SIF at high temperature & 20% relaxation in allowable stress

I am doing analysis of a line with 700 degree Celsius temperature. Pressure is 10.9 barg. The line material is A312 tp 304H. Questions that I need to ask from you all are:

1. Is it ok to take SIF as 0.75i for sustained case? In my opinion, as sustained stresses cause the failure in creep, so I should not do it but need your expert opinion on this.

2. In some cases the line goes at higher temperatures, which are the worst case for this line. The duration of those cases is satisfying the conditions of event being less than 20 hrs and maximum of 500 hrs per year. Should this relaxation of 20% addition in stresses (ASME B31.3) be given for this high temperature (783 degree Celsius) for which normal operating temperature is 700 Celsius?

3. Is this 20% relaxation applicable for the thickness calculations as well generally?

For my model, I am getting the same stress values with and without application of Wc Factor (The circumferential weld strength reduction factor). What mistake I am doing here as I should get higher values if Wc has to be considered for circumferential welds?

Please help!

B31.3 changed the requirements for applying W in longitudinal stress calculations. Now it is up to the designer. So in the current version of C2, we have a switch in the Configuration file to turn "Wc" on and off.
Check the status of that switch.

Mr. Diehl,
I set this switch to false.
Ran the error checker and then ran the analysis.
No difference in the stress values!
So what may be wrong here?

Are you looking at Code Stress or Allowable Stress? W adjusts the allowable stress for sustained load, not the sustained stress.

I have a question about caesar II v530.
When I make load case wind or seismic, what does it load case type?
OCC or OPE I think OCC.
But If T1+P+WIN 1 (occ) Sa=ShX1.33
T1+P+WIN 1 (OPE) Sa=1.25(Sh+Sc), Appendix P fixed in config.
how to solution to tell me.

Mr. Diehl,
Neither code stress nor allowable stress is changing!
I am missing something here!

What is your value for W?

Hallo Dave,
Dave I too faced this probelm
There was no change in the sustained allowable stress .For both true and false condition the sustained allowable stresses remain unchanged .
In my case the pipe was A335 P11(CrMo) and the temperature was 454 deg C.
W value comes out to be 0.95 as per Table 302.3.5 of B31.3 2010 edition.

Suri,

Do you see the value for Wc in your input?

If you cannot figure it out, log a support request at ecustomer portal. Also tell us what version and build of CAESAR II you are using.

For International customers please use this link to request support:

http://www.coade.com/dealer.shtml

For US & Canadian customers, go to eCustomer (https://crmweb.intergraph.com/ecustomer_enu/) if you already have a login. If you do not have a user login, click here (https://support.intergraph.com/OnLineSupport/accountreq.asp) to request one. If you are a maintenance customer, you have access to our knowledge base, technical tips, and downloads.

If you can't figure it out, log a support request ... This is ok but for the rest of the forum users, we may like to know the answer to this puzzling question. Would it be possible to post the answer on this forum?

Regards,

Pat LaPointe