Underground Construction - March 2019 - 25

Pipe Freezing
Liquid Nitrogen Freezing Solves Pipe-Cutting Problems
Ice recently helped solve a
major environmental problem
in a remote area of Oregon.
Construction of a new access
to the Willamette River was
necessary, as part of a plan to
replenish a salmon hatchery, but
this necessitated partial removal
of a 10-inch pipeline that was
causing an obstruction.
The pipeline had been isolated
and abandoned previously
and filled with water that had
probably become polluted.
Simply cutting the pipeline
would release more than 1.3
million gallons of contaminated
water into surrounding land
lying within a sensitive,
environmentally protected area.
A decision was made to use
liquid nitrogen to create ice
plugs and isolate the small
section of pipe causing the
obstruction. The pipe could then
be cut, releasing only limited
contaminated water and this
could be contained and removed
from the site.
Pits were excavated on either
side of the access exposing the
pipe, and the anti- corrosion
coating was removed. Freezing
commenced in the early morning
in record-high temperatures,
combined with little to
no shade in the area.
The pipe was cut on both sides
and the remaining contaminated
water drained to disposal
containers for removal. Welders
quickly capped the open ends.
The freeze equipment was shut
down and the ice plugs allowed
to thaw naturally. The proposed
river access refurbishment
was allowed to continue the
following week, bringing life
back to a vital natural habitat.

Equipment
Equipment employed for the
freezing operation was an AccuFreeze System, manufactured by
Huntingdon Fusion Techniques
HFT, a United Kingdom-based
global leader in gas weld-purging
techniques, partnered with its
Melbourne, Fla., U.S. Division,
HFT COB USA.
The procedure creates an
in-line ice plug capable of
withstanding 140 bar in pipes
up to 12-inch diameter and
can be modified using available
options to handle even larger
diameters. A specially designed,
insulated aluminium jacket
is placed around the required
section of pipe to be frozen.
An advanced temperaturemonitoring unit controls the
surface wall temperature of the
pipe to accurately and safely
create a short ice plug that does
not extend outside the jacket.
Accu-Freeze is automatic
and can be remotely operated,
making it attractive for use in
nuclear applications and other
locations where engineer access
must be restricted. Freezing
using liquid nitrogen is effective
in temperatures down to minu184-degrees Fahrenheit. It's
suitable for isolating sections
of pipe carrying petrochemicals
so that valves and other control
devices can be removed without
the expense and delays involved
in draining the system.
The concept of isolation
using liquid nitrogen had been
used in the past to resolve
major problems with a NASA
launch vehicle and inside a large
chemical plant.
Pipe freezer technology
allows fluids to be frozen below
minus-238-degrees Fahrenheit
using liquid nitrogen. Specially
designed insulation and feeder

hoses used to deliver coolants
and continuous temperature
control during the freeze
operation can be incorporated.
The use of freeze technology
affords the opportunity to
isolate sections of pipework
for maintenance, repair and
replacement of valves, couplings
and instrumentation. With no
draining of the system required,
there is no need to disrupt
production beyond the time
needed to freeze and undertake
changes. *
FOR MORE INFORMATION
Huntingdon Fusion Techniques
HFT, (800) 431-1311,
huntingdonfusion.com

Exposed pipe in readiness
for freezing operation.

Accu-Freeze frozen clam shell
on pipe.

prevent this

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Underground Construction - March 2019

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