Page 29 - Pipeline Pigging Technology

Pipeline Pigging Technology

PIGGING DURING OPERATION
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1 1 1 1
SEPARATION IMPROVING FLOW CORROSION METER
OF PRODUCTS EFFICIENCY INHIBITION PROVING

Multiproduct lines Removal of sand and Batching with Calibration of
wax from oil lines inhibitor flow meters
Dewatering
Clearance of dirt and Water drop-out
condensate from gas removal
lines

Fig.3. Pigging during operation.

no mixing takes place, a train of two or three batching pigs could be launched
with the new product in between.

Wax removal

Some crude oils have a tendency to form wax as they cool. The wax
crystallizes onto the pipe wall reducing the diameter and making the surface
rough. Both effects reduce the flow efficiency of the pipeline such that more
pumping energy must be expended to transport the same volume of oil.
A variety of cleaning and scraping pigs is available to remove the wax; most
work on the principle of having a by-pass flow through the body of the pig,
over the brushes or scrapers, and out to the front. This flow washes tne wax
away in front of the pig. The action of the pig also polishes wax remaining on
the pipe wall, leaving it smooth with a low hydraulic resistance.
There are alternatives to pigging for this application. For example, it is
possible to add pour-point depressants to inhibit wax formation, or it is
possible to add flow improvers which reduce turbulence and increase the
hydraulic efficiency of the pipeline. For a given pipeline, the choice will
depend on the reduction in pumping costs against the cost of pigging or
chemical injection, if indeed there is a net gain. Regular pigging does,

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