Underground Infrastructure - April 2023 - 35

REHABTECHNOLOGY
Technical Guide to Variations of
Close-Fit Liners for Mainline Pipe
Gerhard P. Muenchmeyer, P.E. | Principal, Trenchless Technology Education
Cured-in-place pipe (CIPP) has surpassed more than 52 years
of successful and diversified installations. Over those years,
the technology has advanced with development of new techniques
and products that have influenced cost, quality and
installation speed. Regardless of which materials and techniques
are used, the installation method, curing technique,
existing pipe, soil and pipe condition, and water in the pipeline,
all play a role in achieving a completed, quality product.
CIPP technology production generally includes a tube,
with an impermeable coating material and a resin product
combined into the tube, which is installed into an existing
pipeline and then cured into a pipe. A number of installation
choices, materials and curing methods are available to successfully
accomplish the production of CIPP. The technology
has evolved into several variations. Here is a look at the primary
CIPP methods actively in use today.
Cured-in-Place Pipe (CIPP) Heat Cured
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
UndergroundInfrastructure.com | APRIL 2023 35
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Underground Infrastructure - April 2023

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