Boring - Trenchless International

Cleaning pipes with pigs
by Lyndsie Mewett
Pipeline Pigging and Integrity Management
pipe cleaning
April 2010 - Trenchless International
Cleaning pig uses
Cleaning pigs have a variety of uses
including the removal of debris, paraffin
and millscale, the verification of the ovality
of the pipe, corrosion control and dewatering
during hydrostatic testing. During
construction pigs are used to remove dirt
or general construction debris that may be
inside the pipe as it is being assembled.
Pigs are used in the hydrostatic testing
process, pumped through the pipeline
with water, as a tool to expel air from the
line. Following this, a cleaning pig is used
to dewater and dry the pipeline before
commissioning.
During operation, cleaning pigs are
extremely important because they are
able to remove substances that may
obstruct flow within the pipeline, or damage
the pipeline itself, while still allowing
continuous operation of the pipeline. In
addition, through the removal of debris,
cleaning pigs ensure that a pipeline maintains
its maximum efficiency.
Because of the pigs’ varied uses and
the differences inherent in each pipeline,
cleaning pigs are available in a number of
different designs. The pigs can be of a light
or heavy density, depending on the function
of the pig. A pig of heavy density may
be put through a pipeline first, followed by
lighter density pigs.
Foam and polyurethane pigs
Foam or polyurethane pigs are available
in various densities and shapes. They can
be bullet shaped, have concave ends or
flat ends, be jelly coated on the outside or
sometimes have a silicone carbine coating.
In addition, some foam pigs can have
a crisscross pattern with silicone carbine
implanted in the pig.
Coated foam pigs are used for general
cleaning, whereas the more abrasive coating
of silicone carbine is used for cleaning
lines with build-up. The crisscross pattern
is also used for medium-length runs in pipe
where extra abrasion resistance is required.
The shape of the pig dictates how fast it
travels while in the pipe. The travel speed
in turn determines the force of the pig’s
What’s in a name?
Theories have abounded as to the meaning of the word ‘pig’. These days,
many claim it stands for ‘pipeline inspection gauge’, however it seems that this
term only came into being after the word pig was already in use in this context.
A likely theory is the high-pitched squealing sound made by the early devices
as they scraped the inside of a pipeline resembled the squeal of a pig. Other
theories include the brushes resembling the hair of a pig, some early devices
being made in part with pig skin and the appearance of the device once it had
finished its job, covered in dirt like a pig.
cleaning edge, with higher speed pigs
being able to remove tougher debris.
Foam pigs are flexible, enabling them
to compress and expand so that they can
travel through multi-diameter pipelines
and navigate bends in the pipeline.
Light-density foam pigs are used to
pass through the pipeline first because
their open-cell foam aids the drying
of pipelines after hydrostatic testing.
Medium-to-heavy density foam pigs are
used during pipe construction, start-up,
during operations, for maintenance and
emergencies.
Solid polyurethane pigs are designed
to be used in batching or displacement
of fluids in petroleum, chemical or process
industry pipelines. Batching refers
to when a pig is used between batches
of product, such as between petrols and
various other types of fuel. A displacement
pig displaces one fluid with another and is
used in the commissioning process.
Mandrel pigs
Mandrel pigs have a metal body with
seals, scraper cups or discs on their
exterior. The pigs can be used for an
ovalarity check or for gauging the internal
diameter of the pipe, to clean the
line, as a sealing pig, as a combination
cleaning/sealing pig, for batching,
dewatering and drying after testing.
Extra discs can be provided to attach
to mandrel pigs to scrape extra debris.
For example, crude lines can get a
heavy wax build-up and sometimes
require extra discs on the pig to clean
the line. Additional cups and brushes
can also be acquired.
The world’s most respected
pigging conference is coming to
the Asia Pacific region
www.clarion.org
CONFERENCE • TRAINING COURSES • EXHIBITION
8-11 November 2010 • Crowne Plaza Hotel • Kuala Lumpur
April 2010 - Trenchless International
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