Underground Construction - November 2019 - 34

REHABTECHNOLOGY

Operation and Maintenance
of Pressure Pipe Linings
NASSCO's Pressure Pipe Committee
EDITOR'S NOTE: This is the second installment of a three-part series
on pressure pipe presented by the National Association of Sewer Service
Companies (NASSCO) Pressure Pipe Committee. There will be an in-depth
program track on these topics and more at UCT, Jan. 28-30, 2020,
in Fort Worth, Texas.

Pressure pipe renewal technologies are designed for a variety
of applications, from AWWA Class I corrosion barriers to fully
structural, Class IV solutions. The main objective is to extend the
service life of the pressure pipe system, while minimizing the
carbon footprint and disruption to water supply.
A common question presented by utilities concerns
maintenance of these renewed buried assets. Specifically, how
future connections, repairs and cleaning are addressed without
compromising hydrostatic integrity of the pressure pipe or longterm performance of the lining system.

Cleaning of lined pipe
Due to their chemical composition and essentially smooth interior,
lining technologies are generally not susceptible to corrosion or
material deposits. However, should material buildup or bacteriological growth form within the pipe, it may be removed through
flushing or non-abrasive pigging. Hydraulic cleaning or water jetting at high velocity and pressure, abrasive pigging, drag scraping
and other mechanical cleaning methods are not recommended as
they can cause irreparable damage to most lining systems.
Flushing, a routine maintenance practice for unlined pipe, is
the simplest and most commonly used pipe cleaning method.
Conventional hydrant flushing is effective at reducing water age,
raising disinfection residuals and removing sediment. Unidirectional
flushing involves the isolation of pipe sections by closing valves and
opening hydrants to increase scour velocities, which in turn helps to
more efficiently remove sediment and biofilm.
Swabbing or non-abrasive pigging can be used to remove heavier
biofilm or sediment in lined pipe. Non-abrasive pigging makes use of
open cell, polyurethane, compressible (over-sized) foam pigs, which
are pulled through the lined pipe when the system is out of service
or propelled forward with water pressure. The pigs can be inserted
through points within the system (pig launchers) and received at
designated points downstream (pig catchers). Some hydrants can
be used as entrance and exit points for pigging operations. Nonabrasive pigging can be used on most lined pipes. Analyzing value to
risk should be made as there are times the pigs get stuck within the
pipe, requiring excavation for removal and repair.

End treatments

Valve insertion on a CIPP-lined pipe.

NOVEMBER 2019 | UConOnline.com

Mechanical internal pipe joint seals have a successful history for
repairing defective joints in pressure pipelines. These are typically
comprised of an elastomeric material and stainless-steel sleeve or
compression bands to provide a corrosion-resistant, watertight
seal with the necessary flexibility and elongation to accommodate
high-pressure applications and normal pipe movement. These products are also used to seal terminations of a lining system to prevent
fluid movement between the host pipe and a close-fit lining.
End seals or treatments are a common requirement for pressure
pipe and potable water applications, particularly with cured-inplace pipe (CIPP). The mechanical style end seals are expanded in
place, compressing the elastomeric seal against the liner and host
pipe to achieve water tightness. Each seal is sized to accommodate
the inside diameters of the liner and host pipe, and the installed
liner is trimmed back to a prescribed distance inside the host pipe

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Underground Construction - November 2019

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