Page 157 - Pipeline Pigging Technology

Pipeline Pigging Technology

distance sealing and lubricating effect. The additional pig included in the
middle of each batch is judged to considerably improve performance com-
pared with earlier common practice, where only single batches of gel were
used with the pigs interfacing with the gel. The dewatering train layout is
shown in Fig.5.
The main area of concern related to this long-distance pigging operation
is the breakdown of the dewatering train and excessive amounts of water
being left in the pipeline. If breakdown of the train should occur, two
possibilities exist:

start the drying operation taking into account the need for a longer
drying period; or
run a new dewatering train.

The dewatering train design will, however, be further improved during the
engineering phase. When selecting the pigs for dewatering, experience from
preceding operations will be taken into account, thereby further reducing the
risk of excessive pig wear and train breakdown.
Furthermore, the pigs will be improved. For instance, by reducing the
weight using lighter materials or by buoyancy tanks, or by equipping the
critical pigs with wheels to support their weight, it should be possible to limit
the pig wear with respect to the pipeline ID, and thereby considerably reduce
any by-pass and the consequences of excessive wear.

PIG DEVELOPMENT AND TESTING

The pigs to be used during intermediate testing, precommissioning and
commissioning will be purpose-made to fit the Zeepipe requirements. Pig
manufacturers will be approached for development and design work, result-
ing in the fabrication of a prototype pig(s) which will be subjected to an
extensive testing programme.
Several possibilities for reducing wear and improving sealing capability
will be considered:

Reducing the weight of the pig by employing lighter materials: Disc
wear is partly dependent on pig weight; heavier pigs also have a
tendency to develop asymmetric wear. As the pig body is usually
made of steel, there is a potential for improvement through weight

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