Page 37 - Pipeline Pigging Technology

Pipeline Pigging Technology

Offshore pipelines, even if they are not buried, invariably have concrete
weight coatings, and may be many hundreds of feet deep.
So, whether a pipeline is onshore or offshore, the only way a complete
inspection can be carried out is from inside the pipeline using "intelligent
pigs". Not surprisingly, in the United States, this is usually referred to as "in-
line inspection" or ILL
Apart from the obvious advantage of being able to inspect a pipeline
throughout its entire length without disturbing it, there is the added bonus of
being able to do so while it remains in operation. It is for this reason that in
Europe the operation is generally referred to as "on-line inspection".

AVAILABLE ILI TOOLS

The first commercially-available inspection service using ILI tools was
launched some 25 years ago. Since then there has been a dramatic increase
in the number of services available, and perhaps more importantly, techno-
logical development has led to extremely high levels of both accuracy and
reliability.
Many of the ILI tools currently being used are primarily for operational and
routine maintenance purposes; some, such as the British Gas elastic-wave pig
for stress-corrosion crack detection, and its burial and coating-assessment
tool, which should resolve many offshore problems, are believed to be
undergoing further development. However, the following is typical of the
information which can readily be provided for risk assessment, or to enable
decisions to be taken concerning rehabilitation or repair:

pipeline geometry-measuringovality, expansion, dents, wrinkles, etc.;
locating partially-closed valves or other restrictions;
determining bend radii and the location of tees;
pipeline alignment - locating and measuring movement or curvature of
the line which may be due to subsidence, erosion, earthquakes,
landslips, etc.;
visual inspection - providing pictures of the internal surface of the
pipeline;
metal loss - locating and measuring any loss of pipe-wall thickness due
to corrosion, gouges, or to any other cause.

Today, there are more than 30 different ILI tools in use by various
manufacturers, most of whom are members of the Pigging Products &

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