[PSUBS-MAILIST] pressure test

[Stephen Fordyce via Personal_Submersibles]

Hi Hank,
Speaking of implosions - I had a 100mm diameter acrylic cylinder (~200mm
long with aluminium endcaps) implode in my pressure pot at 10bar/150PSI.  I
thought it was small enough not to worry about putting stuff inside, and
that it wouldn't implode anyway...

The noise of the implosion was enough to make my ears hurt (standing 1m
away from the pot, and despite the pot having a double stainless steel
wall) and I also spent a long time afterwards picking about a million
pieces of acrylic out of the bottom of the pot, which was thankfully ok.

I also have a diver friend who made an experimental housing from PVC pipe
and it imploded at 30m while testing.  He had it clipped off between his
legs and even though it was half full of sand he reckons he literally
nearly lost his marbles.

I guess stored energy for implosion vs explosion just volume and difference
in pressure.  And a lot!  I'm a lot more mindful of implosions now...

Cheers,
Steve

On Fri, Nov 18, 2016 at 2:25 PM, hank pronk via Personal_Submersibles <
personal_submersibles at psubs.org> wrote:

> The test will be conducted with my sphere partly filled with water to
> reduce air volume.  The chamber will be filled with water, so I can't see
> there being any violent reaction should the sphere collapse or the port
> explode.   Your right, I am sure, they are being diligent.  After all, some
> guy  wants  to throw a home built sphere in there very expensive pressure
> pot.  Can't blame them for being carefull.
> Hank
>
>
> On Thursday, November 17, 2016 5:35 PM, hank pronk via
> Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>
>
> Sean,
> Again, thank you, you are very generous with your time to answer these
> questions.
> I hope to have a test date tomorrow, but they are asking about materials I
> used to build the sphere.  They are likely worried about damage to their
> equipment.
> Hank
>
>
> On Thursday, November 17, 2016 5:09 PM, Sean T. Stevenson via
> Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>
>
> According to the ABS rules, the usage factor eta as implemented in the ABS
> calculations runs from a minimum of 0.5 (2x safety factor) for buckling
> modes, to a maximum of 0.8 (1.25 safety factor) for inter-stiffener
> strength. This implies that ABS is ensuring that for equivalent critical
> pressures, strength failure occurs before buckling by varying the value of
> eta, such that the limit pressure for any particular failure mode is the
> theoretical onset of failure (i.e. crush depth), and the limit pressure
> multiplied by the corresponding eta value for that mode of failure gives
> the maximum allowable working pressure. The lowest of the maximum allowable
> working pressures for each mode gives the maximum allowable working
> pressure for the vessel, which corresponds to the maximum allowable rated
> depth. Without any additional safety factor imposed by the operator, this
> maximum rated depth is also the maximum allowable operational depth, which
> wou! ld provide a minimum safety factor of 1.25 from crush, which would
> occur by inter-stiffener strength failure.
> Thus, for a nondestructive chamber verification test, you could test to
> any depth within the maximum allowable, which would be at 0.8 times the
> design failure pressure.  For destructive testing (i.e. a verification of a
> novel design), you would use the 0.2% limit strain criterion to determine
> the failure point, and accordingly define the maximum allowable working
> pressure to be 0.8 times that value, or the design value (whichever is
> less).
> Sean
>
>
> On November 17, 2016 5:55:28 AM MST, hank pronk via Personal_Submersibles <
> personal_submersibles at psubs.org> wrote:
>
> Hi all,
> I am just getting a pressure test organized in a chamber in Burnaby, but I
> have some questions.   Does the safety margin change with deeper diving
> subs?
> What is the rate of pressurization?
> Hank
>
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