[PSUBS-MAILIST] Hull Transitions

[Alec Smyth]

A transition from cylinder to cone is a major stress point, particularly if
we're speaking of the transition at the larger end of the cone. If you
visualize which way the plate on each side of the discontinuity will flex
under pressure, you will see they are rotating in opposite directions
around the point they are joined, and this means they will try to "split
open" the weld by increasing the angle at which they intersect. I'm aware
of three approaches to address the problem:

1 - Weld it as if it were a normal cylinder to endcap transition. This of
course will work, but the difficulty is determining up to what pressure it
will work. The standard math (e.g. ABS spreadsheet) will not take the
discontinuity into account. Stiffening the cone as if it were a cylinder
can limit the flexing of the cone, and I've seen diagrams of stiffeners
placed directly on the discontinuity. See for instance Figure 1 on the ABS
spreadsheet.

2 - Use a curved transition piece, similar to the knuckle of a regular
endcap.

3 - Use a forged ring for the transition piece. This puts a whole lot more
material at the discontinuity, since we're now talking a roughly triangular
section rather than plate.

Obviously #2 and #3 are MUCH more expensive than #1 but will also get you
much deeper. I don't have any easy math to tell you how much, you would
want to do FEA on it for sure, whichever of the three approaches you took.


Best,

Alec


On Sat, Jan 4, 2014 at 8:34 PM, Joe Perkel <josephperkel at yahoo.com> wrote:

> Busby is unclear as to how a transition from cylinder to cone is
> accomplished (fabricated). Ala PC 14 for example. Is the weld joint
> reinforced or is it simply an abrupt change in angle?
>
> The issue is relevant in an attempt to reduce volume within the pressure
> hull where only machinery/equipment is intended to reside.
>
> Is there a text or diagram somewhere that covers such transitions?
>
> Thanks
>
> Joe
>
> Sent from Yahoo Mail for iPad <http://overview.mail.yahoo.com?.src=iOS>
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