Page 275 - Pipeline Pigging Technology

Pipeline Pigging Technology

pigs and high-viscosity gels. Basically a combination of gels, non-aqueous
fluid, and nitrogen is used to position the train in a pipeline and form a
isolation barrier. In one particular example it allowed the client to install 32-
in valves onto an existing pipeline without decommissioning the system. The
gels, fluid and nitrogen provide sealing to prevent by-pass of hydrocarbon gas
in the pipeline and prevent fluid loss from in front of the pig train into the
pipeline. The technique was developed during extensive full-size onshore
trials, where it was seen that modified conventional pigs could withstand high
differential pressures, in some cases in excess of 90psi. The offshore opera-
tion was deemed successful by all parties concerned; not only did the pig train
hold the required differential pressure, but also minimal fluid loss and no gas
by-pass was observed during the complete operation, which lasted in excess
of a month. Upon receipt of the pig train back at the platform the job was
deemed completed, and a complete success.

PACKER PIG

Nowsco has been awarded the license from Dowasue Industries of Canada
to market and operate its pipeline packer pig systems. Dowasue has had
success utilizing its umbilical/rodset packers in pipelines where high differ-
ential pressure isolation has been required. Nowsco's operational require-
ment, a modification of the existing technology, was necessary to enable the
systems to be acceptable for use in the applications envisaged in the North Sea
and Europe. At the present time, a 12-in free-swimming packer is available;
this can be dispatched from the pig launcher conventionally and, once at the
correct location, the pig can be stopped in the pipeline and the tool set. The
pig then can be used to isolate the pipeline against high differential pressure.
On completion, the tool is released and pigged either back to the platform or
along the length of the pipeline to the pig trap. Nowsco has been extensively
involved in the development of the systems required to make this tool usable
for fully-remote pipeline operations; this has included the development and
inclusion of tracking systems to ensure that the pig's position is known at all
times. For North Sea applications, it was considered that a replacement to the
existing setting control commands of the packer would have to be developed,
as well as equipment to determine and monitor the internal pressures within
the system.
We also required to know not only that the pig was set and holding
pressure, but that no internal seals were leaking and that the pig was not likely
to release itself unexpectedly. The setting command mechanism which was

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