Environmental Engineering Reference
In-Depth Information
PSA model: level 1, internal IS, external
IS, fires, earthquakes, etc
Parameter of the PSA model:
- The component is not ready as a result
of independent failure, repair and TM, for
general reasons;
Reliability model:
Q
(
t
) =
f
(failure type, age, strategies)
Data available for reliability:
- Service experience (failures, loading in
service, environmental factors...);
- Service documentation (tests and TM);
- Results of reliability tests (accelerated
ageing)
Calculation of parameters
- Parameters of reliability model
- Not ready
2.10
Selecting a model of reliability for use in PSA.
It should be noted that the linear model and the Weibull distribution
are special cases of generalised linear models and can be used both for
modelling failure in operation or standby mode (continuous distribution)
and for failure on demand (discrete distribution).
Unavailability of the element at a specified time interval (an input
parameter PSA models) can be expressed in the following form:
∫
q t q
( ) =
+ 1
−
exp
−l
( ')
t dt
' ,
[2.14]
0
Here
q
0
is the value of unavailability of equipment at time
t
= 0.
Wesley
25
proposes to calculate the unavailability of recoverable items
following analytical relations obtained for the linear model:
1
qt
( ) = 1
−
exp
2(
−
[2.15]
2
at t
−
)
N
for full recovery (as good as new) as a result of repair or technical
maintenance (TM)
1
qt
( ) = 1
−
exp
2(
−
[2.16]
2
2
at t
−
)
N
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