Page 234 - Pipeline Pigging Technology

Foam pigs

THE HISTORY AND APPLICATION OF
FOAM PIGS

WHEN A pipeline operator contemplates pigging a line, he must take
several factors into consideration:
the purpose of pigging
the operating conditions of the pipeline
the design of the system
the risks involved
the types of pigs available

If the operator is faced with conditions such as the removal of large
deposits of paraffin or scale, low pressures and flows, multi-dimensional lines,
reducing valves, or perhaps a "lose my job if I get a pig stuck" situation, then
the selection of pigs becomes an important decision. A list of available pig
designs is unfortunately not very long. The highlighted choices are spheres,
cup/disc pigs with steel or urethane mandrels, gels, and foam pigs. This paper
reviews the definition, history, various designs, and some of the unique
applications of the foam, or 'Polly Pig' as it is commonly called, and why it may
be the most versatile tool available to the operator.

WHAT IS A POLLY PIG?

In function, the polly pig is like most other non-intelligent pipeline pigs.
It is propelled through a pipe by a liquid or a gas, and performs work such as
dewatering, cleaning, or product separation. The body of the pig is made from
a special urethane foam that is flexible and wear-resistant. The open-cell foam
structure allows for the equalization of pressure throughout the foam body.
It can conform to dimensional reductions and pigging obstacles that may
prohibit the safe passage of other pigs. An elastomeric coating, similar to the
urethane material used for cups and spheres, can be applied to the external

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