Pipeline pigging
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United States of America Patent
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Aug 29, 2000
Grant Date -
N/A
app pub date -
Aug 20, 1998
filing date -
Sep 21, 1995
priority date (Note) -
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Abstract
A system for transporting a pig (28) along the interior of a pipeline (26), particularly for the purpose of installing a liner (12) in the pipeline by towing the liner behind the pig, in which a hydrostatic head is applied on either side of the pig and the head on the downstream side of the pig is reduced such that the pig is transported along the interior of the pipeline by the resultant pressure differential. Where the system is employed in a pre-existing subsea pipeline, the hydrostatic heads may be applied by means of risers (14, 24) and the pressure differential created by means of a pump (30) adapted to pump water out of the downstream riser (24). The liner may be pulled through a flooded pipe by means of a pig, cable, self-propelled pipe crawler, or by combinations of these. A further cable may also be employed to apply a back tension, and/or to limit the pulling force applied to the liner and/or to enable the liner to be pulled backwards.
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