B31.3 Appendix P

Dear All,

to avoid extra runs in case of lift off supports, we want to use B31.3 Appendix P in Caesar. As I understand, there must be determined a operating stress So and the operating stress range SE? Is it still possible to use load cases as shown below or there are any special requirements to get valid results?

L1: P1+W+T1 (OPE)
L2: P1+W (SUS)
L3: L1-L2 (EXP)


thanks

Those load cases are appropriate.
You can throw a switch in your configuration file to apply Appendix P. This will add an allowable stress limit to the operating stress report.
Based on your load case example, you will now check stresses in L1, L2 and L3.

Dave,

My opinion is that those load cases are appropriate for a system with no lift off supports. For lift-off supports is still valid the old way (i.e. remove the lift-off support on a separate file), since we still have to check the sustained stress in all states.

Please let me know if you agree.

Best regards,

Apendix P states:

"Replace para. 302.3.5(d) with the following...........(d) Allowable Operating Stress Limit"

para. 302.3.5(c) (c) Longitudinal Stresses, SL. is still valid.

With no lift off, there is little reason to go to Appx. P. Appx. P eliminates the problem of defining SL in the equation for SA - the allowed limit for expansion stress range. You may have this problem in liftoff situations - what SL do you use?

So:
If linear, check sustained and expansion.

If nonlinear, either
1) check sus & exp then remove the liftoff supports and check sus again
2) activate Appx. P and check ope, sus & exp
3) use f*(1.25*Sc+.25Sh) as SA and check sus & exp
4) check exp & sus and "fake" a "hot sustained" evaluation by running (operating)-(Tn+Dn) as a sustained case.
5) ignore it except for "large" liftoff and check sus & exp

I think 5) works fine. If there is a small(?) "collapse" associated with the liftoff, the pipe deflection is limited by this liftoff gap. This, by definition, is a displacement-based or stress-limited load and evaluated as an expansion stress range component. This is what C2 has been doing all along. We do not ignore the liftoff, we put it with the expansion evaluation.

SEE CORRECTION BELOW.

Dave,

This is an interesting topic and I like to go further, even if I risk my chances to be hired by you.

My opinion is that with the 302.3.5(d), in case of lift-off, since the W+P was lower than the real one, lead to a conservative EXP. Problem was solved in this way by Appendix P. But still within the ope allowable you can not determine the real SUS since you have the load case W+P (with all supports active). Para. 302.3.5(c) being still valid, the lift-off need to be investigated old fashion way.

If you consider lift-off expansion issue and not sustained issue this is another discussion. Some think it is, some don't.

For 4) this is valid for linear system and not for nonlinear.

Best regards,

Dan,

I was typing faster than I was thinking. Thank you for your correction.

This may help.

Appendix P was established to address uncertainty in the value used for SL in B31.3 equation (1b). Appendix P is an alternative to evaluating the expansion stress range. Appendix P has no effect on the requirements to satisfy the requirements for longitudinal stress (SL) due to sustained loads.

In nonlinear situations, SL may change. For SL, you may want to check this stress in all support configurations.

I claim that running an (operating case) minus (all expansion effects) will give SL in nonlinear cases as well.

Dave,

Thank you very much, I'm really glad that we are looking in the same direction.

Best regards,

Should it be a check with Sh or Sc if operating stresses as per Appendix P are being checked?

Another post by Dave...
http://65.57.255.42/ubbthreads/ubbthreads.php?ubb=showflat&Number=22421#Post22421

“
Appendix P is an alternative set of rules for evaluating expansion stress range. You are still obligated to satisfy base Code rules for stress due to sustained loads. If you worry about "hot sustained", Appx. P does not relieve that concern.”

Appendix P is an alternative to evaluating the expansion stress range only, still the sustained stress equation needs to be satisfied in old fashioned way(i.e, Removing/setting siffness to zero for lifting support).

"setting siffness to zero for lifting support"

This is good. In this way you can spot easily the lift off supports. I didn't know this method. Everyday we learn something. Thank you.

Regards