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

2-64 API RECOMMENDED PRACTICE 581
Table 9.2—Environmental Severity—HIC/SOHIC-H 2 S Cracking
pH of Water
Environmental Severity as a Function of H 2 S Content of Water
<50 ppm 50 to 1,000 ppm 1,000 to 10,000 ppm >10,000 ppm
a
<5.5 Low Moderate High High
5.5 to 7.5 Low Low Low Moderate
7.6 to 8.3 Low Moderate Moderate Moderate
8.4 to 8.9 Low Moderate Moderate a High a
>9.0 Low Moderate High a High a
If cyanides are present, increase the susceptibility to HIC/SOHIC-H 2 S one category for pH > 8.3 and H 2 S concentrations
greater than 1,000 ppm.
Table 9.3—Susceptibility to Cracking—HIC/SOHIC-H 2 S
Susceptibility to Cracking as a Function of Steel Sulfur Content
Environmental
Severity
High Sulfur Steel a
>0.01 % S
Low Sulfur Steel
≤0.01 % S
Product Form—
Seamless/Extruded Pipe
As-welded PWHT As-welded PWHT As-welded PWHT
High High High High Medium Medium Low
Moderate High Medium Medium Low Low Low
Low Medium Low Low Low Low Low
a Typically includes A70, A201, A212, A285, A515, and most A516 before about 1990.
Table 9.4—Determination of Severity Index—HIC/SOHIC-H 2 S Cracking
Susceptibility
Severity Index—S VI
High 100
Medium 10
Low 1
None 0
Table 9.5—On-line Monitoring Adjustment Factors for HIC/SOHIC-H 2 S
On-line Monitoring Method
Adjustment Factors as a Function of
On-line Monitoring—F OM
Key process variables 2
Hydrogen probes 2
Key process variables and hydrogen probes 4
NOTE The adjustment factors shown above are estimates providing a measure of the relative
effectiveness of various on-line monitoring methods. Factors based on the user’s experience can be
used as a substitute for the values presented in this table.