Welded Circular Flat Head with Stiffeners - Design

[RJW000]

I'm looking at a welded flat head on a vessel. This equipment is low-pressure (~6 psig), not code-stamped. The welded flat head (~100" OD) has four C-channel stiffeners welded to head.

Does anyone have any recommendations to evaluate this component and determine a required thickness (only load case is int. pressure)? If it was a VIII-1 vessel it looks like U-2(g)/App-46 may be the correct approach.

Using VIII-1 flat head calculations with no stiffening effects results in required thickness much larger than the original design thickness.

 

[DriveMeNuts]

What is the arrangement of the four C-channel stiffeners?
Are they parallel across the flange?

 

[Some Curious Guy]

We usually design stiffened flat heads as some sort of rectangular plate element fixed at all edges. The boundary of this rectangular element is made up of Stiffeners. Stiffeners would divide the flat plate into many such rectangular elements. Find out the max thickness and that would be the thk of entire plate.

We also have to check whether the stiffeners are capable to act as fixed supports to these rectangular elements. We can do this by assuming stiffeners aa a beam and limiting its deflection to some very minimum value. I do not recollect a number here.

You can find some guidance in handbooks like Dennis Moss, Megessy , Roark formula for stress and strain etc.

The junction between shell and flat plate also needs to checked for any discontinuity stresses. I think here you can follow the suggestion given in Fig UG-34 of BPVC Sec VIII Div 1.

In short you have to use basics of strength of materials and engineering judgement in this.

Best of luck.

 

[goutam_freelance]

Div 1, Appendix 46 permits design by analysis. So FEA is a convenient way of doing this.

Engineers, think what we have done to the environment !

https://www.linkedin.com/in/goutam-das-59743b30/

 

[RJW000]

@DriveMeNuts - This is correct. They are parallel across the head, about equal spacing.

@Some Curious Guy - Thanks for the input, will play around with this.

@goutam_freelance - I understand this, looking for closed-form approximation.

 

[DriveMeNuts]

The cover is essentially a simple beam welded across the opening. Treat each stiffener and adjacent head material as a beam.
The problem with this design is that the small area of head-cylinder weld at the end of the longest stiffener takes essentially all of the pressure load, therefore needs to be beefed up by some amount. Deflection of the beam will also be a needed consideration.
The remaining weld around the side is essentially a seal weld.