Dear Richard/Loren,

I understand that using "Default" causes Caesar II to use whatever the current active piping code recommends.

However , I had requests from the Client to set this directive "YES". After the analysis, I saw that GRE allowables went up substantially (some cases more than twice), and does not show any failure in the piping any more.

Because I had a bit difficulty to understand what happens in the background, I need a brief if this approach is adequate since we use GRE material under the ISO 14692 using Caesar II.
At the moment I feel very uncorfortable by setting this option as "YES".

I would like to hear about your thoughts on the issue.
Thanks in advance and kind regards,

Ibrahim Demir

Ibrahim Demir:

I would say that the implementation of ISO 14692 in CAESAR II is adequate.

ISO 14692 has two allowables: hoop allowable and axial allowable. In CAESAR II, since we report only one allowable, we choose the one with greater ratio of (code stress/allowable). So there are twe sets of data:
1. axial code stress, and axial allowable
2. hoop code stress, and hoop allowable
CAESAR II reports either 1 or 2, depending on their ratios.

Because hoop allowable is generally twice of axial allowable, you might see that allowable jumps up or down. That's probable what happens in your job.

Regards,

Lu

Ibrahim Demir:

Adding F/A in stress could change code/allowable report from axial to hoop.

For example, if F/A is compressive, adding it might decrease the total axial stress, and thus decrease the code/allowable ratio. And that might make hoop stress a controlling factor. In that case, CAESAR II will report hoop code stress and hoop allowable, instead of axial code stress and axial allowable.

Regards,

Hi Xiaojun,

I understand your example with F/A in your last reply. However, the results we get after adding F/A in stresses are very confusing and seem to be unreliable, and therefore we turned back to "Default" option. Now, everything makes sense.

We had several temperature trials with short models. We used temperatures in the piping 60, 70 and 80 deg C under different file names, and found that the failure occures at 60 deg C not on others. In these trials we have used the allowables for sigma al(0:1)for given temperatures only the remaining stayed the same. The results we obtained from Caesar II did not make any sense to us to understand why this was happening.

However, we tried the same after using F/A as "Default" the results were as expected, and 60 deg C option has passed the code stresses, and failure stress ratio at one location increased by the increased temperature as expected.

I understand ISO 14692 needs interpretation on the stress evaluation to make everything clearer to the users. However, I see that, if I do not look at correctly, there are some slight differences between ISO 14692-3:2002(E) Technical Corrigendim 1:2005 for Equations 21 and 22 and the equations given in C2Quick.pdf for "Fully Measured Envelope". Since I do not exactly know the background of the standard I cannot easily comment on it.

If you are interested in I can forward the files on you for your trials. However the files are a bit large although they are the short versions, you need to send me direct e-mail address if you are interested in.

Kind regards,

Ibrahim Demir