[PSUBS-MAILIST] reinforcing ring

[Sean T. Stevenson via Personal_Submersibles]

Hank - that is essentially correct. Effective reinforcement of the hull shell entails adding material which will carry shell stresses around the penetration, and while there is a bit of a local effect in the pipe wall that distributes load axially away from the weld, there are rapidly diminishing returns as you move away from the neutral axis of the shell wall. A better solution would be to move to a heavier wall pipe, and then make it shorter. You only need to make it long enough to land the weld with a generous fillet, although longer can't hurt - look at the cross-sectional area of the reinforcement. You should be adding at least as much area as you remove in the hole. The ideal reinforcement would be to cut a much larger hole and weld in a thicker spherical head segment so that the carried load is exactly in-line (with smooth 4:1 weld tapers at the discontinuity) so that you don't introduce stress concentrations at geometric discontinuities. In that case, the pipe wouldn't need to carry any shell stress at all, if the insert was strong enough. Quick and dirty though, you want your reinforcement to keep the stresses as close to their original paths as much as possible. Visualize crushing the reinforcement - easy to do with a thin cylinder. Not so much with a thick disc.

Sean

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-------- Original Message --------
On Nov 11, 2017, 13:11, hank pronk via Personal_Submersibles wrote:

> Hi Sean,
> I am getting started on my motor install in my escape pod while I wait for rov and manipulator parts to arrive.  When the motor assembly was in the aft head of Gamma, the motor was inside a 8 inch id pipe 1\2 in wall.  That pipe protruded through the head and was capped on the wet end with a flat plate reinforced with gussets to the prop shaft tube.   I want to use the same parts except, I want to shorten the 8 pipe so it only extends inside the sphere the depth of the magnetic coupler witch is about 4 inches.
> My theory is that the additional pipe length serves no reinforcing purpose past a couple inches inside the hull.  The section of sphere I am removing weighs 7 lbs and the 4 inch long pipe section weighs 15.82 lbs plus the pipe section has a flange for bolting the prop shaft assembly on.
> Is my assumption that the additional length of pipe serves no purpose for reinforcing?
> thanks
> Hank
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