[PSUBS-MAILIST] port ring

[Sean T. Stevenson via Personal_Submersibles]

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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