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in the field of prediction to build simulation models
Fig. 4 - Bath tub curve when maintenance and operations records are not
available. Reliability can then be represented by eq.
2 (Smith, 1997 [7]).
R = e –λt (3)
where
R is the reliability
λ is the failure rate and t represents time
Criticality
Systems and equipment are categorised as either
‘”critical” or “non-critical” in terms of their impact on systems:
production. Failure of critical equipment results in
the loss of normal production associated with that
item. Conversely, failure of non-critical equipment
has no impact on production. For instance, a
parallel configuration can be described with a term
such as “2 × 100%”.
2 × 100% critical units do not cause production
losses unless both items have failed and are failed
simultaneously (i.e. redundancy (Lamberson and
Kapur, 1977 [10])). Conversely, failure of either
one of 2 × 80% critical units will cause normal
production to reduce to 80%.
Fig. 5 - Full Supply Chain Monte Carlo simulation
Production Availability There exists a number of numerical methods used
Diagram (PAD)
(e.g. Markov, Petri Net etc.), but the Monte Carlo
modeling technique is the most widely used for the
simulation of complex and dynamic interactions
(MIL-HDBK-338B, 1998 [1]). A random number
generator is used to provide a probability of a
failure occurring which in turn is used to calculate
the time to the next failure. The Monte Carlo
model can be used to model any failure pattern
or repair characteristic for which data is available.
The outputs are a time-based availability curve
for the length of the simulation. The availability of,
and contribution to the overall downtime of each
branch, sub-system or individual equipment item
can be illustrated.
Case study:
FLNG ram analysis
The FLNG project & project
objectives
A Full Supply Chain (FSC) RAM analysis has been
performed by Bureau Veritas on the concept stage
of a FLNG project. The FLNG project consists of
an offshore floating facility able to treat and liquefy
feed gas from subsea wells, and store and offload
LNG onto LNG carriers as presented in figure 5.
The subsea is composed of two different types of
• subsea facilities systems which are mainly
composed of items directly linked to the gas
production from wells (i.e. Wellheads, X-mas
trees, Manifolds, Flow lines, Risers);
• subsea control and safety systems which are
mainly composed by items linked to the control
of subsea equipment and safety functions.
FLNG has been designed to produce about 3 mtpa
of LNG. The FLNG facilities modelled include:
• production turret swivel assembly;
• raw gas treatment systems;
• gas dehydration systems;
• condensate recovery systems;
• liquefaction of dry gas;
• utility systems (power generation, fuel gas and
Impiantistica Italiana - Maggio-Giugno 2015 93