Dear all ,

According to B31.4 thermal expansion stress check , it should be
S=SQRT{(Bending stress)^2+4*(Torsion stress)^2}.
I'm so surprised that the result of code stress becomes {abs(Axial stress)+(Bending stress)}.
Did anybody find the same problem before? or Is there something wrong during my input procedure ?

There are different stress values depending on whether the pipe is "restrained" or "unrestrained". These are Code terms. See 419.6.4.
You identify the pipe as restrained or unrestrained by the CAESAR II term FAC. When FAC = 1, the pipe is restrained; when FAC = 0, the pipe is unrestrained.
Perhaps your question is answered here.

Hi Dave ,

There is one example could be described my question clearly.
For B31.4 expansion stress check should be as below (FAC=0.001 unrestrained portion) ,
S=SQRT{(Bending stress)^2+4*(Torsion stress)^2}.
NOW , node=10
Axial stress = -1000 psi
Bending stress= 500 psi
Torsion stress= 0
The code stress should be SQRT{(500)^2+4*(0)^2}=500 , but
the actul result is 1500 psi.
All of the node code stress result in {abs(axial stress)+bending stress}.

Sorry for my poor knowledge , I am confused these results and can't find where the problem is .

I'm appreciated your kindly help....

Regards,

By default for B31.4, where FAC=0.001, CAESAR II will include the direct axial stress in the expansion stress calculation. The paragraph in the Code (419.6.4(c)) does not indicate this increase in calculated stress. But this paragraph also applies this equation: "for those portions of the piping system without substantial axial restraint". Well, is the line restrained axially or not? With FAC=0.001 we're kind of letting the calculations determine this. The Code has "restrained" lines and "unrestrained" lines but no "maybe it is restrained" lines.
If you do not want to include the axial stress term, you can either change FAC to 0 for these elements or change the Configuration parameter "Add F/A in Stresses" to "No" (under SIFs and Stresses).
I cannot, at this time, state how these changes will affect other stress calculations.

Hi Dave ,

Thanks for your kindly reply.
I found that piping stress description stated in B31.4 wasn't not so "familiar".Some equations should be got to know from its words and if
somebody miss some of these sentences ,maybe,it will result in the different thought...