[PSUBS-MAILIST] port ring

[Sean T. Stevenson via Personal_Submersibles]

Essentially yes, but anything that you weld in as a reinforcement or to increase thickness must be complete joint penetration, and you must take care to align the hull shell with the matching shell that is integral to your hatch.  In the case of the hatch opening where you aren't actually "removing" material from the hole, with a four inch shell wall, you may not require any thickness insert at all - you just need to ensure that the hatch "shell" errs on the side of lesser radius on the inside and greater radius on the outside than the hull shell dimensions.  Viewports or other openings that require reinforcement have to have inserts (or consequent shell derating and then carrying the extraneous weight), but there is no particular reason that they need to be entirely separate components from the base hull shell, as long as the geometry and strength requirements are met.

I am not a fan of weld deposition in order to build up necessary volume. If you need to add material, design it into the insert and keep your welds small and consistent with ND inspection. This was a consideration in my hull design, where I opted for a cast insert of much larger diameter than the hatch itself, but the insert takes the place of massive weld deposition in achieving the desired geometry: it provides a smooth load path from the weld location, where it matches the hull thickness, to the much larger bearing area at the conical interface.  All such inserts have machining allowances on their seats, so that after all welding is completed, the entire hull can be stress-relieved through heat treatment, and then the seats subsequently machined in-situ.  The hatches are also cast and then machined to match. Tough process to DIY though without specialised equipment.

Sean


On April 15, 2016 11:37:48 AM MDT, hank pronk via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>Thank you Sean,If I understand you, I could add thickness to the inside
>or outside of the hull and machine the hatch or port seat into the hull
>and extra thickness ring.  The alternative would be to make an insert
>that is thicker and weld it in.  That is not desirable because the weld
>would be Gigantic, plus it would need to be re-machined anyways.Hank 
>
>On Friday, April 15, 2016 10:56 AM, 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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