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Quantitative risk assessment of the performance of barriers controlling fire and explosion risk

Govindarajan, Saikrishna
Master thesis
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URI
https://hdl.handle.net/11250/2656760
Date
2019
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  • Institutt for marin teknikk [2405]
Abstract
The growing population of the world places an enormous demand for energy in some

form or the other. Essentially, this means that the struggle to hunt and retrieve fossil fuels

has to continue for the smooth functioning of the world. Since the early 1900’s when drilling

for oil and gas started moving away from shores to some remote locations that we are at

today, the size and complexity of machinery and the interconnected systems have grown

exponentially. Despite investing enormous time, effort and money into implementing technically

advanced and innovative barrier systems to prevent Hydrocarbon (HC) leaks on

offshore installations in the Norwegian Continental Shelf (NCS), the statistics still stands

far from the target zero. Hence, the efforts towards minimizing the number of leaks can

never be ceased due to the catastrophic nature of its potential consequences to humans,

environment, asset or the reputation of a firm.

This master’s thesis features one such effort to visualize the effectiveness of some

barrier functions proposed in Modelling Instantaneous Risk for Major Accident Prevention

(MIRMAP) report. Some of the most critical barrier systems are incorporated into

the chosen generic module, which is then subjected to numerous gas leak simulations using

the latest version of the software, Kameleon FireEx - Risk and Barrier Management

(KFX-RBM), a Computational Fluid Dynamics (CFD) based simulation tool. A base case

scenario is a set-up using the chosen module with a 100% functional gas detection system,

Emergency Shutdown (ESD) system, with no temporary weather cladding attached and

closed fire-proof doors. This set-up is subjected to simulation with six different leak rates,

four different wind speeds and two different wind directions. The results of this being a

base for comparison, simulations are carried out with partially isolated gas detection system,

presuming on-going hot works in the near vicinity with a temporary weather cladding

and with fireproof doors left in open position. The variations in the total ignition probability

of the module compared to the base case would be the main objective of this thesis.

As additional objectives, since the barrier systems could be directly or indirectly influenced

by humans, an attempt is made by simulating the base case with a practically

acceptable delay in manual activation of the shutdown. Furthermore, to reduce the simulation

time, numerous simulations are run to arrive at the optimal grid resolution and courant

number with the quality of results remaining undiminished.

The case with delayed shutdown due to manual activation of ESD depicted the highest

influence to the complementary cumulative frequencies, followed by the case simulated

with a temporary weather cladding erected on one of the open ends of the module, with

second highest influence. The comparison of the two base case simulations with different

leak scenarios (direction and location), revealed that the release point and release direction

can significantly influence the probabilities of ignition, either positively or negatively. The

simulations that were carried out to optimize the grid resolution resulted in a significant

reduction of simulation time with a grid resolution of 125000, while the quality of the results

was undiminished. Further analysis by extracting the highest and the least release

rates separately resulted in an insight that the grid resolution is a function of release rate.
Publisher
NTNU

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