Page 43 - Pipeline Pigging Technology

Pipeline Pigging Technology

work done in the aerospace industry, it is also not surprising that they have
been successful in this role.
Although HRE was also one of the pioneers of this method, a lot of
development has recently been done by Pigco Pipeline Services in Canada on
its "Geopig" (Fig.4). As with most modern ILI tools, the technology is very
advanced, and a very detailed description of the Geopig was given in a recent
paper[31 (see pages 343-364).
The heart of the system is a "strapdown inertial measurement unit" or
SIMU. This contains both accelerometers and gyros which, when coupled,
provide input for computing pipeline curvature, the orientation of that
curvature, and its position.
The SIMU is installed inside the pig body, which in turn is supported on
elastomer drive discs. Although this ensures that the SIMU will travel in close
approximation to the centreline of the pipe, it is recognized that the pig's
pitch and heading will not coincide with the slope and azimuth of the
pipeline. The pig is therefore fitted with a ring of sonars at each end of the
inertial system, to provide constant readings of the pig-to-pipe attitude.
Odometer wheels are used for distance measurement, and the instrumen-
tation also provides for the measurement and recording of the pipeline
geometry such as diameter reductions, etc.
Large amounts of data are gathered, and it was quickly recognized that hard
copy was, in effect, unmanageable. Instead, a PC software package has been
developed with the data contained on an optical disc. This allows for rapid
retrieval or manipulation of the information, and effectively eliminates errors
in interpretation.

Visual inspection

Photographic

The results obtained by some of the early ILI tools were often (and with
some justification) regarded with scepticism, and it was felt that visual
confirmation of a particular feature would be helpful. However, pictures can
only be obtained in good visibility, which limits the use of this technique to
relatively-clean, clear gas or liquids. In addition, the information provided by
ILI tools quickly became more detailed and reliable, so there was no need for
visual inspection to confirm the results. These factors combined to limit the
use of visual inspection.
There are still, though, many situations where a visual inspection can be
very useful. One area in particular is for inspecting the condition of linings,

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