Page 33 - Pipeline Pigging Technology

Pipeline Pigging Technology

Internal coating

It is often desirable to coat the internal surface of a pipeline with a smooth
epoxy liner to give improved flow and added corrosion protection. A pigging
system has been developed to achieve this by first of all cleaning the internal
surface, and then pushing through a number of slugs of epoxy paint. The
alternative is to pre-coat most of the pipe and leave the welds uncoated.

Pressure-resisting plug

It is sometimes desirable to carry out maintenance on a pipeline without
shutting down and depressurizing it; this is particularly true of systems with
many users. In cases where there are not enough isolation valves, or it is the
isolation valves which are in need of repair, a pressure-resisting plug may be
pigged into the line to seal off the downstream operation. Present designs are
operated from an umbilical which limits their range and necessitates a special
seal on the pig trap door, but a remotely-controlled plug could be developed.

Piggable barrier valve

Subsea safety valves are used to protect offshore platforms against the
inventory of the pipeline in the event of a failure close to the platform; this
applies particularly to the larger gas pipelines. They comprise a subsea valve,
actuator, control system, umbilical and protective cover.
As a potentially-cheaper alternative, a piggable barrier valve could be used.
This would be pigged into position say 500m from the platform, and remotely
set in place. It would act as a non-return valve to prevent back flow of gas in
the event of an upstream depressurization. Its main disadvantage would be
the prevention of routine pigging.
Looking ahead, there is still a demand for improvements in pigging systems
to replace techniques which are often less than ideal. One can envisage
carrying out complete surveys of pipelines from the inside, monitoring wall
thickness, mapping position, subsidence, spanning and burial, and detecting
external damage, debris and anode wastage. One could look to the use of
down-hole and nuclear-industry technologies to develop remote-controlled
safety valves, repair operations, pressure-retaining plugs, and third-party tie-
in operations. In this age of space travel, there is still plenty of scope to
develop pigging technology to compete with more traditional techniques.

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