Page 69 - Pipeline Pigging Technology

Pipeline Pigging Technology

(7) Small-diameter gas lines are very difficult to pig, compared to other
types of pipeline, and require special attention at the design stage.

Conclusion

All transmission lines should be designed for multi-purpose bi-directional
pigging (for cleaning and inspection), with permanent pig traps.
All well lines should be designed for multi-purpose bi-directional pigging
(for cleaning and inspection); they may be equipped with portable traps if
they form part of a multi-purpose grid.
All offshore lines requiring sphering facilities should be designed to
specific requirements in terms of the number of spheres to be launched, and
consideration must also be given to provision of sphere tees.

PIPELINE COMPONENTS

In terms of pipeline design costs for future pigging operations, provision
of pig-trap stations forms the largest capital investment of any specific
component. The pipeline itself, however, has specific fittings and valves
which require special attention during the design stage and even during
construction.

Tees

Tees can be divided into two types, sphere tees and barred tees. The
former are often used in piggable lines because of their constant internal
diameter.

Pig diverters

Pig diverters are particularly attractive to designers of subsea-well flowline
systems; their application can often reduce the high operational expenditure
of reloading a pigging station. A lot of development work has been done in this
area by BP in Norway; very limited actual experience is available.

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