Page 316 - Pipelines and Risers

Risk Analysis applied to Subsea Pipeline Engineering 289

Discharge
In order to determine dispersion, information is required for the discharge, this includes; hole
size, duration, rate and quantity.

Dispersion of Gas
Leakage of a gas pipeline under water will result in a plume, which rises and exits from the
surface of the water in the shape of a circle.

?l
dl
Combustion

Damage
and

Figure 16.4 Modeling of Consequence.

Dispersion of Liquid
The dispersion is dependent on the fluid released. Unstable condensate tends to be modeled as
gas release (though a sound qualitative discussion about hydrate formation in water is
required). Stable condensates will eventually rise to the surface to form a liquid pool at the
surface. However, much of the dispersion is very complex and difficult to model.

Ignition
A leakage which does not ignite (Le. not toxic, H2S) will not present a risk to humans. A risk
of ignition is developed using the following equation:
ffiefiakage x Pignition (per year) (16.2)

pignition is probability of ignition occurring, given a leak of a flammable substance. This can be
determined using an ignition model, which considers all possible methods by which ignition
could take place.

Subsea releases can usually be considered to be delayed hence, ignition will result in an
explosion or flash fire (few unconfined flammable gas clouds will develop into an explosion)
for gas leakage. Fire pool could arise from an oil leak. However, in the case of a shallow