[PSUBS-MAILIST] pressure test

Fri Nov 18 07:53:11 EST 2016

Hi Steve,When I started testing ports, I filled the pot with water to avoid built up stored energy, plus I sat in the safety of my submarine (bomb shelter)  Hank 

    On Thursday, November 17, 2016 8:38 PM, Stephen Fordyce via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

 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! ldprovide 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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