Re: [PSUBS-MAILIST] old SCUBA cylinder (10% expansion mistype?)

[Alex <spm2@nomad.ignorelist.com>]

I was just thinking the same thing. Shouldn't the tank return to almost exactly
the original volume? Otherwise the steel has exceeded the yeield point.

 You can cycle steel at about 50% of the yeield strength without any fatigue
problems (it's one of the few materials that has this quality.) If you bring it
up to the yield point each time you do that it gets a little bit weaker.
Hardened steels may be different since the rupture tensile strength can be
lower than the yield strength. The tanks made today are made of Chro moly
alloy. They are pressed in to shape and then heat treated and tempered.

The tank has to be useful for something. If there are no markings you can find
the thickness of the metal with ultrasound or weighing it and measuring the
bottom thinkness by sticking something down it. Then you can assume the worst
like 36,000 PSI yield strength and calculate a pressure that would bring it to
18,000 PSI. You could use it for compressed air in a psub!

Alex


On 11-Feb-2012 Marc de Piolenc wrote:
> On 2/11/2012 7:38 AM, Ken Martindale wrote:
> 
>> Expansion was measured with the criteria that volume had to return to within
>> 10% of the original volume after the test pressure was applied.
> 
> Hydro testing allows a 10% permanent expansion? Please tell me that's a 
> mistype....
> 
> Marc
> 
> 
> 
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-- 
Mailed on 12-Feb-2012.



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