Underground Infrastructure - April 2023 - 36

Close-Fit Liners
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 follows.
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
36 APRIL 2023 | UndergroundInfrastructure.com
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 un-folding 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.
Sliplining
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 re-connections
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 re-connections
are typically accomplished by excavation.
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