capacity. The pipe is in a gallery with limited access, thereby making any large equipment unfeasible for use to install a lining system. The GFRP system was installed with no special equipment and by person-entry. Some patching with quick setting cementitious grout was carried out in addition to the sand blasting the surface prior to installation of the GFRP system. The GFRP liner was finished with a corrosion and abrasion resistant top-coat (epoxy based).