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

RISK-BASED INSPECTION METHODOLOGY, PART 2—PROBABILITY OF FAILURE METHODOLOGY 2-159
systems, if they were subject to failure by mechanical fatigue, would be expected to fail before reaching
tens or hundreds of million cycles. One should note that intermittent cycles are cumulative.
1) Shaking less than 2 weeks— F fB
AS = 1.
2) Shaking between 2 and 13 weeks— F fB
AS = 0.2.
3) Shaking between 13 and 52 weeks— F fB
AS = 0.02.
d) STEP 4—Determine the type of cyclic loading connected directly or indirectly within approximately
15.24 m (50 ft) of the pipe, and determine the base DF,
CF
D fB
, based on the following criteria.
1) Reciprocating machinery— D CF
fB
= 50.
2) PRV chatter— D CF
fB
= 25.
3) Valve with high pressure drop— D CF
fB
= 10.
4) None— D CF
fB
= 1.
e) STEP 5—Determine the base DF using Equation (2.76).
( )
DfB
= max ⎡
⎢
D , D ⋅ F ,D
⎣
mfat PF AS AS CF
fB fB fB fB
⎤
⎥⎦
(2.76)
f) STEP 6—Determine the final value of the DF using Equation (2.77).
D mfat mfat
f = D fb ⋅ F CA ⋅ F PC ⋅ F CP ⋅ F JB ⋅ F BD
(2.77)
The adjustment factors are determined as follows.
1) Adjustment for Corrective Action, F CA —Established based on the following criteria.
— Modification based on complete engineering analysis—F CA = 0.002.
— Modification based on experience—F CA = 0.2.
— No modifications—F CA = 2.
2) Adjustment for Pipe Complexity, F PC —Established based on the following criteria.
— 0 to 5 total pipe fittings—F PC = 0.5.
— 6 to 10 total pipe fittings—F PC = 1.
— Greater than 10 total pipe fittings—F PC = 2.
3) Adjustment for Condition of Pipe, F CP —Established based on the following criteria.
— Missing or damaged supports, improper support—F CP = 2.