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

RISK-BASED INSPECTION METHODOLOGY, PART 2—PROBABILITY OF FAILURE METHODOLOGY 2-91
d) STEP 4—Determine the number of inspections and the corresponding inspection effectiveness category
using Section 14.6.2 for past inspections performed during the in-service time. Combine the inspections
to the highest effectiveness performed using Section 3.4.3.
e) STEP 5—Determine the base DF for HIC/SOHIC-HF,
HIC / SOHIC−
HF
D fB
, using Table 6.3 based on the
number of inspections and the highest inspection effectiveness determined in STEP 4 and the Severity
Index, S VI , from STEP 2.
f) STEP 6—Determine the on-line adjustment factor, F OM , from Table 14.4.
g) STEP 7—Calculate the final DF accounting for escalation based on the time in service since the last
inspection using the age from STEP 3 and Equation (2.31). In this equation, it is assumed that the
probability for cracking will increase with time since the last inspection as a result of increased exposure
to upset conditions and other non-normal conditions. The equation also applies the adjustment factor for
on-line monitoring.
( max[ 1 0] ) 11 .
⎛ HIC / SOHIC−HF
D
HIC / SOHIC HF
fB
⋅ age, . ⎞
−
D f
= min⎜
, 5000⎟
⎜
F
⎝
OM
⎟
⎠
(2.31)
14.7 Nomenclature
age
is the component in-service time since the last cracking inspection or service start date
HIC / SOHIC HF
D f
−
is the DF for HIC/SOHIC-HF
HIC / SOHIC HF
D fB
−
is the base value of the DF for HIC/SOHIC-HF
F OM
S VI
is the on-line monitoring adjustment factor
is the Severity Index
14.8 References
See References [10], [81], and [82] in Section 2.2.