Design of spherically dished covers (bolted heads)
Design of spherically dished covers (bolted heads)
(OP)
Design of spherically dished covers (bolted heads)
ASME IIIV Appendix 1 1-6
I am trying to optimise a design of a bolted head similar to FIG 1-6 (D) with regards to the thickness of the flange T.
My design differs from the figure (D) by the fact that the seal is carried within the flange in a groove, this groove would typically be 0.375 deep, and the bolting is achieved by lugs welded to the outside diameter of the ring.
Up to now our standard calculation technique would be to calculate the centroid using the flange area less the seal groove, then the calculate the thickness required this thickness is then said to be the minimum distance from the bottom of the seal groove to the top of the flange.
My question is does anybody know of a acceptable calculation which would allow me to consider the whole thickness of the flange not just the material above the seal as the flange thickness?
Thanks
Dave
ASME IIIV Appendix 1 1-6
I am trying to optimise a design of a bolted head similar to FIG 1-6 (D) with regards to the thickness of the flange T.
My design differs from the figure (D) by the fact that the seal is carried within the flange in a groove, this groove would typically be 0.375 deep, and the bolting is achieved by lugs welded to the outside diameter of the ring.
Up to now our standard calculation technique would be to calculate the centroid using the flange area less the seal groove, then the calculate the thickness required this thickness is then said to be the minimum distance from the bottom of the seal groove to the top of the flange.
My question is does anybody know of a acceptable calculation which would allow me to consider the whole thickness of the flange not just the material above the seal as the flange thickness?
Thanks
Dave





RE: Design of spherically dished covers (bolted heads)
I will research further and post.
genb
RE: Design of spherically dished covers (bolted heads)
te=2AF/(A-B) where AF is the area of flange cross section (and of course taking away also any corrosion allowance from that).
This procedure is adopted by App.G of EN13445, that contains a quite complex method (50 pages) for calculating ring flanges, that is an evolution of App.2 method. In this method however the flange is still considered as a circular ring resisting by bending around an axis perpendicular to the axis of the ring.
If you can adopt that standard, I'm sure it would help you in optimizing your project (but personally never did such a calculation).
If you stay with Div.VIII I think you can still justify the above formula: in fact App.2 calculation relies onto the resistance modulus of the flange around a centroidal axis perpendicular to flange axis, and this one is proportional to the square of flange thickness: hence that way of calculating the effective flange thickness is conservative.
Unfortunately cannot propose a bibliographic reference for such a reasoning under ASME VIII coverage.
prex
http://www.xcalcs.com
Online tools for structural design
RE: Design of spherically dished covers (bolted heads)
The current route I am taking is to model the flange in a FEA package. I have calculated thicknesses from ASME of a standard flange with no groove, and have FEA results for the ASME design. I am now developing the shape of my deep groove design keeping the deflection and stress levels below that of the original ASME design.
Unfortunately the section of the ring is no longer constant, the OD is not round and the ID can only be estimated therefore the EN 13445-3 calculation G.5-7 may not apply
As a alternative I intend to proof test with strain gauges to ASME UG101.
Would you consider this to be a sound proposal.
Best Regards
David
Dave