API RP 581 - 3rd Ed.2016 - Add.2-2020 - Risk-Based Inspection Methodology

5-38 API RECOMMENDED PRACTICE 581
D is the probability adjustment for t
rate1
Bundle
1
D is the probability adjustment for t
rate2
Bundle
2
D is the probability adjustment for t
rate3
Bundle
3
EIR is the expected incremental risk between turnaround dates T1 and T2, $/year
ERL
t 2
t1
ESL
n
is the estimated remaining life of the bundle, years
is the estimated service life of a bundle as a function of replacement time interval, years
ESL is the average life of bundles that would have failed at the replacement time interval, years
f , n
ESLf , n − 1
is the average life of bundles that would have failed at the previous replacement time interval
(n-1), years
ESL
pn ,
is the average life of bundles that would not have failed at the replacement time interval, years
LEF is the bundle life extension factor
matcost is the material cost factor for the tube bundle material of construction
MTTF is the mean time to failure, years
N
is the number of bundles in a heat exchangers past history
Outage
mult
is the outage multiplier factor of the unit
tube
P
f
is the probability of the bundle failure, failures/year
tube
P
f , n
is the probability of bundle failure calculated for the current (n) increment of the optimization
procedure, failures/year
tube
Pf , n − 1
is the probability of bundle failure calculated for the previous (n-1) increment of the
optimization procedure, failures/year
tube
P f , w / insp
is the probability of bundle failure at the plan date with inspection, failures/year
tube
P
f , tgt
is the maximum acceptable probability of bundle failure based on the owner-user’s risk target,
failures/year
PBL is the predicted bundle life adjusted based on inspection, years
adj
r
is the number of failed bundles in a heat exchangers past history
R( t )
is the risk as a function of time, m 2 /year (ft 2 /year) or $/year