Page 224 - Pipeline Pigging Technology

Pipeline isolation - available options

PIPELINE ISOLATION:
AVAILABLE OPTIONS AND EXPERIENCE

IN EARLY 1989, new guidelines were introduced to the North Sea oil and
gas industry covering the requirement for and positioning of top-of-riser ESD
valves. The purpose of these valves is to prevent loss of product from the
pipeline in the event of topsides' failure, etc.
As such, many operators had to look at either fitting new valves or
repositioning existing valves. In order that this work can be undertaken in a
safe environment, there are two basic options:

i) displace all the product from the pipeline with an inert medium,
usually either water or nitrogen gas;
ii) provide localized isolation close to the worksite which would leave
the work area safe whilst leaving most of the pipeline full of product.

The options available for doing this and the method of determining the
most suitable solution depend upon a number of factors:

type of product;
length and diameter of the line and hence volume of product involved;
facilities for disposal of product;
time available for operations;
space availability at operational location restricting equipment deploy-
ment.

Bearing these factors in mind, various scenarios can now be considered,
and the advantages and disadvantages of alternative solutions examined.

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