Bolt Circle on Pressurized Cylinder
Bolt Circle on Pressurized Cylinder
(OP)
I'm designing a bonnet of sorts on a valve body. I'm looking for codes or formula or something to size the bolts and wall thickness they are tying into.
I've got the minimum wall thickness for pressure containment but its a rather large opening (relatively at least) so a lot of bolt force. The formula i've used so far is pointing to a certain size bolt but i'm worried about the wall thickness between the bolt and the OD/ID. I would like to use the minimum for pressure but it looks a little thin but i'm really trying to control my costs on this thing. FEA is fine but i'm also worried i'm not truly capturing the forces properly, specifically the bending of the threads.
This is a 316SS body with Grade 8 bolts (maybe Grade 5). I've looked at Nut Dilation equations from VDI 2230-1 and it is helpful but the application is a bolt circle and not a nut so there is substantially more material along the tangential of the bolt circle than a nut would normally have so i fear i would be over designing if i used this info solely.
I've got the minimum wall thickness for pressure containment but its a rather large opening (relatively at least) so a lot of bolt force. The formula i've used so far is pointing to a certain size bolt but i'm worried about the wall thickness between the bolt and the OD/ID. I would like to use the minimum for pressure but it looks a little thin but i'm really trying to control my costs on this thing. FEA is fine but i'm also worried i'm not truly capturing the forces properly, specifically the bending of the threads.
This is a 316SS body with Grade 8 bolts (maybe Grade 5). I've looked at Nut Dilation equations from VDI 2230-1 and it is helpful but the application is a bolt circle and not a nut so there is substantially more material along the tangential of the bolt circle than a nut would normally have so i fear i would be over designing if i used this info solely.
RE: Bolt Circle on Pressurized Cylinder
For a design procedure specific to bonnets I don't think you will find one. That being said you are still subject to the design requirements of the code and or standard that you are producing the valve to. There should be some general limit on allowable stress specifically for bolts, and other components. A bolted bonnet is a flanged connection that is not subject to piping loads therefore it need to meet your code requirements for a designed flange. The most widely published flange methodology is the Taylor Forge method incorporated into the ASME code. You should look use the ASME method for bolt sizing in all cases, and possibly for flange and wall thickness as well. Roark's formula for a fixed outer edge plate with a free inner edge is also a conservative estimate for flange thickness.
Are you concerned about the tapped holes in the bonnet being too close to the valve bore or are you worried about the bolt circle hole being too close to the OD of the bonnet?
RE: Bolt Circle on Pressurized Cylinder
MJCronin
Sr. Process Engineer