Stress categorization in an elbow

[Paulettaa]

Dear all

How would you categorize stresses in an elbow due to internal pressure?
Is it ok if I take membrane stresses as primary and bending stresses as secondary?
I am talking about a ninety degree elbow with stresses considered at the 45 degrees section. The elbow is attached at both sides with pipes of the same thickness and very long.
If the membrane stresses are primary should I consider them as local or general?
And finally what about stresses close to joint with pipes? Are they different?

Warm Regards

 

[DriveMeNuts]

In my opinion, the stresses and distortion are too complex for the elastic stress categorisation method. I would limit M+B as General Primary, however you get all sorts of compressive stresses and distortion around the top and bottom, so perhaps a buckling assessment also needs to be carried out, which takes you into Elastic Plastic analysis anyway.

The quickest and best option is the use a design by rule method.

Have you seen Section 5.2.3.2 of ASME VIII Div 2?

5.2.3.2(b) Components that experience reduction in stiffness with deformation, e.g., a pipe elbow under in-plane bending, shall be evaluated using 5.2.4.

 

[TGS4]

I would also refer you to paragraph 5.2.1.2

 

[Paulettaa]

Thank you for your advice.