Underground Infrastructure - May 2023 - 31

Rehab Technology
not at much risk of pushing everything up front and causing a
blockage worse than what you had before you started. "
To produce the ice slurry, trailer-mounted ice generators
mix and freeze up to 2,700 gallons of slurry overnight and
maintain its 24-degree temperature with a combination of water
and a freezing depressant. Since ice pigging was originally
developed for cleaning food industry pipes, food-grade table
salt was selected as the original depressant and is still commonly
used for cleaning water pipes.
Once the slurry is produced, it is transferred to a 10-ton delivery
rig that connects to an inlet on the system, such as a hydrant.
[FIGURE 1] Because the ice pig enters and exits through
existing inlets and outlets, specialized launch and retrieval stations
are not required as with mechanical pigging or swabbing.
A minimum 2-inch connection will suffice.
Customer service isolation usually is not necessary either.
Because the pig is an ice slurry, not a solid pig, it can't get stuck,
and an ice pig can negotiate pipe bends, diameter changes, broken
gate valves, and in-line butterfly valves without affecting
the cleaning process.
After exiting the water pipe, the slurry passes through a
truck-based flow analysis system that monitors flow, pressure,
conductivity, turbidity and water temperature. A written
post-project report is provided with the results of chemical,
biological and mechanical analyses.
Ice pigging has also been effective for cleaning sewer force
mains [FIGURE 2]. In this application, it might be necessary
when ice pigging sewer force mains to turn off lift station
pumps for up to 20 minutes while the ice is being injected.
In the case of sewer siphons, a technique was developed using
inflatable packers to seal the pipe and create a pressurized
environment before injecting the ice slurry. [FIGURE 3] When
the plugs are pulled, the cyclonic action takes over to provide
risk-free cleaning.
Pros and cons
Comparing ice pigging with traditional cleaning techniques,
Treloar is especially dismissive of UDF, citing poor results due
to low water shear, large volumes of wasted water, required high
velocity and failing to remove all sediment.
In addition to being more drought-friendly - a matter of
greater concern in southwestern states - ice pigging will pass
through butterfly valves. Post-cleaning disinfection is not required
since it uses only a brine solution. Bacteriological samples
also are not needed, although they are often taken.
Other methods, such as jetting and air scouring, fare comparatively
better, although they may be too aggressive for some
pipes in poor condition and may be limited by hose lengths. Ice
pigging is less aggressive while still being effective.
But ice pigging has its limitations. It's not effective at removing
calcified deposits or tuberculation, the formation of
iron oxide mounds on a pipe's interior due to bacteria-driven
corrosion, although some would consider its removal more of a
rehabilitation project than a cleaning.
It's also impractical for large-diameter pipes because of
FIGURE 3
the speed and capacity of the ice-producing equipment. The
maximum length of pipe Treloar has cleaned in a day with
one 10-ton tank load of ice was 2.3 miles of 6-inch PVC pipe.
Smaller pipe allows greater distances per day, but lengths are
dramatically reduced on larger pipes. Pipes below 24 inches in
diameter are fair game.
While ice pigging may be more expensive on a dollar-to-dollar
comparison, Treloar contends it offers greater
value compared to even flushing.
" Although people think flushing is inexpensive, if you compare
how much sediment is removed per foot, then ice pigging
is going to be a lot more cost-effective because flushing
just doesn't remove sediment, " Treloar said. " It's also more
environmentally friendly and more drought-friendly, because
we're not going to waste loads of water, which is getting really
precious. " UI
UndergroundInfrastructure.com | MAY 2023 31
FIGURE 1
FIGURE 2
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