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-115
Table 2.B.14.4—Soil-Side Soil Resistivity Adjustment Factor
Resistivity (ohm-cm) Potential Corrosion Activity Multiplying Factor—F SR
<500 Very corrosive 1.5
500 to 1,000 corrosive 1.25
1,000 to 2,000 Moderately corrosive 1.0
2,000 to 10,000 Mildly corrosive 0.83
>10,000 Progressively less corrosive 0.66
AST with RPB 1.0
Table 2.B.14.5—Soil-Side AST Pad Adjustment Factor
AST Pad Type
Multiplying Factor—F PA
Soil with high salt 1.5
Crushed limestone 1.4
Native soil 1.3
Construction grade sand 1.15
Continuous asphalt 1.0
Continuous concrete 1.0
Oil sand 0.7
High resistivity low chloride sand 0.7
Table 2.B.14.6—Soil-Side AST Drainage Adjustment Factor
AST Drainage Type
Multiplying Factor—F TD
One-third frequently underwater 3
Storm water collects at AST base 2
Storm water does not collect at AST base 1
Table 2.B.14.7—Soil-Side CP Adjustment Factor
CP Type
Multiplying Factor—F CP
None 1.0
Yes not per API 651 0.66
Yes per API 651 0.33
Table 2.B.14.8—Soil-Side AST Bottom Type Adjustment
AST Pad Type
Multiplying Factor—F TB
RPB not per API 650 1.4
RPB per API 650 1.0
Single bottom 1.0