Page 22 - Pipeline Pigging Technology

Why pig a pipeline?

WHY PIG A PIPELINE?

INTRODUCTION

Why pig a pipeline? This paper introduces a number of reasons for doing
so, together with a discussion of the advantages and alternatives. In general
terms, however, pigging is not an operation to be undertaken lightly. There
are often technical problems to be resolved and the operation requires careful
control and co-ordination. Even then, there is always a finite risk that a foreign
body introduced into the pipeline will become lodged, block the flow and
have to be cut out with all the operational expense and upset which would
accompany such an incident. The pipeline operator must therefore give
serious consideration to whether his line really needs to be pigged, whether
it is suitable to be pigged, and whether it is economic to do so.
The name pig was originally applied to Go-Devil scrapers which were
devices driven through the pipeline by the flowing fluid trailing spring-loaded
rakes to scrape wax off the internal walls. The rakes made a characteristic loud
squealing noise, hence the name "pig" which is now used to describe any
device made to pass through a pipeline driven by the pipeline fluid.
A large variety of pigs has now evolved, some of which are illustrated in
Fig.l. They typically perform the following functions:
separation of products
cleaning out deposits and debris
gauging the internal bore
location of obstructions
meter loop calibration
liquids' removal
gas removal
pipe geometry measurements
internal inspection
coating of internal bore
corrosion inhibition
improving flow efficiency