Page 258 - Pipeline Pigging Technology

Specialist pigging techniques

ferrous debris is particularly high, then a more aggressive approach is
required so that the debris can be removed more efficiently and therefore
more quickly. We are aware of one pipeline which was so heavily contami-
nated with ferrous debris that the pipeline operator carried out a total of 43
separate pigging runs using a standard magnetic cleaning pig before all debris
was finally removed from the pipeline. A specialist pig would have reduced
the number of runs considerably.
Following investigation and exhaustive trials of the various types of
magnet available, our first improvement has been to mount and orientate the
magnets for maximum efficiency and performance. ,The second major im-
provement is the option of the addition of magnetic brushes which closely
resemble the brushes of an on-line inspection pig (working on the magnetic
flux leakage principle). The advantage of using magnetic brushes is that they
can be arranged in close proximity to, or even touching, the inside wall of the
pipe, due to their ability to flex when traversing bends or other restrictions.
Permanent magnets, on the other hand, have to be at least 3in away from the
pipe wall to avoid the pig fouling or becoming stuck in a bend. We have also
found that for optimum magnetic cleaning it is better to run a twin-module
pig, comprising separate bodies coupled together using a universal joint. In
some situations we will add a third body if circumstances demand it.
It is recommended that pipeline operators carry out a magnetic cleaning
programme well in advance of any form of on-line inspection operation, as it
is never known how much magnetic debris is present in a particular pipeline
until magnetic cleaning operations have commenced. If, for instance, it is
planned to carry out on-line inspection in perhaps one to two years time, then
it would not be too soon to commence magnetic cleaning immediately, since
once the line has been successfully cleaned, further contamination is not
likely to take place since ferrous debris is generally the result of construction
operations. An early magnetic cleaning programme will ensure that adequate
time is available to complete the operation efficiently.

Pin-wheel pig

This revolutionary pig has been specifically designed and developed for
the removal of hard wax and scale adhering to the inside wall of the pipe
which conventional cleaning pigs cannot dislodge. Although this wax or scale
is usually at its worst in the 4 to 8 o'clock position, the pin-wheel pig, through
its cleaning assembly, will give a 360° circumferential cleaning action, and
also allow for any rotation of the pig. The cleaning assemblies consist of a
number of heavy-duty polyurethane discs (referred to as pin-wheel discs)
which are up to 2in thick and have an outside diameter in the order of 3-4in

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