Page 44 - Pipeline Pigging Technology

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especially if they have been applied in situ.
One camera pig operated by Geo Pipeline Services utilized a 35-mm
camera with a strobe light and wide-angle lens. The camera is mounted at right
angles to the pipe wall, and can be rotated to focus on any part of the
circumference. The instrumentation contains distance measurement, so that
the location of the photograph can be accurately determined.
A more recent development by NKK (Fig.5) has a different basic design, in
that the camera is mounted in the rear of the pig, providing a photograph
looking down the length of the pipe. It can be set to take photographs at pre-
determined intervals, or it can be fitted with a detector for girth welds, which
it automatically photographs once it has passed by. It, too, is particularly
useful for the inspection of in situ coatings.
It is capable of taking a large number of photographs in a single run. On one
run, for example, a 24-in (nom.) is understood to have covered a distance of
20km, and taken 13,000 photographs.

Video recording

Although there are a number of crawler-type devices attached to umbilicals
for the video inspection of short sections of pipe (often water mains), there
are no known ILI tools which are similarly equipped.

Metal loss

Metal loss and cracking are generally agreed to be the areas of most
concern[2J, and most of the money spent to date on ILI research and
development has been spent in these areas.
Two technologies have emerged as the preferred methods for the detec-
tion and measurement of metal loss:

magnetic-flux leakage (MFL), and
ultrasonics (U/S).

As with most technology, the basic principles are very simple. The trick is
putting them into practice...

Magnetic-flux leakage (MFL)

The simplest explanation of the principle of the MFL tools can perhaps
best be achieved by comparing it to the well-known horseshoe-shaped

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