Page 457 - Pipeline Pigging Technology

Pipeline Pigging Technology

DISCUSSION

The risk-assessment methodology that is the basis for our pipeline integrity
programme has resulted in continued focus of our efforts to reduce the risks
of failures caused by external corrosion. The resulting pipeline-integrity
projects involve in-line inspection of pipelines which have very high eco-
nomic consequences of an outage, or very large numbers of known corrosion
damage areas. Both these situations place a premium on the ability of in-line
inspection to provide data that allows failure pressures to be estimated
without excavations to determine the size of corrosion damage.
When excavating locations to investigate external corrosion or stress
corrosion cracking, it is NOVA's policy to reduce the pressure to 70% of the
recent operating pressure to protect the safety of workers. Even with advance
planning, such pressure reductions can affect border deliveries under the
current situation with the system operating so close to capacity throughout
the year. In the case of one project to assess anticipated corrosion on a line
with moderate outage probability but very high outage consequences, such
pressure reductions would have resulted in reduced gas exports valued at
over $ 1 million per day if any other operating disruptions occurred. As a result,
an "advanced" ILI system, whose performance has been established[8], was
used on this line, rather than a lower-cost conventional system, in order to
avoid the excavations that would have been otherwise required to assess the
significance of detected corrosion damage. Even so, the reduction in gas
volumes required for in-line inspection is a disruption to system operation.
We are examining methods of including such business effects in the cost
estimates of pipeline integrity projects, to make sure that the cure (pipeline
integrity project) is not worse that the disease (an unplanned outage due to
a failure). We are also encouraging the vendors of inspection services to
develop methods that will allow their equipment to perform in high-velocity
gas streams, so that we can refer to it as "on-line" inspection, rather than "in-
line", which it truly is at present.

CONCLUSIONS

1. NOVA's pipeline-integrity programme has allowed us to determine what
testing and inspection programmes are appropriate to our system.
2. With a total cost of 2% of operation and maintenance costs, the
programme is affordable.

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