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cost of deferred production.

The expected (average) number of loss of containment incidents, associated fatalities and
environmental damage can be used to derive an expected cost incorporating each of the
quantities given above. A detailed methodology by which to evaluate financial risk has been
developed in the paper by Bai et al. (1999) and can also be used to minimize these potential
costs to the owner of the pipeline

16.8 Example 1: Risk analysis for a Subsea Gas Pipeline

16.8.1 General
This risk analysis example will evaluate the risk acceptance and risk estimation of a North Sea
pipeline transporting dry gas.

This example will cover all aspects of the risk methodology developed in the chapter. By
firstly determining the gas release for different hole sizes it is then possible to determine the
potential effects on each type of risk.
16.8.2 Gas Releases
In order to provide an analysis that can be considered representative for the entire pipeline,
the release rates have been estimated (conservatively) on the assumption that the water depth
is 300m. This leads to a differential pressure at the site of loss of containment of = 250 bar.

Representative Hole Sizes
Potential hole sizes will be modeled through the use of three representative hole sizes with
diameters of 20mm, SOmm, and 200mm. The 20mm and 8Omm hole sizes have been selected
to provide ease of comparison with the hole sizes considered in the PARLOC database. The
largest hole size considered is 200mm. This is considered to be a conservative upper bound to
the equivalent hole size caused by major structural damage to the pipeline.

Discharge
Release rates have been estimated using SPILL. This is part of the HGSystem suite of
programmer. The rates predicted for these hole sizes are given below. Indicative duration’s
for these releases are also shown below. These durations are based on the time required to
blow down the pipeline through the hole and it is assumed that the mass release rates decrease
linearly with time.

20mm hole 14.6 kg/sec 6000 hours
8Omm hole 233.2 kg/sec 375 hours
200mm hole 1457.1 kg/sec 60 hours