Page 259 - Pipeline Pigging Technology

Pipeline Pigging Technology

less than the inside diameter of the pipeline. Protruding radially from the
circumferential edge of each disc are a number of steel pins which are
screwed into threaded housings anchored into the disc. The length of the pins
is such that the diameter across any two opposite pins is greater than the
inside diameter of the pipeline by up to lin, depending on line size. This
means that when the disc is travelling through the pipeline the pins are bent
back at a slight angle, which both assists in the cleaning action and also
compensates for any wear. The pins have hardened inserts to reduce wear to
a minimum and the inserts are radiused to prevent damage to the pipe wall.
Depending on the size of pipeline, four or six pin-wheel discs are attached
to a purpose-built steel body using appropriate retaining bolts. The pin-wheel
pig is always towed behind a conventional swabbing pig using a universal
joint to couple both pigs together. Each pin-wheel disc is orientated to ensure
that the cleaning pins on each disc are suitably offset from one another; this
offset ensures that the total surface area of the pipeline is cleaned. The use of
removable pins enables many options for wax/scale removal and cleaning to
be adopted, and on completion of each run any worn or damaged pins can be
simply replaced with new ones. By increasing the hardness of the poly-
urethane discs and/or the length of the cleaning pins, increased aggressive-
ness is achieved.
We always recommend a progressive approach when cleaning a pipeline
using the pin-wheel pig, in order to reduce the risk of a blockage which can
occur when too much material is removed from the pipe wall. It is preferred
that during the initial cleaning runs less than the entire internal surface of the
pipe will be cleaned, as it is better to remove wax or scale from the pipe wall
progressively during a number of pigging runs rather than trying to remove
it all during one run. This is achieved by running the pig with some of the pins
removed for initial runs, and then fitting more pins for each subsequent run
until all the pins are fitted. The design of the pin-wheel pig is such that little
or none of the wax or scale removed from the pipe wall will actually be
pushed forward by the pig itself; it will be left behind in the line. For actual
removal of this loosened wax or scale from the pipeline we use the pressure
by-pass pig.

Brush pig

This pig was developed for a client operating aviation spirit pipelines
where cleanliness is extremely important. The pipelines were being cleaned
using standard articulated pigs carrying steel wire brushes which were
relatively successful in removing larger dirt particles. However attempts to
improve the cleaning action by utilizing stiffer brushes merely removed the

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