Hello Fellow Stressers!!

What is the reason why bourdon effect is not default in pipe stress software?

Thanks & Warm Regards,

"Bourdon effects are almost always important in fiberglass reinforced plastic piping stress. For this reason, the Bourdon (Translational) is automatically turned on for all FRP pipe runs and bends" says User's manual.
I guess someone decided that, for steel piping, this effect is not always important, which doesn't make sense for me...

Another question would be why we call the pressure displacement effects in a cylinder as "Translational Bourdon effect"; Eugene Bourdon imagined and patented using the bending of a circular tube made of metal as pressure gauge device and never claimed he discovered the elongation of cylinder pressure loaded or using such effect in a gauge device. Can be named better as Hooke effect in case there is the determination to associate the effect with a person. And frankly speaking, the effect of elongation under pressure depends on the particular condition of the cylinder- that's why in a restrained condition of a pipeline there is no axial elongation.

Thanks Mariog for the information. We have the same opinion on the subject.

Cheers!!

Regarding the Rotational effect, this is only in the presence of ovalization.

Oval section tend to become circular and this cause bend to try to straighten. The forged elbows are circular in section and therefore the Bourdon effect tend to be minor. Since in many applications fabricated bends are not really used but forgings are widely used it is supposed that by default this effect is not a default option.
Of course if you feel that this effect is still important for some reasons (very high pressure or poor manufacturing) the program allow you to activate the option.

The Bourdon tube Pressure gauge is an application of Bourdon effect.

Dan

The very basic and widely used approach in piping stress analysis is to model both categories- pipe bends and elbows- using simple curved beam theory and scale up the stiffness constants and calculated stress using factors that account for the ovalization of the pipe cross section and the pipe internal pressure. For ovalization, these factors were derived by von Karman for in-plane loading and later by Vigness for out of plane loading. I would say that in our Code calculations ovalization and pressure effects in elbows are still in place even "ovalization" is not explicit. In my opinion the real issue with rotational Bourdon (which is a pressure effect) is not ovalization but the fact we already consider the effect of pressure when divide "i" and "k" by factors pressure dependent (see Note (4) of B31J Table 1-1 or notes in the former Appendix D of B31.3).
See also the discussion in http://forums.coade.com/ubbthreads/ubbthreads.php?ubb=showflat&Number=42106

I guess we discuss two different aspects. I am talking about classic Bourdon effect, which is about a partially flattened cross section tube that tend to become more circular due to internal pressure. As an effect of this, the angle will tend to increase. The formula of the bending moments applied at the ends is proportional of the internal pressure and the ovalization. If the ovalization is very low, the moments are also low.
This effect is not addressed by code.

I try to quote from an old post of John Breen in eng-tips:
"Internal pressure can affect the pipe bend or elbow in 2 ways. The Bourdon effect describes the tendency for the pipe bend to "open" under internal pressure [..]. The other effect is the "stiffening" of pipe bends and elbows as internal pressure is increased"
What I try to say is we are counting "2 ways" for pressure but in fact there is a cause (pressure and bending) and an effect. We haven't a good theory to count the effect. We have several theories which are considering internal energy as the basis of their calculation. For bending- we have the Code flexibility and stress intensification, derived from ovalization theory. As for pressure, as quoted above- we ended by having one theory included in Codes (modifying flexibility and stress intensification), while the other is an option.
The problem when splitting such energetic theory in parts (better said in three parts, M_bending, p_Bourdon and p_stiffening) is that we are not able to count the proportion of the energy allocated to each one and here superimposing the effects cannot work. That's why I'm reluctant to consider rotational Bourdon together with "stiffening" under pressure of pipe bends and elbows.
As for "translational Bourdon" I think must be always activated because is related to axial stress- axial strain via elasticity theory.

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