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

2-124 API RECOMMENDED PRACTICE 581
18.6.3 Calculation of the DF
The following procedure may be used to determine the DF for CUI ClSCC; see Figure 18.1. Note that a high
susceptibility should be used if cracking is known to be present.
a) STEP 1—Determine the susceptibility using Table 18.2 based on the driver and the operating
temperature and the following adjustment factors.
1) Adjustments for Piping Complexity—If the piping complexity is Below Average, then decrease
susceptibility one level (e.g. Medium to Low). If the piping complexity is Above Average, then
increase susceptibility one level (e.g. Medium to High). If the piping complexity is Average, then
there is no change in the susceptibility.
2) Adjustments for Insulation Condition—If the insulation condition is Above Average, then decrease
susceptibility one level (e.g. Medium to Low). If the insulation condition is Below Average, then
increase susceptibility one level (e.g. Medium to High). If the insulation condition is Average, then
there is no change in the susceptibility.
3) Adjustments for Chloride-free Insulation—If the insulation contains chlorides, then there is no
change in the susceptibility. If the insulation is chloride free, then decrease the susceptibility one
level (e.g. Medium to Low).
Note that a high susceptibility should be used if cracking is confirmed to be present.
b) STEP 2—Determine the Severity Index, S VI , using Table 17.3, based on the susceptibility from STEP 1.
c) STEP 3—Determine the in-service time, age crack , since the last Level A, B, or C inspection was
performed with no cracking detected or cracking was repaired. Cracking detected but not repaired
should be evaluated and future inspection recommendations based upon FFS evaluation.
d) STEP 4—Determine the in-service time, age coat , since the coating has been installed using
Equation (2.65).
age = Calculation Date − Coating Installation Date
(2.65)
e) STEP 5—Determine the expected coating age, C age , based on coating type, quality of application and
service conditions. C age should be 0 years for no coating or poorly applied coating. Lower quality
coatings will typically have a C age of 5 years or less. High quality coatings or coatings in less harsh
external environments may have a C age of 15 or more years. C age may be adjusted based on an
evaluation of the coating condition during a high-quality inspection.
f) STEP 6—Determine the coating adjustment, Coat adj , using Equations (2.66) and (2.67).
If agecrack
≥ agecoat:
( )
Coat = min C ,age
adj age coat
(2.66)
If agecrack
< agecoat: