Through modelling of a thin wall large bore pipe (DN 1600 Wt: 12 mm), I was trying to see effect of pressure stiffening on the bends, so with changing the default value in configuration/computational control to “yes” and re run the model some changes in Flexibility factors for bends were expected .But I’m getting the same values for Ki and Ko for bends in “miscellaneous report” .

Can anybody help.


Many thanks

Your initial run was likely made with this particular configuration directive set to "Default", which means do whatever the active piping code says to do. So, if you're running B31.3, "Yes" and "Default" are the same.

If you want to make this comparison, make runs using "Yes" and "No" settings. Remember, if you change a directive that will affect the numbers, you must go back to input and re-error check for the changes (in the configuration) to be used.

Ray,

Thanks for quick and prompt reply.

I did it again and now the values are different when we choose Yes (or default) and No.

But as I understood from your post, CII will consider this effect by default under B31.3, so my next question is:

What is the criterion of CII to consider a bend as "Large diameter- Thin wall”?

Is it any D/t ratio or something else?

Many thanks.

Al

You will get 100 different answers from 100 different engineers on this one. However, from B31.3 Interpretations No. 12, Interpretation 12-11, issued Sept 17, 1993:

So, if this Configuration Directive is set to Default, and the active piping code includes this (pressure stiffening) note, we compute and apply the correction factor (consistent with the limitations of the factor).

If this Configuration Directive is set to Yes, we compute and apply the correction factor (consistent with limitations). If the active piping code does not discuss pressure stiffening, CAESAR II uses the equations from B31.3.

If this Configuration Directive is set to No, CAESAR II doesn't apply the pressure stiffening adjustments, even if the code says to do so. This option was most useful following the A96 addenda to B31.1, which was when B31.1 added this pressure stiffening adjustment. Using the "No" setting, you could run CAESAR II and determine SIFs as they were prior to A96.