Obround flange design per ASME VIII 3

[esf]

Does anyone have any sources for the design of an obround bolted flange and cover plates for use on a pressure vessel. The obround neck is 27" OD x 30" c/c.

Appendix 2-10 gives a procedure for non-circular flanges with a circular bore which doesn't apply in this case.

The design of the reinforcement of the obround into the head and the thickness of the sides of the nozzle is relatively easy, but I can't find any referance in ASME VIII Div 1 to obround flanges.

Thx.

 

[JoeTank]

ASME VIII, UG-34 covers the design of bolted cover plates. Unforunately, UG-34 does not address the flange portion.

Steve Braune
Tank Industry Consultants

http://www.tankindustry.com

 

[GenB]

In this case because is relatively small difference between the sides 27 to 30 in, you may take the largest and calc as
a circular; hoping that the increase in diameter will not affect the thickness of the vessel wall.
'hope this helps.
ER

 

[deanc]

Review SecVIII Div 1 Appendix 2 and Appendix 13. Then Appendix S and Y. These may be of some help.

 

[arto]

There was an article in one of the ASME PVP volumes from the 1980's:

"Bolted Flanged Connections for Non-Circular Pressure Vessels" by A.E. Blach of Concordia University in Montreal.

Maybe do a search on his name....

 

[esf]

Thanks for the quick responses.
Steve Braune - I had forgotten that UG-34 covered non-circular bolted covers.

generalblr - the flange is actually quite long; 27" short dimension X 57 Long dimension. I have tried calculating the flange in a manner similar to that given in App. 2-10 (ie model it as a circular flange), but it seems to be greatly conservative (I'm looking at a design from another vessel that is similar).

arto - thanks for the info. I haven't been able to dig up a copy of that publication but I have asked both ASME and WRC for assistance. I'll post my findings back here.

Dave

 

[JoeTank]

esf,
I may be able to suggest a method of design, but I'd need you to confirm sizes. Based on your posts, it looks like you have an obround opening of 27"x30". But, the obround flange is 27"x 57". I can't quite visualize what this beast looks like.

Steve Braune
Tank Industry Consultants

http://www.tankindustry.com

 

[arto]

From another thread - Lauper sez it's:
1989 PVP 158, ISBN No. 0-7918-0314-7 that the Blach article is in.

 

[esf]

The opening is 27" diameter in the short dimension x 57" long dim (a 27" dia nozzle split in half and separated by two 30" straight pieces). The flange only needs to be wide enough for the bolts (~ 3" wide).

I can e-mail you a picture if it helps.

Thx.
Dave

 

[JoeTank]

esf,
As an old vessel designer, I have old tricks developed over the years. I think it is one of those procedures that has been handed down from father-to-son. i don't know it's origin, but I learned it from a seasoned ASME Code vet.

Remember that when design rules are not given in the ASME VIII Code you are on your own. At that point you make conservative assumptions, use code allowables, materials, NDE etc as appropriate.

The basic procedure is approximate and is intended to covert the opening into an equivalent circular opening. It goes like this. Determine the cross sectional area of the opening... 27ID x 57ID obround = 1383 sq. in. Now convert it to an equivalent circlular opening = 42 inches ID. Now apply the ASME flange design methods for a 42 ID flange using the geometry of the actual flange. In recognition that this is an estimation of the real condition I have always rounded the required thickness upward a generous amount.

A warning... I have typically limited the use of this method an opening aspect ratio of 1.5:1. Your flange aspect ratio is 57/27 = 2+... far in excess of this personal limit. Although this approach has been succesful for my typical applications, I would only use it an a very rough approximation of a proper design for this case. I wish I could be a real help to you via this forum, For now this may only get you started... more research would be needed.

Steve Braune
Tank Industry Consultants

http://www.tankindustry.com