Hi all,
I'm currently working on the design of a Power Plant's main steam line. During normal operation temperature is 485°C @ 66 barg while the design conditions are 510°C @ 79 barg. I'd like to know how does the yield strength of the material changes with the different temperatures. I know that for EN 13480 you can select the amount of ours to be considered for creep. However, I can't seem to find this for the B31.1 Code.
Obviously the design conditions for Temperature comes for a particular situation where the steam temperature goes up (510°C is the Temperature Switch for the Boiler). However, from experience I know that this won't be a common situation (Less than 80hrs a Year) so designing for the sustained design condition doens't seem realistic.
I've been reading the Code and it says that you should design the pipe for the nominal condition + a little margin determined by the manufacturer of the boiler (hence the 485 + 25°C) but given that the pipe will rarely ever see this condition I don't consider I should be taking into acount creep for 510°C.
To sum up: I'd like to know how AutoPipe calculates creep stress (for B31.1) and whether I should design for the nominal or design conditions.
Thanks.
This sounds like an Appendix V application under B31.3, but I don't think B31.1 has such provisions. Not sure if this forum is the best place to ask. Perhaps eng-tips.com may provide more technical advice, surely this question has been addressed there before.
Whether you "should design for the nominal or design conditions" is up to you as the designer, basing this decision on Code requirements.
Greetings,
To know how AutoPipe Calculates Creep stress please refer the Creep analysis with AutoPIPE.