Underground Construction - February 2020 - 33

A street view of the 42-inch drum pit transfer hose.

cost and disruption would be astronomical to dig up the old pipe and
lay new pipe. To replace this section of pipe conventionally would
have cost of millions of dollars and created massive disruption."
Using a trenchless method was significantly less costly than
open cut construction would have been, even if possible,
Wickersham said. The street remained open during the project.
Live, closed-circuit-television inspection, months before the
project's start, confirmed the internal conditions of the pipeline,
including geometry, anomalies and fittings. All tests were performed
under live conditions without interruption of service to customers.

Cleaning
Before the lining process started, cleaning of the pipe was
essential. The large diameter of the pipe and its multiple bends
presented challenges in the time required to clean, cleaning
effectiveness and grit recovery.
Wickersham said the current cleaning method for smaller-diameter pipes is to pull a sandblasting cleaning head through the pipe,

prior to engaging the grit blast. Once the head is confirmed at the
start location within the pipe, the grit blast is initiated, and the
head is pulled back at a slow rate. While effective, it takes time to
pull the head in with a winch.
"PPM," he explained, "identified a self-propelled robotic sandblasting head with an electric motor for internal cleaning of pipelines in diameters of 36 inches and larger. No staging is required.
Using it, the head went in and the crew was cleaning within 10
minutes. It worked brilliantly. Its video camera allowed real-time
views of results as cleaning progressed. The crew affectionately
named the device 'The Beast.'"
To remove all dust and particles from the pipe, extensive testing
and reconfiguration of the vacuum equipment was performed to
optimize velocities impacting flow rates and minimize expected
extraction difficulties, due to the unusual "U" configuration of the
pipeline that went down and back up a steep embankment.
"We deployed two dust collection units with a total 64,000 CFM
air flow that proved to be the 'silver bullet' allowing complete grit
recovery," Wickersham said. "This was a milestone considering the
pipe diameter and geometry."
Based on lessons learned from the previous world record of
lining 36-inch pipe, a special inversion drum was designed and
fabricated that increased capacity. The use of a transport hose
significantly reduced above-ground equipment footprint during
curing. These modifications reduced equipment set-up time and
increased crew efficiency.
The 620-foot-long liner was inverted through a total of seven
bends (two of which were mitered steel bends within a short section
of steel) and a drip pot with a 48-inch gap that was bridged with an
internally installed, forged steel structural reinforcement sleeve.

Fast work
Lining was completed in only three days, and the overall project
was finished two-and-a-half weeks ahead of schedule.
The Starline liner was developed by Karl Weiss, a German company with extensive experience in natural gas renewal applications
and subsurface engineering. The patented technology utilizes a
liner that is bonded to the host pipe with a special epoxy. The twopart epoxy is mixed onsite and applied to the liner immediately
prior to the installation. The liner/epoxy then cure at ambient
temperatures, typically within 24 hours during warmer months.
Advantages of the lining include that it does not significantly
reduce pipe capacity, and rehabilitation of pipe requires minimal
excavation and restoration. Also, gas cannot because the liner
uniformly bonds to the pipe.
UConOnline.com | FEBRUARY 2020

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Underground Construction - February 2020

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