Underground Construction - September 2019 - 41

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avoidable conversations about whether their CIPP
installations were to be accepted by the asset owner
or not, due to the existence of liner features that were
perhaps incorrectly identified in PACP as failures. The
updated PACP Version 7 has provided some relief to
these situations; however, the question still remains:
at what point is a liner's feature constitutive of a defect
that would affect the proper operation of the pipeline?
PACP defines "Lining Feature Blistered" (LFB code)
as when "the pipe liner interior coating contains
pockets, sheets, etc. (e.g. air, resin, water, solvent)
that causes a blistered effect on the inside surface of
the liner. This effect can also be produced when the
internal heat of a CIPP liner affects the stability of the
internal lining coating material during the initial curing
process." Whether these kinds of pockets or sheets are
contained within the liner itself, as opposed to being the
appearance of a blister on the liner's coating, is what's
crucial here. NASSCO's Inspector Training Certification
Program (ITCP®) provides helpful guidance here, as the
ITCP manual does distinguish between a blister on the
coating of a liner and the presence of a blister due to a
defect occurring internally within the liner.
In the case where CIPP is installed with a thermoset
resin that is steam cured, it is sometimes common to
observe a blistering effect on the coating of the liner,
and according to the ITCP manual, "steam blisters may
be cosmetic in nature" and may not demonstrate a
failed condition. The manual also states that "the CIPP
should be tested to verify required physical properties."
Many factors can cause this effect, and some have little
or nothing to do with the methods or skill of the installer.
One example of this would be the existence of a point
repair in the host pipe, where inverting and curing a liner
through a segment of host pipe which had PVC from a
previous point repair can cause the interposing PVC to
act as an insulator, generating excessive heat from the
exotherm reaction and can cause blistering.
In all CIPP applications, it is important to follow relevant
ASTM guidelines for installation and testing of a liner's
properties to ensure design specifications are met.
Such tests should be used to inform whether an asset
owner or engineer is to approve or disapprove of a
particular CIPP installation when the LFB code has
been used in the PACP survey.
Regarding the use of the Lining Feature Wrinkle
(LFW) code, it is again useful to reference the ITCP

manual, which states that "the wrinkle, typically solid
throughout, is not desirable and may be acceptable
if it does not disrupt or impede the normal flow
characteristics of the new CIPP. If the wrinkles are in the
invert or lower portion of the pipe and will interfere with
the flow characteristics of the pipeline, or they exceed
the standard specification in the contract documents,
they need to be removed or repaired as applicable."
(ITCP Chapter 3; Section 11.1; pg. 64).
Wrinkles can be endemic to CIPP and should not
be considered as inherently defective, because they
are primarily a function of the host pipe's variability
in circumference along the reach of sewer that is
being lined. Due to many of the mechanisms which
cause structural deterioration of sewers, variability in
circumference is a common condition in pipes where
renewal using CIPP has been recommended. Said
another way, the deteriorated host pipe's geometry (or
out-of-roundness), if it contributes to the decision to
use CIPP in the first place, should also not be a factor
preventing the CIPP post-install from being accepted by
the asset owner or engineer.
According to the ITCP manual, pertaining to wrinkles
outside the flowline of the pipeline: "Wrinkles/fins in the
height up to a maximum of 5% of the inside diameter
of the host pipe are generally acceptable." The PACP
operator conducting the survey should pay close
attention to the degree to which the LFW intrudes into
the cross-sectional area of the pipe. Another useful
distinction in evaluating a wrinkle is its location relative
to the flow line.
Specifically, the presence of wrinkles that do not
exceed 5% of the inside diameter of the pipe "may be
generally acceptable" according to the ITCP manual,
and even those that do exceed 5% "particularly those
of a longitudinal configuration, may be acceptable
and should be evaluated by the project engineer for
acceptance on a case by case basis" regarding what
the actual impact would be on the pipe's hydraulics,
taking into consideration whether the wrinkle is
longitudinal (parallel to the flow) or circumferential, as
well as other factors such as inclination of the pipe and
flow levels.
Hopefully this analysis can be useful as a tool for CIPP
installers, consulting engineers, and sewer utilities
who utilize PACP to evaluate the condition of pipes
rehabilitated with CIPP methods.
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Underground Construction - September 2019

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