[PSUBS-MAILIST] Terminating a conical transition

Sat May 3 10:50:28 EDT 2014

It worked very nicely that way for all us Perry kids.
Vance

-----Original Message-----
From: Sean T. Stevenson via Personal_Submersibles <personal_submersibles at psubs.org>
To: Personal Submersibles General Discussion <personal_submersibles at psubs.org>
Sent: Sat, May 3, 2014 10:28 am
Subject: Re: [PSUBS-MAILIST] Terminating a conical transition

Or a single eccentric conical section?
Sean

On May 3, 2014 8:03:36 AM MDT, via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
Joe,

It seems like an expensive and complex assembly for what you get. Why not close the aft segment in a simpler way and fair the stern to the shape you prefer? A hemisphere with an extended shaft housing to put the prop where you want it, for instance.

Vance

-----Original Message-----
From: Joe Perkel via Personal_Submersibles <personal_submersibles at psubs.org>
To: Personal Submersibles General Discussion <personal_submersibles at psubs.org>
Sent: Sat, May 3, 2014 8:17 am
Subject: Re: [PSUBS-MAILIST] Terminating a conical transition

Sean,

Yes, a bolted flange with O ring.

I've attached an image of what's on my mind. This hull is 36" OD, cylinder length is 120". Anything bigger in diameter, simply gets way to big and bulky for handling.

I'm thinking at this size, I must bolt at least two hull sections together for outfitting and maintenance, and the cones can be un-stiffened or perhaps only at the joints.

Joe

  On Friday, May 2, 2014 9:50 PM, Sean T. Stevenson via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

Each cone section in that case is considered alone, so if you were using stiffeners, you would need a heavy stiffener at every joint. Depending on the size, it may be simpler to use unstiffened geometry for such an assembly.
The rules do not address bolting pressure hull sections together, but I don't see why you couldn't, provided you meet the requirements in terms of the stress analysis under the maximum combined loading conditions, which are prescribed in the ABS rules. Might require some FEA to be sure. You're thinking an O-ring groove seal? Or other arrangement?  I think an ASME code compliant flange would be a good place to start, but I would make sure that the cross-sectional area of each half of the flange considered individually met the requirements of a heavy stiffener per ABS, at a minimum material location (bolt hole). I would also be inclined to use SuperBolts for the connection. 
http://www.nord-lock.com/superbolt/multi-jackbolt-tensioners/
Sean

On May 2, 2014 6:03:21 PM MDT, Joe Perkel via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

Sean,

Would the heavy stiffener rule apply equally to several cone segments stepping down at different angles?

Also, do ASME pipe flange specifications translate equally to bolted pressure hull sections? Have I missed a section somewhere on bolted cylindrical sections?

Very helpful Sean thank you!

Joe

Sent from Yahoo Mail for iPad

                                                            From:                                                        Sean T. Stevenson via Personal_Submersibles <personal_submersibles at psubs.org>;                            
                                                            To:                                                        Personal Submersibles General Discussion <personal_submersibles at psubs.org>;                                                                                                     
                                                            Subject:                                                        Re: [PSUBS-MAILIST] Terminating a conical transition                            
                                                            Sent:                                                        Fri, May 2, 2014 11:45:11 PM                            

2:1 semi-elliptical heads are usually fabricated with some length of straight flange (tangential cylindrical section) beyond the axis of the ellipse. Hemispherical heads may or may not have a straight flange section, but in either case are permissible to use adjacent to conical sections, provided all other requirements are met. For stiffened cones, you must have stiffeners meeting the "heavy stiffener" criteria at both ends, as close as practicable to the cone-to-cylinder and cone-to-head transitions. For unstiffened cones, the length L_c used in overall buckling calculations must be the total length between the next heavy stiffener to either side of the entire compartment length, or between the 40% of head depth points if otherwise unbounded.  Cone to head welds are done in the same manner as cone to cylinder welds, and if your head is supplied w! ith aflange, it is the same thing.
Sean

On May 2, 2014 2:48:52 PM MDT, Joe Perkel via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

I have spotted the ABS diagrams and specifications for re-enforcement and butt welds at conical to cylinder transitions. I am somewhat unclear however as to terminating at the head.

For example, the diagrams in the 2014 ABS underwater vehicles and hyperbaric chamber publication shows conical transitions either bordered by a cylinder at either end, or simply open at the small end???

 I want to terminate the small end of a conical transition directly to a small diameter hemi-head without another straight section, but I am unclear as to whether or not that is acceptable in practice.

Joe

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