Page 447 - Pipeline Pigging Technology

Pipeline Pigging Technology

Alternative approaches

We recognize that a number of options are available for rehabilitation and
repair methods that may even include replacement of long sections of
pipeline. The rehabilitation projects performed by the industry in recent
years illustrate the range of methods that have been used to assess the risks
and structural integrity and to perform repairs to return a damaged pipeline
to the condition that meets applicable design standards [4,5].
Many operators [6] report the combination of hydrotesting, repair by cut-
out, and recoating to be a practical approach for rehabilitation of pipeline
segments 5 to 30km in length. However, some concerns related to the
effectiveness of this approach have also been raised. A recent experience [7]
suggests that in some cases pipelines could have been replaced at a lower cost
than the cost of the rehabilitation involving cut-out repairs and recoating. This
kind of indication amplifies a need for an accurate and reliable assessment of
structural integrity of pipelines prior to making rehabilitation and repair
decisions.
Our own experience with two major pipelines containing many corrosion
indications has confirmed the usefulness of an approach that relies on sound
information about the condition of a line. Engineering critical assessment
(EGA) of corrosion damage accurately sized by an advanced ILI tool proved
to be the most cost-effective rehabilitation method. Less than ten reinforcing
sleeves, and no cut-out or recoating, were required in 1985 to re-establish the
structural integrity of about 800km of pipelines [8]. Both pipelines have
provided failure-free service since that time. The rehabilitation method
involving periodic inspection, EGA and repair continues to be more than one
order of magnitude more cost-effective than other rehabilitation alternatives.
The following sections of this paper outline the methods developed to
assess the risks and to direct inspection to pipelines where increased risk of
deterioration of structural integrity is indicated. A summary of the results
obtained in implementing the approach during the last three years is provided
as well.

RISK ASSESSMENT AND PIPELINE INTEGRITY

Methods that assess the risks related to structural integrity problems have
been described by authors representing British Gas pic [9,10], Tenneco Gas
Transportation Co[ll], and TransCanada Pipelines Ltd[12]. Each of these

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