Page 454 - Pipeline Pigging Technology

Risk assessment and inspection for integrity

Fig.9. Distribution of programme costs (1988-1990 incL).

in qualitative agreement with the predictions of the fault-tree analysis. By
completing the ILI projects, it is considered that the probability of an outage
caused by corrosion has been essentially eliminated for those pipelines, so
that the position of these pipelines on the economic risk diagram is reduced,
as shown by points 1, 2 and 3 in Fig.8. In the three-year period from 1988 to
1990, we will have inspected a total length of about 1200km with the highest
estimated economic risk of corrosion failures. This is approximately 20% of
the total length of large-diameter (>16%) pipelines in our system.

Stress corrosion cracking (SCC) projects

Most of the projects related to SCC have been aimed at gathering data to
more accurately assess the probability of SCC occurring. Expenditure on
these projects account for 16% of total programme costs in the years 1988 to
1990. Projects to excavate specific locations on six pipelines estimated to
have a high risk of SCC occurring were initiated in 1987. One of the pipelines
was found to have SCC, which initiated further projects in 1988 to assess more
locations on that line, which in turn led to a hydrostatic test in 1989. A 1990
project is planned to excavate and examine specific locations on one other

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