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-89
Table 2.B.11.4—CR B Base Corrosion Rate Calculation
Chloride Content (ppm)
RSI > 6 or Velocity > 8 ft/s
Base Corrosion Rate, CR B (mpy)
RSI ≤ 6 and Velocity ≤ 8 ft/s
5 1 0.3
10 2 0.6
50 4 1.4
100 6 2
250 9 3
500 13 4.3
750 15 5
1,000 17 5.7
2,000 17 5.6
3,000 16 5.4
5,000 15 4.9
10,000 13 4.3
NOTES
— RSI < 4—Heavy scale forming, non-aggressive.
— RSI 5 to 6—Slightly scale forming and mildly aggressive.
— RSI 6 to 6.5—Balanced or at CaCO 3 saturation.
— RSI 6.5 to 7—Non-scaling and slightly aggressive.
— RSI > 8—Under-saturated, very aggressive.
Table 2.B.11.4M—CR B Base Corrosion Rate Calculation
Chloride Content (ppm)
RSI > 6 and Velocity > 2.4 m/s
Base Corrosion Rate, CR B (mm/y)
RSI > 6 and Velocity ≤ 2.4 m/s
5 0.03 0.01
10 0.05 0.02
50 0.1 0.04
100 0.15 0.05
250 0.23 0.08
500 0.33 0.11
750 0.38 0.13
1,000 0.43 0.14
2,000 0.43 0.14
3,000 0.41 0.14
5,000 0.38 0.12
10,000 0.33 0.11
NOTES
— RSI < 4—Heavy scale forming, non-aggressive.
— RSI 5 to 6—Slightly scale forming and mildly aggressive.
— RSI 6 to 6.5—Balanced or at CaCO 3 saturation.
— RSI 6.5 to 7—Non-scaling and slightly aggressive.
— RSI > 8—Under-saturated, very aggressive.