[PSUBS-MAILIST] port ring

[Sean T. Stevenson via Personal_Submersibles]

I would add that your tolerances on such an interface are quite critical. In addition to the conical angle (where I would probably stick to the PVHO standard of +0.25°/-0° on insert, +0°/-0.25° on seat), roundness, concentricity and thickness minimum (inner and outer radius) need to be considered.

Sean


On April 15, 2016 10:56:22 AM MDT, "Sean T. Stevenson via Personal_Submersibles" <personal_submersibles at psubs.org> wrote:
>It could be done for the hatch, but the interface would have to be
>exactly normal to the sphere surface, otherwise reinforcement around
>the opening becomes necessary, in which case you have to derate the
>shell to match the effective reinforcement provided by the existing
>shell thickness, and are then carrying extraneous material elsewhere.
>This would always be the case for any window seat or other opening
>which you actually remove steel from. If you plan a hatch like this,
>all the same rules apply as for hull shells, with regard to full
>penetration welds and reinforcement around openings for e.g. dogging
>shafts or viewports. Also, the hatch material, if following exactly the
>same shape, must be at least as strong as the shell. 
>
>I ran into this problem on my hull design, where specified limits for
>plate steel strength are given by ABS, but my hatch was going to be a
>casting of equivalent material. According to the rules, castings have
>to be 20% thicker than the numbers would indicate in the absence of
>exhaustive destructive testing to demonstrate equivalence to plate
>material. It wouldn't be a bad idea to go slightly thicker regardless,
>so as to ensure a continuous load path from the hull shell without any
>geometric discontinuities.
>
>In any case, what you don't want to do is machine features into your
>contiguous shell which introduce stress concentrations (screw holes,
>stepped seats etc.) without either adding reinforcement, or derating
>the hull shell accordingly.
>
>Sean
>
>
>
>On April 7, 2016 7:22:26 PM MDT, 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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