Underground Construction - April 2018 - 38

Underground Construction Technology International Conference & Exhibition

EMERGING TECHNOLOGY

Codependency issues
Rather than independent, traditional SIPP technologies are
classified as "structurally interactive."
"The lining and host pipe
coexist, and share all external
loads, pressures and resistance
to failure events - generally not
in good ways," said Weisenberg.
"Basically, they are considered a
'Band-Aid' solution."
These not-so-good issues are
not conducive to extending the
design life of the pipe system.
"Current SIPP materials -
polymeric or, more specifically,
thermosetting plastics - have
high resistance to bending and
breaking, and the required rigidity, but are relatively brittle,"
said Lin Li, Ph.D., chief mechanical engineer at SippTech.
"Unless they are applied at considerable thickness, they can't
withstand internal working fluid
pressure, transverse shear and
overburden."
But increased lining thickness also has consequences,
Li explained. It leads to notably reduced pipe diameter and,
therefore, decreased flow capacities and greater pressure drop.
When applied in one pass, the
thicker materials often tend to
crack, primarily due to increased
heat and localized stress, and
significant loss of the polymer's
mechanical properties.
When a rigid polymeric material is adhered directly to the
inside of the host pipe, shrinkage during curing can cause
cracking or delamination. Direct
application also prevents the
rigid liner from surviving pipe
failure events. Once fractures or
remarkable deformations occur
in the host pipe where the liner
is adhered, the strains nearly
become infinite on the liner system, causing it to crack, fracture
or tear.
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APRIL 2018 | UConOnline.com

Another issue is material
fatigue over time, or low creep
resistance.
"In pressure pipe systems,
which are under long-term, continuous stress, the strength and
rigidity of polymeric/thermoset
materials initially decrease rapidly, and then gradually further
decrease with time during their
service life," said Weisenberg.
"Managing the lining thickness
doesn't improve the creep resistance, either, due to the nature
of the materials being used."
In addition, the polymeric materials yield to radial and longitudinal shrinkage during the curing
process.
"This will create a space (or
annulus) between the liner and
the host pipe," said Li. "When
pressurized fluid infiltrates behind the liner system at service
connections, terminations and
other discontinuities, the annulus renders the liner completely
inconsequential, as the host pipe
once again needs to resist all internal fluid pressures."
All of this interactive, or codependent, behavior precludes traditional SIPP technologies from
being a favored choice for the
rehabilitation of pressure pipe
systems.
Until now.

Novel approach
SippTech has pioneered a patent-pending approach, SippSteel,
that overcomes the structurally
independent deficits.
SippSteel is a three-component lining system comprising
two, polymeric materials - one
flexible and the other rigid - with
encapsulated, carbon-fiber, filament-reinforcement between
them. All these elements achieve
intermolecular adhesion during
installation, creating a three-layered structure inside pipe.
"The composite lining structure absolutely solves the inher-

ent SIPP problems and affords
the structural integrity to meet
the industry's structurally independent classification," said Li.
This is accomplished through
the use of materials that are
highly resistant to fatigue, buckling forces and creep. In addition,
innovative methods prevent
failures caused by adhesion, and
enable the SippSteel system to
withstand all operating pressure
and applied loads.
The flexible, or closed cell
porous (CCP), layer is virtually impermeable to pressurized
fluids and is applied directly to
the inside of a cleaned host pipe.
The rigid layer is bonded to the
CCP - not to the host pipe, as
in current SIPP technologies. In
this structure, the flexible lining
can stretch and yield to absorb
strains, and reduce the reaction
forces between the rigid liner and
host pipe, when pipe movement
or failure events occur.
"Essentially, the rigid liner
is suspended in the host pipe,
so external forces or strains are
not fully transferred onto the
rigid liner. Instead, they are
dissipated throughout the CCP
layer," explained Weisenberg.
"The CCP layer's low Poisson's
ratio, and ability to expand and
contract, continually fill and seal
any annular space created by
radial shrinkage of the rigid layer
during the curing process.
"And since it's impermeable,
the flexible material can prevent
fluid infiltration into any annulus at all discontinuities, such as
service connections in the liner,
therefore avoiding the potential
for hydraulic failures that often
occur with traditional SIPP and
other trenchless technologies."
Also unique to SippSteel is
a filament reinforcement layer
that further increases lining
strength and stiffness, compared
to today's unreinforced, rigid
SIPP materials.

"This extreme reinforcement
effect allows for a thinner rigid
layer - about 40 to 50 percent
less - and no reduction in diameter, versus thermosetting linings
without reinforcement," said Li.
"Additionally, the filaments resist a majority of the strain, thus
appreciably reducing stress on
the rigid liner caused by internal
pressure or exterior buckling
forces. Lower stress on the lining
material significantly extends the
working life of the liner against
fatigue and creep failure."

Beyond structurally
independent
SippSteel is more than just the
first structurally independent
SIPP lining system. It addresses other customer needs and
resolves systemic problems in
trenchless technology, in ways
that optimize cost-effectiveness
and efficacy of the rehabilitation
method.
As a thinner and more precise liner system, for example, it
uses less materials, reducing the
costs and time to install a much
stronger lining. Not only does
the thinner liner prevent reduced
cross-sectional diameter, it actually increases flow capacity.
Robotic installation of the lining, in one pass through the host
pipe, also saves time and costs,
and corrects limitations and inconsistencies of traditional SIPP.
"The SippSteel system employs
both individually specific and a
synergistic combination of computer vision, LIDAR, ultrasound,
RF, Wi-Fi, gyroscope, accelerometer and machine learning
technologies," said Julie Lee,
Ph.D., SippTech's chief electrical
engineer.
"Further assuring precise application, the robotic apparatus
is self-propelled, and all its mechanical functions are controlled
autonomously by internal sensors and computer vision," Lee

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Underground Construction - April 2018

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