Stress categories

[poriya]

Hello everyone
Does any one knows the meaning of this sentence in asme sec iii, nb. IT IS a note in stress categories section.
If the bending moment at the edge is required to maintain the bending stress in middle to acceptable limits, the edge bending is classified as pb otherwise is Q.

Thank you in advance.

 

[TGS4]

Yes, I clearly understand the meaning behind that statement.

Do you have confusion regarding this? If so, what is your question?

 

[poriya]

Thank you for reply. I didn't get the meaning. Would you please explain it more.
It isn't clear what the bending stress in middle is
Thank you in advance.

 

[TGS4]

Which part don't you understand? The "bending stress" part, or the "middle" part? You do understand what the limits on the bending stress in the middle of the flat plate are, right?

 

[poriya]

I do not understand what the limit of bending stress in middle of flat plate is!!!
If you have any source to introduce, I will appreciate it.

 

[DriveMeNuts]

Poriya,
Are you saying you do not understand how to classify the bending stress at the centre of a flat head?
Or are you saying you can't find the table in the code where it specifies the classification of the bending stress at the centre of the head?

 

[poriya]

Thank you for reply
So it say that if bending moment in edge of the head is required to maintain pb in middle of the head in acceptable range, bending stress is classified as pb.
How we could find that bending moment in edge is maintaining the pb in middle in range?

 

[DriveMeNuts]

You don't find. You decide.
If the bending stresses at the edge is less than Pb, then it is allowed to be considered to provide support to the centre of the flat head.
If the bending stresses at the edge is greater than Pb, then yielding is occurring at the edge. This means that the edge is considered not strong enough to provide support to the centre of the head. In this case you need to re-run the calculation as though there is no support to the edge of the flat head (The head needs to entirely support itself).

You could decide to increase the thickness of the cylinder welded to the flat head to bring down the stress at the edge below Pb. This means that you could then take advantage of the bending stresses around the edge to support the centre of the head.

 

[poriya]

Thank you my friend.