Page 251 - Pipeline Pigging Technology

Pipeline Pigging Technology

polysaccharide outer layer [8] which can effectively filter biocides and other
chemicals. This protective layer can defeat routine bacteria control pro-
grammes based upon simply batching bactericides through the line.
Pigs used in conjunction with a biocide programme can be very effective.
A pig should first be run to remove substantial build-up of water. Wire-brush
pigs can be used to scrape and scratch the bacteria colony outer layer, and
remove bulk bacteria growth from the pipe wall. This prepares the pipe
surface for the application of biocides, enabling the biocide to reach and
destroy the colony, and reducing the volume of bacteria to be treated. Nylon-
bristle brushes are available for coated and plastic-lined pipe systems. Sealing
pigs can then be utilized to batch a slug of biocides, enabling maximum
exposure to the affected areas.
This approach has proven very successful in treating an 8-mile long, 12.75-
in gas condensate pipeline which was infested with SRB. A programme was
developed where a drum of biocides mixed with 50brls water was pumped
into the line, followed by a pig to batch the liquid through the system. After
several months of this programme, it was apparent from monitoring the
pipeline that the bacteria were continuing to grow. A new procedure was
adopted where a wire-brush pig polly pig was inserted into the line, 120brls
of water containing biocide were pumped in, followed by a sealer pig. Since
this procedure was adopted, no further evidence of microbiologically-in-
duced corrosion was found.

SELECTION OF PIG DESIGN

As in any pigging application, the best results are achieved when using a
pig design which is suitable for the required procedure. Using the wrong
equipment when combining a pigging and chemical programme can waste
expensive chemicals, leave pipe surfaces insufficiently clean, and in the long
term actually contribute to pipe failure. For the applications discussed in this
paper, cleaning pigs and/or sealing pigs should primarily be used.
Chemical treatment is most effective when applied to a clean pipe wall.
For this reason, pipeline operators should ensure that aggressive cleaning pigs
be run in lines that have the potential for wax or scale deposition. Although
any type of pig offers some degree of cleaning, it is recommended that pigs
with heavy-duty scraper cups, stiff guide discs, and/or wire brushes, be
utilized when any deposits are expected. Well-established build-up such as
hard scale, wax or colonies of bacteria, usually are left unaffected unless well
"scratched" by the passage of a pig. Conical cups and spring-loaded blades are

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