In ASME B31.3 there is a piping flexibility factor that is applied to various components. The flexibility factors for some components are given in Appendix D of this Code. How is this factor used by CAESAR II?

Can CAESAR II calculate the flexibility at bends due to local flexing, (ie. ovalization) to increase the flexibility of a piping system? How does it do this?

[This message has been edited by Brian Cooper (edited April 17, 2000).]

CAESAR II internally computes the flexibility factors (and SIFs) described in the piping codes, Appendix D for B31.1 and B31.3. When necessary, these values are adjusted (in accordance with the codes) for <em>flanged ends</em>.

In the case of the flexibility factors, these values are used in the construction of the <em>local</em> element stiffness matrix, which in turn affects the <em>global</em> stiffness matrix and thus the overall displacement solution.

The purpose of these flexibility factors is to account for the local flexing (ovalization) of the bend. This is why all other components have a flexibility factor of 1.0.


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Regards,
Richard Ay (COADE, Inc.)

What are the paramaters that go into the calculation of the Bend SIF.Why is my SIF and Flexibility factors changing on the introduction of pressure.Consider this case of mine.

A 6" sch 40 pipe ,1.5D radius elbow.I checked the SIF using the "review SIF facility " the following were my observation

SIF Inplane = 2.26
SIF Outplane=1.888
Flexibility Factor = 6.59

The above check was with zero pressure and B31.3 as the code.Next I added a pressure of 2000KPa

SIF Inplane = 2.205
SIF Outplane = 1.837
Flexibility Factor = 6.435

I checked the following things in K-aux to be certain
a)Pressure Stiffening is None
b)Bourdon Effect is None

My Questions

1)Why is my SIF and Flexibility Factors changing on the introduction of Pressure.There is some sort of stiffening occuring?.
2)If I am correct Pressure Stiffening and Bourdon Effect settings in the K-aux do not affect the i and k values?.
3)The pressure stiffening in the config set up affects the i and k values .Maybe this is the missing link , how does it affect?.
4)SIF and Flexibility factors for a elbow are dependent on the radius of the pipe , bend radius and thickness.That means a 45 Elbow and 90 Elbow having all these paramaters same have matching k and i values?.
5)Lastly , increasing the elbow radius decreases flexibility (Loads increase) and decreases SIF (Stresses come down).

Thanks in Advance

Caesar modifies the SIF's and flexibility due to pressure stiffening. Look at the notes at the end of the B31.3 table to see the equations for pressure stiffening.

Casaer automatically applies pressure stiffening on bends etc using the MAXIMUM pressure load. I think this is not a good way to do it. I think it should apply different pressure stiffening for each pressure load case, corresponding to that load cases pressure.

Are you sure you turned the pressure stiffening off in the correct place on Caesar. You can do it in 2 places. 1- the special execution parameters, or 2 - configure/set-up => computational control.

The one in the special execution parameters is for pressure stiffening of straight pipes, it is not the one you want

The one in the computational control is for bends, tees etc. It will turn the pressure stiffening on SIF's and flexibility off.