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

RISK-BASED INSPECTION METHODOLOGY, PART 2—PROBABILITY OF FAILURE METHODOLOGY 2-125
1. If the coating has failed at the time of inspection when age tke was established, then
Coat adj = 0
2. If the coating has not failed at the time of inspection when age tke was established, use Equation
(2.36) to calculate Coat adj
( ) ( )
Coat min C ,age min C ,age age
adj = age coat − age coat − tke
(2.67)
g) STEP 7—Determine the in-service time, age, over which external CUI ClSCC may have occurred using
Equation (2.68).
age age Coat
= crack − adj
(2.68)
h) STEP 8—Determine the number of inspections performed with no cracking detected or cracking was
repaired and the corresponding inspection effectiveness category using Section 18.6.2 for past
inspections performed during the in-service time. Combine the inspections to the highest effectiveness
performed using Section 3.4.3. Cracking detected but not repaired should be evaluated and future
inspection recommendations based upon FFS evaluation.
i) STEP 9—Determine the base DF for CUI ClSCC,
CUI − ClSCC
D fB
, using Table 6.3 based on the number of
inspections and the highest inspection effectiveness determined in STEP 8 and the Severity Index, S VI ,
from STEP 2.
j) STEP 10—Calculate the escalation in the DF based on the time in service since the last inspection
using the age from STEP 7 and Equation (2.69). 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.
CUI −ClSCC
11 .
( fB ( ) )
CUI −ClSCC
D f = min D ⋅ max[ age, 1. 0] , 5000 (2.69)
18.7 Nomenclature
age
age coat
age crack
C age
Coat adj
is the component in-service time since the last cracking inspection or service start date
is the in-service time since the coating installation
is the in-service time since the last ClSCC inspection
is the total anticipated coating life from the time of installation
is the coating adjustment
CUI − ClSCC
D f
is the DF for CUI ClSCC
CUI − ClSCC
D fB
is the base value of the DF for CUI ClSCC
S VI
is the Severity Index