[PSUBS-MAILIST] port ring

Fri Apr 15 13:34:10 EDT 2016

Rick, if you are using the equal area reinforcement rule, then the idea is to add material around the hole that will carry stress that would have otherwise been carried by the material in the hole. As such, you get a much greater benefit by making your pipe insert of greater wall thickness, than you do by simply making it longer. While some stress can be redirected away from the shell wall, there are diminishing returns with distance. An eight inch long insert is not going to add twice as much strength to the hole as a four inch long insert, which makes sense intuitively. Doubling the insert diameter, however, makes a substantive difference.

That said, you always want to make the smoothest possible load paths without artificial stress concentrations if possible, which means avoiding abrupt 90° changes in geometry. I would size a penetrator insert to be long enough that I could build up a weld bead on it that could be faired back into the hull smoothly, ideally at a 4:1 taper. Better yet, create custom inserts which match the hull thickness at the weld, shaped to optimize the load path across them.

Sean

On April 8, 2016 8:21:05 PM MDT, Rick Patton via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>while were on the subject, I need some clarification on the "replace or
>add
>what you took out of the pressure vessel skin theory" as when I wanted
>to
>add a few extra view ports, I called the captian,Ketterage, and asked
>about
>cutting extra holes in the hull and he said the same thing but then got
>to
>wondering about that statement.
>When you cut a hole in the hull and weld in a piece of solid round
>stainless steel with a 1/2" hole in it for gas/wires, you still have a
>1/2"
>hole in the hull so that theory can only work if you take into
>consideration the amount of ss rod that is also on the inside and
>outside
>of the hull?
>If that is the case, it doesn't seem correct to use a pipe with a 1/2"
>ID
>schedule 40 but you extend it inside and outside until you equal the
>same
>volume as you removed?
>Rick
>
>On Fri, Apr 8, 2016 at 3:34 PM, Stephen Fordyce via
>Personal_Submersibles <
>personal_submersibles at psubs.org> wrote:
>
>> Hi Hank and Sean,
>> Given Hank is probably halfway through building this already and Sean
>> might be in the middle of other things I thought I might jump in - I
>think
>> I can help in general terms.  The rule off thumb is if you make a
>hole in a
>> pressure vessel, you're supposed to put this material back as
>reinforcing
>> around the hole to keep the same pressure rating.
>>
>> So if you want to take advantage of the full 4" thickness (wow!!!)
>and
>> associated depth rating, then you would need to reinforce the hole -
>and it
>> would need to be a pretty serious reinforcement to replace that
>thickness
>> of material.
>>
>> Alternatively, if you don't reinforce, then you lose some of your
>depth
>> rating, because some of the thickness is locally credited as
>> reinforcement.  This means an amount of thickness over the rest of
>> the shell away from the hole is basically dead weight, which may or
>may not
>> be a problem depending on whether this gets lowered or is
>free-floating.
>>
>> To put it another way/thought experiment: if you could machine away
>all
>> the unnecessary material after you've machined the landing area and
>> hole, the result would look like a thinner shell with a reinforcement
>ring
>> welded around the hole.
>>
>> Cheers,
>> Steve
>>
>> PS: All that said, it seems theoretically possible that if you had a
>hole
>> with a spherical hatch and the right angles, and it all mated
>perfectly,
>> that with everything in compression it shouldn't matter there was a
>hole.
>> Probably this doesn't account for the buckling failure mode though. 
>This
>> is getting a bit out of my depth (if you'll pardon the pun!).
>>
>> On Fri, Apr 8, 2016 at 11:22 AM, hank pronk via Personal_Submersibles
><
>> personal_submersibles at psubs.org> wrote:
>>
>>> Hi Sean,
>>> If a guy was to buy a 48inch id CNG sphere with a 4 inch shell
>thickness,
>>> would it be necessary to weld in a land ring and port seat.  Or
>could a guy
>>> or gal rough cut the necessary holes then put their  flange machine
>to work
>>> to machine seats in the shell.    It seems logical to me that could
>be done
>>> for the hatch because the load would be supported by the same steel
>in the
>>> hatch.  Or am I out to lunch?
>>> Hank
>>>
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>>>
>>>
>>
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>>
>
>
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