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

RISK-BASED INSPECTION METHODOLOGY, PART 2—PROBABILITY OF FAILURE METHODOLOGY 2-115
Table 16.1—Data Required for Determination of the DF—CUI (Continued)
Required Data
Comments
Pipe support penalty? (Yes/No)
Interface penalty? (Yes/No)
Inspection effectiveness category
Number of inspections
Thickness reading
If piping is supported directly on beams or other such configuration that does not
allow for proper coating maintenance, CUI can be more severe.
If the piping has an interface where it enters either soil or water, this area is subject
to increased corrosion.
The effectiveness category that has been performed on the component.
The number of inspections in each effectiveness category that have been
performed.
The thickness used for the DF calculation is either the furnished thickness or the
measured thickness (see Section 4.5.5).
Thickness reading date
The date at which the thickness measurement used in the calculation was
obtained. If no acceptable inspection has been conducted, the installation date
should be used.
Table 16.2—Corrosion Rates for Calculation of the DF—CUI
Operating
Temperature
(°F)
Corrosion Rate As a Function of Driver 1 (mpy)
Severe Moderate Mild Dry
10 0 0 0 0
18 3 1 0 0
43 10 5 3 1
90 10 5 3 1
160 20 10 5 2
225 10 5 1 1
275 10 2 1 0
325 5 1 0 0
350 0 0 0 0
NOTE 1 Driver is defined as the CUI condition causing the corrosion rate. See Part 2, Section 15.6.2 for
explanation of drivers.
NOTE 2 Interpolation may be used for intermediate values of temperature.