Nozzles in flat heads

[pbc825]

I'm in the middle of some design review work for a client on a pressure vessel with one loose bolted flat head on each end. Each flange employs a nozzle for the passing of gases in and out of the vessel. One head has an opening concentric with the head, and the other head has an opening slightly eccentric with the head. The manufacturer had supplied calculations for my review with both openings concentric with the heads as per calculations from ASME Section VIII Division 1 Appendix 2. I trust this is accurate for the concentric head, but inaccurate/unacceptable for the eccentric head (comments here are welcome). I've completed a full 3D FEA model and the design is safe; however, I'm interested to know the correct way to do this in design-by-rule and Division 1.

Some details are as follows:
Head OD: 21.5"
Bolt Circle dia.: 18.5"
OD of vessel: 14"
wall thickness of vessel: 0.875"
Opening dia. for nozzle: 6.52"
Eccentricity: 1.19"

There are other openings and features in the head, but the openings are much smaller (next largest opening is 1.22" dia.).

Could someone point me in the right direction as far as the portion of Division 1 the manufacturer should be doing these calculations in accordance with?

Thanks in advance.

 

[SnTMan]

pbc825, sounds as though your vendor is treating the flat head as a loose ring flange, per Appendix 2, rather than going thru the detailed reinforcement calculations of UG-37.

I'd say this is a legitimate approach (which I have used on occasion) if a) there is no attached nozzle or 2) one is prepared to disregard the reinforcement contribution of the attached nozzle, welds, etc.

Depending on the software used it can be more convenient than a UG-37 calculation.

However for the eccentric case, I would take the ID of the loose ring to be equal to a circle concentric with the head which encompasses the opening.

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[racookpe1978]

What operating pressure ?
What fluid and what corrosion allowance?

It is relatively small - which helps a great deal! - but consider ribs on the outside of the flat surface to reinforce against the bending movement. EACH nozzle - no matter how "small" it is - will lower the overall strength of the flat plate.
But EACH nozzle - because it is a welded round cylinder around a hole in the 7/8 plate - will also serve to make the flat plate stiffer against bending - by adding stress risers at each weld. Be careful with this one - local stresses could be very high at each eld if ANY flaws are inside the weld joint.