ASME VIII-2 2025-temperature gap covered between fatigue and creep-fatigue

[YuJie_PV]

hi all,

I am reading the newly added provisions "5.6.4 PROTECTION AGAINST FAILURE FROM CREEP FATIGUE" in 2025 edition of ASME VIII-2, i find there is a gap of temperature between those covered by "5.5 Protection Against Failure From Cyclic Loading", and para.5.6.4.
para. 5.6.4.1 indicates "For load cycles occurring completely within the low-temperature, time-independent regime, the provisions of 5.5 still apply." but S-N curve in annex 3-F only allow a temperature which may be lower than when creep governs the allowable stress, for many materials. for instance, S-N curve of 304 is applicable when not exceeding 427°C (800°F), while the temperature limit used to define the Creep Range is 510C.
TGS4 ever replied in a thread that "Above that temperature, you are into creep-fatigue. Creep-fatigue starts at a temperature lower than when creep governs the allowable stress."
i am confused again. is there a temperature gap between para.5.5 and para.5.6.4? am i missing something?

Thanks so much.

 

[TGS4]

You're not missing anything.

From the Foreword:
"The Code is not a handbook and cannot replace education, experience, and the use of engineering judgement."

 

[YuJie_PV]

@TGS4，thanks for the clarification.
as para. 5.6.4.1 indicates "For load cycles occurring completely within the low-temperature, time-independent regime, the provisions of 5.5 still apply." , and para.5.5 directs engineers to the curves in annex 3-F， may i take it as that the code intends the S-N curves in annex 3-F are applicable to the situation as mentioned above?

Thanks in advance.

 

[TGS4]

I wouldn't make that leap. The temperature limits in the fatigue curves still need to be obeyed.