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-117
Table 2.B.14.14—Product-Side Water Draw-off Adjustment
Water Draw-off
Multiplying Factor—F WD
2.B.14.6
Figures
Soil Side
No 1.0
Yes 0.7
Product Side
• Average time to
leakage
• Thickness
• “Default” = 5 mpy
Establish Base Corrosion
Rate for Soil Side Corrosion
Establish Base Corrosion
Rate for Internal
Bottom Corrosion
• Inspection Data
• BS&W
• pH
Resistivity
Determine Adjustment factor
for Soil Conditions
Tank Pad Type
Determine Adjustment factor
for Tank Pad Material
Determine Adjustment factor
for Product Conditions
Product Conditions
Water Drainage
Determine Adjustment factor
for Drainage
Determine Adjustment factor
for Operating Temperature
Bulk Fluid
Temperature
Cathodic Protection
Determine Adjustment factor
for Cathodic Protection
Determine Adjustment factor
for Steam Coil Heater
Use of Steam Coil
Heater
Bottom Design
Determine Adjustment factor
for Bottom Type
Determine Adjustment factor
for Water Draws
Water Draw
Bulk Fluid
Temperature
Determine Adjustment factor
for Operating Temperature
Calculate Modified Soil Side
Corrosion Rate
(Always Localized)
Calculate Modified
Product Side
Corrosion Rate
(Widespread or Localized)
Product Side CR
Widespread
Is
Product Side
Bottom Corrosion
Widespread or
Localized
Product Side CR
Localized
Sum Corrosion Rates
Use the Greater
Of Corrosion Rates
Final Estimated
Corrosion Rate
Figure 2.B.14.1—AST Bottom Corrosion—Determination of Soil-Side and Product-Side Corrosion Rates