Testing Old MK15 spheres

Drmike

Ive got 3 old spheres that I want to get tested - does anyone know how? Is it the same tests as with normal scuba tanks or is something else done. Never having had tanks tested before what is the procedure?

They are inconels does anyone know what the test pressure should be?

Cheers
Mike

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Dave Sutton

Send 'em here and I'll test 'em and send them back *if they pass*. If we condemn them, we'll keep 'em and will not charge you for disposal.... Ask no other questions my friend....

Basically, the most important test is not a hydrostatic one. It's NDT testing of the weldments and visual for lack of dents. The NDT was done when they were new... it's not going to change, especially on corrosion-free Inconels. These went thru 100% X-Ray tests when they were new. Why do it again? Maybe if you suspect the sphere has been filled 10,000 times... look for new cracks. Send them out for X-Ray to any good NDT place and see what they say.

Ran a hydro facility at the diveshop for 7 years, so take this from that perspective: Elastic v/s Plastic limits are what a hydrostatic test checks, by looking at the permanent expansion after a pressurization cycle. Every fill cycle of a pressure vessel results in a slight permanent expansion. We're looking for the beginning of exiting the elastic limit and entry to plasticity. Not more than a 10% permanent expansion as compared to the initial expansion when pressurized to 5/3 normal pressure is the baseline test. Cylinders expand to a surprising degree: An Alu-80 will expand about 80 CC's when pressurized to 5/3 working pressure. Permanent expansions are generally on the 1 CC order. If the thing maintained an 8 CC permanent deformation... you're reaching plastic limits. I've put a cylinder on a surface plate with a dial indicator on the side and filled it... and watched that dial indicator run right on up the scale. Try it. A hydro test is done to confirm that a cylinder has not yet reached it's *fatigue limits*, not for much else.


Personally? I would not bother to hydro an Inconel cylinder, as the chances of it's being cycled so many times that it's reached the end of it's life is almost zero. More important is the external physical condition, as dents, deep scratches, etc., all are bad news from a stress-riser standpoint. The military condems these for scratches and dents that are obscenely small... but then again, cost is no object. I'd love to get what they call "scrap".


Dave

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chunter

I'm sure they are not safe. I'll take them off your hands.

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hoppyinca

I've talked with "Jeff", the owner? of Tavco.

he is extremely cautious when discussing the spheres, as they are not DOT. In fact he questioned how I got them... thought they were stollen?

anyway, he told me directly that Tavco will only inspect spheres coming from and going back to the military.

He would not even confirm the method or criteria used for testing. Nor was he willing to to discuss the lifetime cycle limit (was looking for a "from the horses mouth" confirmation of 10,000 cycles).

either he has been burnt before or as a small business owner is way paranoid... which doesn't mean everyone is not out to get him...

all he would say is that they were designed for "special use in the military", not for civilian use.

I can see the potential for liability so I don't blame him, big bummer for us Mk15.X owners though...

hoppyinca

streamway_explorer

Email Colin for the name of the company in Sydney which can do them.

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Michael Collins

www.trimixdivers.com

jhaaja

At least in Europe the pressure is 1,5x the rated working pressure.

JH

Amphibiman

Hoppy, you stole them from me didn't you. Now give them back.

Robin

hoppyinca

I know not the theft of which you speak...

these are not the rebreather parts you are looking for...

hoppy

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