Underground Construction - December 2019 - 31

for partially deteriorated (interactive)
and fully deteriorated (fully structural)
gravity flow and low-pressure sewer pipe
and force main applications. This design
approach has been used extensively for a
wide range of products and applications
within the non-pressure and pressure
pipe sectors. Although it has served these
markets well, its premise is not applicable
to many coatings and linings, as it fails
to address critical pressure pipe design
elements. More specifically, ASTM F1216
was developed around isotropic (homogeneous) composites that are unbonded
to the host pipe. However, many pressure
pipe lining systems are anisotropic with
variable properties in the hoop (circumferential) and axial (longitudinal) directions,
and some rely on adhesion to the host pipe
for inherent hoop strength or to maintain
hydrostatic integrity.

Industry, standards evolve
As the pressure pipe lining industry
has evolved, so has the need for more
representative design guidelines and
standards. Currently, structural classifications of pressure pipe linings, from
Class I corrosion barriers to Class IV fully
structural systems, are loosely defined
in Appendix A of the Third Edition of
AWWA M28 Water Main Rehabilitation
with no design guidance provided, leaving
designers to devise their own means
of determining structural adequacy.
Through the efforts of the AWWA Pipeline
Rehabilitation Committee, a white paper
was developed with industry consensus
to better define lining classifications as
well as establish more specific design,
qualification and verification testing
and acceptance criteria. This committee
report, "Structural Classifications of
Pressure Pipe Linings, Suggested Protocol
for Product Classification" is scheduled
for publication in late 2019, and the bulk
of its content will be incorporated as a
stand-alone chapter in the upcoming
Fourth Edition of AWWA M28 targeted
for 2020 publication.
The primary keys to successful rehabilitation using pressure pipe lining systems
include:
* Owner/operator properly defining the
objectives of the project/performance
requirements

* Proper assessment and selection of
renewal technology to meet objectives
of the project
* Qualification of both the lining product
chosen and contractor to perform
the installation
* Effective communication with all
involved parties with the ability
to work together and adjust to
unforeseen circumstances
* Cleaning and preparation of the host pipe
* Implementation of quality controls
throughout construction
* Verification of proper installation
through established testing and
inspection methods (see Figure 1)
* Acceptance criteria and reconciliation
The ability of pressure pipe lining systems
to succeed is largely affected by its fit within, or adhesion to, the host pipe. Because of
this, acceptance criteria has historically relied heavily on post-installation inspection
to confirm fit and finish, as well as mechanical properties testing from representative
samples collected at the jobsite.

Adhesion
The pressure pipe industry has also
gravitated towards requiring adhesion
to the host pipe to ensure a watertight
finished product. Although in some cases
reliable adhesion may be desired for Class
II systems lacking hoop strength, or to
maintain hydrostatic integrity at services and lining terminations, there are
situations where adhesion is not desirable.
Applications - including those with broad
temperature swings or longitudinal movement due to expansive soils, frost heave
or settlement - are examples where lining
adhesion may actually be detrimental and
not accounted for in ASTM 1216 design
criteria. Consideration must also be given
to the host pipe material type, condition,
joining system, configuration, alignment
and in situ conditions; and their potential
impact on a lining system during the lining
inspection, installation and hydrostatic
testing process. For instance, if a host
pipe is structurally compromised or is not
anticipated to be able to withstand design
maximum allowable operating pressure
(MAOP) or hydrostatic test pressures,
catastrophic failure of the host pipe can
occur during testing or while in normal operation. In turn, this can compromise the

lining system, particularly a bonded one.
The need for a close fit lining system, or
one with minimal to no gap or interstitial
space between liner and host pipe, is well
substantiated, particularly for systems
designed for reliable adhesion to the host
pipe. A bonded lining system that does not
make close contact with the host pipe ID
about the entire circumference will endure
stress risers across unsupported areas and
can lead to failure. This can be prevented
through proper sizing and installation of
the lining system.
A properly designed close fit system
will be sized appropriately to form tightly
against the host pipe with the installed
geometry that reflects relevant short-term
and long-term type (laboratory) testing utilized for the basis of design. Interruption
of hoop integrity due to material oversizing
to achieve a tight fit and its impact on
pressure ratings of Class IV lining systems
should be considered in design and is
discussed in the AWWA white paper. This
further substantiates the need to capture
representative field samples for third party
mechanical properties testing to verify
installed properties. As a baseline requirement, enough material should be obtained
to perform tensile and flexural in the hoop
and axial directions.
As with any lining system application,
many situations cannot be easily replicated
or tested on the jobsite in terms of cause
and effect without utilizing destructive
means. That is, an owner's objective may
be to achieve water tightness at services,
withstand pipe movement or obtain a level
of reliable adhesion to the host pipe, but
may not have a way to confirm it in the
field. In such cases, demonstration testing
is recommended. These tests are typically
conducted by the lining system manufacturer, or as directed by the owner, to
simulate installed conditions and determine an end result. Specifics identified
during demonstration testing (e.g. surface
preparation, bond strength, allowance for
wrinkles or fins) that contribute to achieving positive results can then be required
during actual installation and field testing
to better ensure project success.
Attend UCT 2020 and the Pressure Pipe
Track to hear more Lessons Learned with
Pressure Pipe Lining Systems. *
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Underground Construction - December 2019

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