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

2.B-100 API RECOMMENDED PRACTICE 581
2.B.12.6
References
See References [134], [138], [139], [140], [141], [142], [143], and [144] in Section 2.2.
2.B.12.7
Tables
Table 2.B.12.1—Soil-Side Corrosion—Basic Data Required for Analysis
Basic Data
Base corrosion rate,
mm/yr (mpy)
Equipment temperature,
°C (°F)
Soil resistivity, Ω-cm
Cathodic protection
(CP)
Coating
Equipment age, years
Comments
The expected or observed corrosion rate for
the buried structure, or a “similar” structure
under “similar” service and conditions.
Equipment temperature (operating
temperature for piping and pipelines).
Soil characteristics in the vicinity of the
buried structure.
Specify whether or not a CP system is
installed and how effective it is.
Type of coating, age, temperature abuse,
and inspection and maintenance history, if a
coating is installed.
The time since installation of the buried
equipment—used to determine accumulated
corrosion over time since buried.
Table 2.B.12.2—Base Corrosion Rate
Factors Affecting Base Corrosion Rate
Base Corrosion
Rate
Primary Soil
Type
Sand
Level of Chemical
Contaminants
Low chlorides
(inland, non-industrial)
Particle Size and Uniformity Moisture Level mm/y mpy
Homogeneous, fine silt or sand Dry, desert-like 0.03 1
Silt Moderate (industrial) Mixed Variable moisture 0.13 5
Clay
High chlorides
(coastal areas)
>50 % gravel Normally saturated 0.25 10
Table 2.B.12.3—Soil Resistivity Adjustment
Resistivity (Ω-cm) Corrosiveness Multiplying Factor
<500 Very Corrosive 1.50
500 to 1,000 Corrosive 1.25
1,000 to 2,000 Moderately Corrosive 1.00
2,000 to 10,000 Mildly Corrosive 0.83
>10,000 Progressively Less Corrosive 0.60
Table 2.B.12.4—Equipment Temperature Adjustment