Page 437 - Pipeline Pigging Technology

Pipeline Pigging Technology

operators are adopting formalized, quantitative schemes, which can be used
to great effect in ensuring that the most appropriate inspection, repair and
maintenance programmes are employed over the life of a pipeline.
Once the decision has been made to perform an on-line inspection survey
of a pipeline, considerations of technical standard and cost become the focus
of attention. The two factors are closely related, since the inspection phase
of a project cannot be financially divorced from the consequent costs of
remedial work and the subsequent costs of pipeline maintenance. The
inspection service must, therefore, be regarded as an integral part of pipeline
maintenance, with the accuracy and repeatability of the service determining
the final out-turn of maintenance costs.

Preparation

Before a pipeline is inspected, it is prudent to perform a detailed review
of its engineering records to gain early information about it's suitability for on-
line inspection. This phase is usually complemented by extensive discussions
with the pipeline operator, and an on-site survey of the line by a British Gas
engineer. Once it has been established that the pipeline is suitable for the
running of an inspection tool, the in-field operational phase can begin.

In-field tool running

This phase comprises a series of operations, carried out in a specific order
to ensure the successful running of the inspection tool. The first part entails
the running of cleaning and bore-proving pigs, to provide optimum condi-
tions for inspection; the second part involves the running of the inspection
tool itself.
Extensive preparatory work ensures the timely execution of this part of
the service, together with specialized handling equipment to simplify the
insertion and extraction of pigs. In addition, the detail of inspection tool
design provides a virtual guarantee that the tool will pass through the pipeline
without becoming stuck or damaged.

Validation of survey data

Of particular importance in the field is the post-inspection validation of the
survey data, and this occurs following the withdrawal of the magnetic tape
store from the on-board tape recorder. During the inspection operation, data

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