Page 260 - Pipeline Pigging Technology

Specialist pigging techniques

protection of the corrosion inhibitor from the pipe wall, which was unaccept-
able. We designed and produced a unique brush pig using nylon brushes
impregnated with carborundum grit. During trials, it was found that the brush
pig was extremely efficient in removing very fine debris from the pipeline,
thereby considerably increasing the times between filter changes at the
airfield due to the increased cleanliness of the product.
Due to superior cleaning ability, far in excess of a conventional cleaning
pig, we now use the brush pig in our service operations for clients requiring
as clean a pipeline as it is possible to achieve. However, due to the efficiency,
we generally adopt a progressive cleaning approach, starting off with conven-
tional cleaning pigs and only using the brush pig for final cleaning once the
majority of debris has been removed from the pipeline.

Shunting pig

This pig is basically a three-section articulated pig which has been
specifically developed for the removal of stuck or lost pigs from pipelines. Our
experience has taught us that if a pig does become stuck or lost in the pipeline
there is little point in running a second pig of similar or identical design, since
this pig is likely to succumb to the same problem as the first pig and also
become stuck or lost itself. What generally happens to a pig which is required
to push a stuck or lost pig (usually in pieces) is that the additional effort of
removing the debris causes the second pig to become damaged itself. Using
a three-section articulated pig, we recognize that the first section will
probably become damaged to a considerable extent as it pushes the debris
ahead of it, but drive will be maintained because of the second and third
sections which never come in contact with the debris being pushed out.
Additionally, the shunting pig is deliberately made to be extremely heavy to
give increased momentum, since lightweight pigs are of little or no use in
removing stuck or lost pigs from pipelines. Much attention is paid to the
design of a shunting pig so that there is no metal-to-metal contact between the
shunting pig and the debris being pushed out, and this is achieved by fitting
a hard polyurethane bumper ahead of both the pig body and the front cup.
The shunting pig is also equipped with permanent magnets for tracking
purposes, together with a battery-operated electro-magnetic device for
positive location when stationary.
A further use for the shunting pig is in pipelines which are particularly
hostile to pigs, thereby requiring a much stronger construction of pig. The
extended length and increased number of cups and discs substantially
improves its performance in difficult conditions.

241