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

RISK-BASED INSPECTION METHODOLOGY, PART 2, ANNEX 2.B—DETERMINATION OF CORROSION RATES 2.B-75
2.B.10.7
Figures
Start
Is H 2 0
Present?
Yes
Determine pH
Is
pH > 7?
Yes
Proceed to
Paragraph 2.B.7.
No
No
Estimated Corrosion
Rate is 0
No
Is
pH < 4.5?
Yes
Are Chlorides
Present?
Yes
Proceed to
Paragraph 2.B.2.
No
Material of
construction is
carbon or low
alloy?
No
CR=2mpy
Yes
Determine corrosion
rate CR pH from
Table 2.B.10.2.
• pH
• Temperature °F
Determine adjustment
factor for oxygen From
Table 2.B.10.3.
Oxygen (ppb)
Determine adjustment
factor for velocity F v from
Equations 2.B.2 to 2.B.4.
Velocity (fps)
Calculate Final Corrosion
Rate
CR = CR pH x F o x F v
Estimated
Corrosion Rate
Figure 2.B.10.1—Acid Sour Water—Determination of Corrosion Rate