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

2-146 API RECOMMENDED PRACTICE 581
3) Determined by chemical composition correlations. Use the chemical composition to determine the
J-factor or X-bar factor using Equation (2.71) and Equation (2.72). The J-factor and X-bar factor
may be correlated to the expected ∆FATT after long-term service. Based on long-term exposures,
this is conservatively correlated to the J-factor and X-bar factor in Equation (2.74) and Equation
(2.75), respectively.
4 2
FATT 77. 321 (0. 57570 J-factor) (5.
5147 (10 ) (J-factor ))
∆ = − + ⋅ − ⋅ × (2.74)
2
FATT 87. 335 (11. 437 X-bar) (01472 . (X-bar ))
∆ = − + ⋅ − ⋅ (2.75)
4) Determined by using conservative assumptions based on year of fabrication. A conservative value
of can be assumed for the long term ∆FATT depending on the year of fabrication as follows:
— fourth generation equipment (after to 1988): 66 °C (150 °F);
— third generation equipment (1981 to 1987): 121 °C (250 °F);
— second generation equipment (1973 to 1980): 149 °C (300 °F);
— first generation equipment (1965 to 1972): 177 °C (350 °F).
e) STEP 5—Calculate T ref + ∆FATT using T ref from STEP 3 and ∆FATT from STEP 4.
f) STEP 6—Calculate the DF,
tempe
D f
condition and where T ref + ∆FATT is from STEP 5.
, using Table 20.4 or Table 20.5 based on the component PWHT
NOTE
Use T MPT – (T ref + ∆FATT) in place of CET − T ref with T MPT from STEP 1 or STEP 2, as applicable.
21.7 Nomenclature
age
is the in-service operating time, hours
tempe
D f
is the DF for low alloy steel embrittlement
SCE
T MDT
T MPT
T ref
YS
∆FATT
is the specified change in FATT
is the minimum design temperature, °C (°F)
is the minimum pressurization temperature, °C (°F)
is the reference temperature, °C (°F)
is the material yield strength
is the change in the fracture appearance transition temperature, °C for equations in this
section
21.8 References
See References [76], [84], [85], [86], [87], [88], [89], and [90] in Section 2.2.