NozzlePRO SPL & SPS calculation at the creep temperature ranges

[fraccionadora]

I cannot verify NozzlePRO calculated SPL & SPS stress limits at the creep temperature ranges.

At the creep temperature ranges [where value of S is governed by time-dependent properties], NozzlePRO takes yield strength into account for the calculation of SPL and SPS stress limits.
However, yield strength shall not be taken into account according to the,
Clause Step 5 (b) of Para 5.2.2.2 of ASME S8D2:2019
Clause (d) of Para 5.5.6.1 of ASME S8D2:2019

To better illustrate the subject, I am sharing the SPL & SPS values for SA 516 Gr70 material @454°C [for which creep temperature is 400°C and above & min. specified yield strength to tensile strength ratio does not exceed 0.7]
If my evaluation is not wrong, for that example
• NozzlePRO calculates SPL as 170 MPa (correct value is 96.75MPa)
• NozzlePRO calculates SPS as 432 MPa (correct value is 303.75MPa).
[P.S: I am using PRG2018, NozzlePRO v12.0]

Sc, cold allowable stress= 138 MPa
Syc, cold yield strength= 262 MPa
Sh, hot allowable stress= 64.5 MPa
Syh, hot yield strength= 170 MPa

SPL to be calculated per Div2 Part5= 96.75 MPa, where SPL=1.5*Sh
SPL calculated by NozzlePro= 170 MPa, where SPL=max(1.5*Sh, Syh)

SPS to be calculated per Div2 Part5= 303.75 MPa, where SPS=3*(Sc+Sh)/2
SPS calculated by NozzlePro= 432 MPa, where SPS=max[3*(Sc+Sh)/2, (Syh+Syc)]

Looking forward to your comments.

 

[Morcuse]

Div 2 Part 5 currently offers no guidance over how to deal with creep. Significant knowledge is required, though there is a codecase relatively new that offers some information.

 

[fraccionadora]

Thank you for your answer Morcuse. API 578 FFS investigates and provide guidance for detailed creep analysis, and creep life analysis and creep-fatigue interaction.
However,still Table 1A allowables are obtained considering creep failure at creep temperature range and refers certain creep life according to allowable stress basis. However, yield strengths in Table Y are not. I interprete that is the reason not to use yield strengths at the creep range for the calculation of SPL and SPS stress limits.