Page 261 - Pipeline Pigging Technology
P. 261
Pipeline Pigging Technology
"Easy loading" pig
This pig has been developed by our sister company ITAC specifically for
offshore use during the final tie-in between a subsea pipeline and the platform
riser. Prior to the tie-in being carried out, the pipeline itself will have been
successfully pigged and gauged, as will the riser. Once the two are tied-in, it
is generally necessary to run a final gauging pig so that the tie-in spool will also
have been gauged. As it is virtually impossible to back-load a cupped or bi-
directional gauging pig into the open end of a subsea pipeline prior to tying-
in, it is usually necessary to run a gauging pig from the very start of the pipeline
through to the platform to gauge the tie-in spool. This is costly and time-
consuming, since the only relevant piece of pipe which needs to be gauged
is that of the short tie-in spool between the pipeline and the riser.
The "easy loading" pig is effectively a bi-directional pig using split discs
which initially are undersized to the pipeline bore. This allows it to be easily
inserted into the open end of the pipeline prior to the tie-in operations by a
diver. Once inserted, the discs are increased in size to form a tight seal with
the pipe wall by activating a spring mechanism within the pig body. Following
tie-in operations, the "easy loading" pig is then run through the tie-in spool
piece, up the riser and into the pig trap on the platform. This obviously saves
tremendous amounts of time and money, and especially so where the pipeline
is of considerable length.
SUMMARY
The art of pigging an operational pipeline is not an exact science,
especially in respect of pipelines which do not conform to normal param-
eters. It is hoped that this paper will give pipeline operators food for thought,
and to let them know that help can be on hand in situations where conven-
tional pigs are not appropriate. It is fair to say that nothing is impossible,
providing time, effort, expertise and money are available to solve the
problem.
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