November 2022 Vol. 77 No. 11


Close-Fit Liner: Technical Guide to Variations of Close-Fit Liners for Mainline Pipe

Cured-in-Place Pipe (CIPP) Heat Cured 

(UC) — CIPP is a thermoset resin system (polyester, vinyl ester, felt/fiberglass hybrid or epoxy) that is installed into the existing pipeline to be rehabilitated, with either a felt or fiberglass tube of the approximate thickness designed for the application.

The resin-saturated tube is installed either by directly inverting the tube into position using water or air pressure, or by pulling the resin-saturated tube into place and inflating it. Once in place and properly inflated, the resin system is cured using heat (hot water or steam). Recent technology developments include tubes that are reinforced with various high-tensile fibers capable of increasing the overall strength of the finished CIPP. 

Because CIPP does not bond to the host pipe in sewers, groundwater may track between the CIPP and the host pipe. Supplemental technologies that provide a watertight seal between the host pipe and the new CIPP should be employed wherever groundwater infiltration may enter the collection system, such as at laterals and manholes. Seals have been developed with hydrophilic properties that enable them to be installed in conjunction with the CIPP product. 

CIPP is available in sizes ranging from 2 through 120-inches. It is most cost effective in sizes 8 through 48 inches, though it is routinely used for larger diameters, due to a project’s site-specific parameters. 

The resin-saturated tube can be installed in a variety of common shapes for sewer lines; round, egg, arch, and elliptical. Square or rectangular pipes can be lined but can provide many challenges to fitting the CIPP tightly. Multiple bends up to 90 degrees and transitions in size and shape have been accomplished successfully by fabricating the tube accordingly. Typically, the house service connections are reconnected robotically, requiring no excavation. 

Hundreds of millions of feet of CIPP are in service throughout the world today and it is considered the most widely accepted pipeline rehabilitation technology worldwide. CIPP has been installed successfully in continuous lengths of over 2,500 linear feet. 

CIPP Ultraviolet (UV) Light Cured 

Like heat-cured systems, UV creates a new pipe within the host pipe by curing a thermoset resin. The liner is typically winched into place using constant tension, then inflated using air pressure. A light train (see light-curing equipment section), including CCTV, UV lights, and infrared sensors is pull through the inside of the inflated liner before it is cured. The uncured liner is televised to determine if there are any defects before curing. The UV lights, on the light train, are turned on and the train is pulled back through, causing the liner to cure. Infrared sensors record the entire cure process 

Sectional CIPP 

A number of different trenchless methods are specifically designed for the repair of pipe joints and/or localized pipeline defects. They can vary in length from several feet to 30-feet and can be provided with hydrophilic-type seals installed at the ends of the sectional liner. 

Inverted sectional liners are available in a variety of lengths, sizes and thicknesses to accommodate the needed structural repair. The liner tube is vacuum saturated with an approved thermoset resin in the field and loaded into a flexible air inversion launcher. The launcher is pulled through the pipe to the point of repair; air pressure is applied causing the liner tube/bladder tube to invert through the defective pipe section. The liner is held under pressure until cured approximately two hours at ambient temperatures, or the liner may be steam cured, reducing cure time from two hours to as little as 30 minutes. 

Short sectional liners are saturated in the field, typically with an epoxy resin system, wrapped around an inflation packer and winched into the existing pipeline to the defective section. The packer is then inflated, and the resin is allowed to cure (typically two hours at 75 degrees F), depending on the temperature of the sewer. Heated packers can be used to speed up the cure time. 

The key to effective installations is to thoroughly understand the effects of temperature on the cure time for the short liner repair system used for patching pipe joints, pipe leakage, mis-cut service connections and any defect that may need repair in the pipeline. The short liner is installed in the pipe and positioned over the defective area. Once in place, ultraviolet light is switched on and the short liner is cured in less than 10 minutes. 

Folded Thermoplastic Pipe 

HDPE folded high-density polyethylene (HDPE) is commercially available in sizes ranging from 6 through 24 inches. The most common sizes used for sanitary sewer lines are 6 through 12 inches. The larger diameters are typically used to renovate pressure pipelines and culvert piping. 

HDPE is extruded in a round shape, folded and coiled on reels for delivery to the project site. In the field, the folded pipe is winched into place and then un-folded to fit tightly within the host pipe. The unfolding process is accomplished by the applying of air pressure and steam. To ensure a tight fit and no post installation movement of the liner, the contractor performs a precise re-rounding procedure, to anneal any residual installation stresses and stretch of the HDPE pipe. 

The liner is typically sized 2- to 2.5-percent smaller than the host pipe to ensure a tight fit, which limits the amount of stretching required and provides a consistent wall thickness. Typically, the house service connections are reconnected robotically requiring no excavation. 

Folded polyvinyl chloride (PVC), depending on the manufacturer, is available in sizes ranging from 6 through 24-inches and, in some cases, up to 30 inches. For sanitary sewer applications it is typically installed in sizes 6 through 15 inches. Bends up to 90 degrees can be accommodated. 

Folded PVC is extruded in a round shape, deformed, and coiled on reels for delivery to the project site. In the field, the coil of pipe is placed into a steam cabinet to soften the material, to allowing it to be winched into place. The folded PVC is then reformed to tightly fit the host pipe using air pressure and steam. 

House service connections are usually reconnected robotically, requiring no excavation. Materials are shelf-stable and able to be reprocessed. Thermoformed liners have been installed successfully in continuous lengths up to 1,500 linear feet. 


One of the older technologies, continuous sliplining pipe, is available in sizes ranging from 4 through 60 inches. It is installed using a number of different materials including HDPE, fused PVC, restrained joint PVC, ductile iron and steel. HDPE is still one of the more popular materials used with this technique. 

In the case of HDPE, lengths of round pipe are fused together to make up the length of the pipeline being rehabilitated. The fused liner is winched into place and the ends are sealed. Sliplining results in a smaller pipe being pulled into the existing pipe and some final capacity loss should be anticipated. In some cases, the annulus is grouted. Service reconnections are typically accomplished by excavation. 

Segmental pipe, available in sizes ranging from 12 to 102 inches, is accomplished using short lengths of profile wall PVC or GRP. Profile wall PVC is applicable to round pipe restorations, while GRP systems can accommodate round, egg, arch, and elliptical shaped host piping. The annulus is grouted, and the ends are sealed. Bends and transitions in size can be accommodated by the GRP systems, as well. Service reconnections are typically accomplished by excavation. 

Sectional pipe sizes range from 12 to 120 inches (or larger) with panel systems for larger sizes. This process is generally accomplished by inserting short lengths of PVC or GRP pipe or panels through existing manhole openings. The panel systems typically have two or more pieces making up a “ring” that is assembled inside the pipeline. After these systems are put into place, a non-shrink grout is pumped into the annulus. 

These systems are applicable to round, rectangular, egg, arch and elliptical shaped host piping. Bends and transitions in size can also be accommodated by the panel systems. Service re-connections are typically accomplished by excavation. 

Spiral-wound pipe is manufactured in narrow continuous strips of PVC with an interlocking edge that, when installed, locks the strips together as they are machine wound into the host pipe. The material has a ribbed structure and can be reinforced with steel rings for greater strength. PVC spiral-wound-in-place systems can be installed in sizes starting as small as 8 inches. 

A grout-in-place lining system (GPLS) is typically composed of a thin sheet of plastic, either PVC or HDPE, bonded to a structural grout layer. The GIPLS is a composite structure with the original pipeline. Owing to its method of installation (forms are typically constructed to support the grouting operation), GPLS is typically limited to worker-entry size piping. The exception to this is the PVC spiral-wound-in-place system, which can be installed in sizes starting as small as 8 inches. 

Spiral wound trenchless pipeline renewal is designed for and used primarily in large-diameter pipelines, typically worker entry. This process is unique as it can provide a customized structural solution to aging pipelines. 

Segmental panel systems are a series of molded or translucent PVC panels that, when assembled, form a new pipe or culvert within the existing damaged structure. A structural grout may be used to fill the annular space between the new segmental panel pipe and its host. This restores the structural strength of the original pipe, as well. The unique see-through walls allow visual monitoring of the grouting process. 

Water Main Lining 

Most water main lining technologies require that the existing pipe be thoroughly cleaned and prepared for application of the coating. Some cleaning techniques include hydraulic, mechanical, chemical, swabbing, scraping, pigging and air scouring. 

Cured-in-place liner systems are typically installed in pipe sizes of 6 to 24 inches. These liners span and seal leaking joints, pinholes and minor cracks. Services/laterals are reinstated from inside the pipe, with no excavation typically required, except for access pits. Resins used with potable water are typically NSF 61 approved. Installation lengths of up to 1,000 feet are not unusual and liners can negotiate bends in the existing main. 

Modified sliplining systems use PE or PVC material that is either site- or factory-folded or radially reduced prior to insertion into the host pipe. With the pipe liner profile reduced in size, allowing for easier installation, it is inserted utilizing techniques similar to those used in traditional sliplining applications. 

Air or water pressure and/or steam are used to revert the liner back to its original round shape, thereby forming a close fit with the host pipe. The new liner isolates the flow stream from the host pipe wall, eliminating internal corrosion and typically providing a full structural renovation solution. In addition, the new liner allows for service connections to be reinstated either externally to the new liner, or internally with newly developed robotic technologies. 

The sliplining method incorporates the installation of a smaller or reduced size steel, ductile iron, polyethylene, PVC or other pipe material inside the existing pipeline. Pressure-rated pipe capabilities can be selected for most main applications. 

In some cases, grouting is required to fill the gap between the host pipe and the new PE pipe. Very long lengths can be installed using this method. Service taps are typically excavated and directly reconnected. Sliplining can be applied in transmission and distribution mains of 6 to 60 inches in diameter.

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