Page 318 - Pipelines and Risers

Risk Analysis applied to Subsea Pipeline Engineering 29 1

Uncertainty
All of the models in the sequence of analysis contain a significant degree of uncertainty. If
taking a pessimistic approach and use factors of safety in the magnitude of 1.5 for each stage
of calculation this will result in a total factor of safety of (1.54=) 5. This might be an
unrealistic overestimate of the total value so it is necessary to adjust this figure to suit the
situation.

Another difficulty with the consequence Modeling technique is that it is necessary to assume
an initial discharge condition (i.e. the size of hole). This has a large influence over the models
used, for a more comprehensive analysis a sample of likely release conditions could be
evaluated. However, generalizations can be made regarding hole size based on failure rate
data and type of failure, e.g. corrosion is likely to lead to smalypin pricks, where as third party
interference tends to cause large diameter holes.

16.7.2 lS' Party Individual and Societal Risk
As implied by the definition of each of these risks, the consequences will be measured in
terms of the human life loss as a consequence of an initiating event. The unit used to assess
the loss is the Fatal Accident Rate (FAR), which can be defined as the number of fatalities per
10' hours worked.

16.7.3 Environmental Risks
In determining environmental risk, it is necessary to evaluate the consequences of the loss of
containment, and also the probability of loss of containment. The cause of initiation is the
same as for the initiation of individual and societal risk.

The consequence can be determined in terms of the following factors.

1. The category of fluid
A detrimental consequence will usually only arise from fluid releases (Le. oil).
2. The location of release
A pollution impact assessment will provide an understanding of the sensitivity and
balance of the surrounding ecosystem, such that an assessment can be made of the damage
incurred by contamination of the fluid being transported.
3. The volume and dispersion of release
The volume of release is dependent on both the rate and the duration of the release. The
dispersion of the release will be different for subsea and atmospheric releases. This
analysis can be undertaken using an appropriate computer-Modeling program.

16.7.4 Material Loss Risk
The cost due to any failure incident is an aggregation of the following costs:

notional cost of fatalities and environmental damage;