Page 242 - Pipeline Pigging Technology

Pigging and chemical treatment

PIGGING AND CHEMICAL
TREATMENT OF PIPELINES

THE PRIMARY purposes of any pipeline-maintenance programme are to
maximize flow ability and prolong the life of the piping system. The two most
common procedures for internal maintenance are chemical treatment and
mechanical cleaning using pigs. Although the procedures differ in nature and
effect, they are often used together to offer an efficient and cost-effective
approach to controlling significant pipeline problems. An understanding of
how each method works will give a clearer picture of how to combine the two
for a more effective, comprehensive pipeline-maintenance programme.

INTRODUCTION

Chemicals used in treating oil and gas pipelines, such as pour-point
depressants, flow improvers, corrosion inhibitors, biocides, and gas hydrate
prevention products, are often applied using pigs to enhance their perform-
ance and efficiency, and to supplement their action.
Pigs are used to remove paraffin deposits, apply corrosion inhibitors, clean
deposits from the line, and keep out accumulations of water. Water is the
source of several problems in oil and gas pipelines, in that it allows corrosion
to occur and bacteria to grow. Bacteria generate hydrogen sulphide, cause
corrosion, and produce plugging slimes and solids in the fluids. Of equal value
is the ability to remove sand, chalk, rust and scale deposits from inside the
pipeline, which can cause under-deposit corrosion, a major form of acceler-
ated corrosion, similar to pitting.
The following sections of this paper review the use of pigs in applying the
chemicals used to treat pipelines, with an explanation of the purpose of the
chemicals and how application by pigging enhances the performance of the
total system.

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