Page 323 - Pipelines and Risers

296 Chapter 16

Incident Frequency Hazard Distance
Dropped Container 5.15 x per hour 15m
Sinking Vessel 2.1 1 x 1u7 pet hour 15Om

Random Failures
Material and corrosion defect failure rates have been taken from PARLOC. Once again this
data is considered to be conservative, particularly with respect to corrosion failure rates for
export gas pipelines with a diameter > 10”. It should, however, be understood that the
corrosion defect failure rates used here can only be considered to be conservative provided
that the pipeline is operated under the design conditions (Le. dry). If the pipeline is to be
frequently or continuously operated under wet conditions then the corrosion related failure
rates would be significantly higher. The failure rates obtained from PARLOC are appropriate
for the localized spot corrosion which may be experienced (often in association with a pre-
existing defect) in a normally dry gas line in which corrosion is actively controlled and
monitored on an ongoing basis.

Cause and Consequence Analysis
The total number of trawler crossings of the pipeline per year has been determined.

It has been assumed that 50% of the trawlers will have a crew of 5 persons and 50% will have
crews of 10 persons.

It has been assumed that 15 people will on average be at risk per merchant vessel. This value
is based on a population at risk of 10 people for 95% of vessels and 100 people for 5% of
vessels.

In the absence of knowledge concerning the intensity of future 3d Party construction activity
it is not possible to predict the Societal Risks that will be associated with those activities.
These risks will be subject to control by the 3Td Party concerned, and will contribute to the
individual risks (the FAR) for those specific activities

In the absence of detailed information concerning the density of merchant vessel shipping, it
has been assumed to be high. A merchant vessel crossing frequency of 29 per km year has
been assumed.