Re: [PSUBS-MAILIST] Pressure Vessels

[Al Secor <wreckdiver@usadatanet.net>]

Hi Cliff,

I'm an EE, not an ME but I'll take a stab at answering your question.  There
really is no correlation between internal pressure burst rating and crush
strength.  Material behaves differently between tension (internal pressure) and
compression (external pressure).  Vessel roundness tolerance is nowheres near
as critical on an internal pressure vessel (the pressure would tend to make it
more round) than an external pressure vessel where the pressure would try to
deform the vessel.  Take the old (plastic) Coke bottle analogy that has been
brought up before in the forum....it takes little effort to crush an empty coke
bottle (with the cap on)...if you were to put it in a pressure chamber it would
collapse with relatively little pressure...try taking one to the bottom of a
swimming pool where the pressure difference would only be about 5 psi (for a
10' deep pool)...However, if you were to internally pressurize it, it would
take several times that pressure before it exploded.

Hope that helps!

Al Secor  ARS: WA3PWX  Scuba Instructor SSI PDIC TDI
http://www.geocities.com/SubDiverI



Quoting Cliff McDonald <cmcdonald@applikonusa.com>:

> Question for you ME?s.  Is there any relationship between crush strength and
> a pressure vessel?s burst rating?  Here in the oil patch it?s relatively
> easy to find scrap pressure vessels in sizes and shapes that could be
> desirable for a psub?s pressure hull.  Materials range from mild steel to
> hastalloy and other exotic alloys.  Many are in good condition and can be
> purchased at fractions of a dollar per pound of material.  Being pressure
> vessels, they tend to be cylindrical, spherical, have rounded endcaps,
> external reinforcing rings, etc..  It shouldn?t be too hard to find the
> manufacturer and get the original application and/or cert?s on them, of
> course all the ratings would be for internal pressures / temps.
> Best Regards,
> Cliff McDonald
> 





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