Page 264 - Pipeline Pigging Technology

Gels for commissioning and production

(c) maximum line diameter and any changes in diameter;
(d) optimum displacement velocity.

4. Displacing condensatefrom lines'. Condensate, and other liquids can be
removed from the system by the introduction of gel pigs into the line, which
at the same time can be designed to lay down inhibitors, etc., on the pipe wall.
The efficiency of the laydown can be controlled by using a mechanical pig
which is slightly undersized to sweep the gel forward.

5. Increasing the sealing efficiency of mechanical pigs: Sealing mechani-
cal pigs can minimize fluid by-pass and therefore reduce pig wear. By using
a gel with a mechanical pig, pig wear can be reduced as the gels can be
designed to lubricate the pipe wall, which may be of particular importance
for long gas lines.

6. Aiding in the removal of stuck mechanical pigs: As mechanical pigs
travel down a line, wear on the cups can increase the by-pass of the drive fluid.
Movement will stop when there is a lack of differential pressure across the pig,
or when any debris ahead of the pig causes the pig to stop. Conventionally,
another pig is launched to remove the first, but due to the wear or debris build-
up this may also become stuck.
A gel pig pumped down the line which, depending on the situation, can
create a high differential pressure, would be more than sufficient to move a
stuck pig. If debris build-up has occurred, some of the gel will by-pass the pig
and entrain the debris which will allow the pig to move forward.

7. Laying down coatings on the pipe watt: Where specifically required,
inhibitors, solvents and chemicals can be laid evenly down on the pipe wall
to protect the system. This can be undertaken at the beginning of the
operational life, or during it, using gel systems which are compatible with the
line product.

8. De-oiling multi-diameter pipelines: In subsea applications, and other
situations where multi-diameter pipelines occur in a system, gels have been
successfully used to separate solvents and to de-oil and remove hydrocarbons
from the pipeline wall, allowing high-quality water injection to be undertaken
through the system. In these cases a simple gel train has been used and gel pigs
separate the fluids. It should be noted that the actual gel pigs which are built
for these jobs are built to be compatible with the fluids used in the system.

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