pressure vessel testing

Russell,

I know [or at least believe] that you are just being provocative 'for the sport of it', but I would just like to make a couple of points before we let the thread get back on track:

1. "A litre at one bar has only the potential energy of the mass of fluid" might reasonably be thought to have a subtly different meaning to "A litre at one bar has only the potential energy in the mass of fluid" ...

2. If you insist on interpreting 'of' as 'in' ... then the substance of the boiler would have rather more 'potential energy' than its contents.

MichaelG.

No regulations for removable cylinders below 500cc as what Shaun stated 3 days ago.
Time expired on that one is because its aluminium though no law its an understanding of European manufacturers covering themselves in the event of a failure. This came to light around 2006 with Anchutz and a recall of certain dated cylinders.
ie send back an in date cylinder with visible stress cracks, its brushed aside and new cylinder might be sent out.

Therefore the scuba IDAS testing wont apply but can be done as a one off if you supplied the fittings to go on to their test equipment.
Generally make cylinders and any component able to withstand 1 1/2 times the operating pressure as a minimum. Some producers go by the tube rating ignoring any threads, pins, breakouts or weak points.
Used to take mine round to Shaun 20 odd years ago operating pressure 232bar, pressure test took one cylinder with end plugs to 6600psi where the off the shelf 1/8"BSP hydraulic grease gun nipple sheared. Likewise last year good to know the European producers using 1mm pitch threads around 10mm long are fine, Shaun will tell the length of thread in cylinder where thread sheared out, substantially less than 10mm.

Thank you guys, didnt expect to get this much response this has been of great help.

as you can see, bodge has found a walther unit £140. thats probably the price of a 7ltr diving cylinder

very expensive, thats why i started to make these cyls, until the testing obstacle arose, think i might get there now with the forum help.

Cheers..

Re the 'don't use beyond' date on some Aluminium pressure vessels.

For those not familiar with fatigue life charts, whilst steels will show infinite fatigue life if stress is below some minimum value, this is not the case for aluminium where fatigue will proceed even at very low stress levels. Basically you can't totally design fatigue out of an aluminium item that is subject to cyclic loading.

Where monitoring number of pressure cycles is impractical, inspection is difficult (or expensive compared to replacing the item with new), a rate of applying pressure cycles will be assumed and used to calculate an end of useful life date.

I've recently seen such expiry dates on hydrogen cylinders (fuel tanks) for fuel cell powered vehicles.

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That's a VERY useful summary, David

Thank You.

MichaelG.

Jon, the most recent interpretation of the PED that I have seen is that the 1 1/2 times test pressure should be applied to the safety valve release pressure not the operating pressure. This makes the test pressure higher than just using expected working pressure as your starting point so is a more rigorous test. It is because it is possible for the operating pressure to be at fault at higher than nominal pressure and the system can still work as normal.

Martin

> Basically you can't totally design fatigue out of an aluminium item that is subject to cyclic loading.

Such as a DeHavilland Comet

I do worry about the first generation of alloy mountain bike frames... I wouldn't hurl myself down a hillside on one from the early 1990s.

Neil

The move by SodaStream [10 or more years ago], from Steel to Aluminium cylinders is of some interest. There was presumably some clear business advantage to this, but the safety aspects are a little worrying. ...

The company makes it reasonably clear that the cylinders are rented, not sold, and that they should not be unofficially re-filled ... but that does happen.

I would be grateful for any comment from the wise ... Does SodaStream individually test the returned cylinders, or scrap them when time-expired, or what ?

MichaelG.

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P.S. I have a sufficient supply of the old Steel cylinders to meet my needs; but the question is generally relevant to this discussion.

**LINK**

MichaelG.

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P.S.  Follow the hyperlinks ... there are some great pictures.

Edited By Michael Gilligan on 18/01/2016 11:23:30

Thanks!

When I was a boy I wanted to work at the RAE doing exactly that - putting together crashed planes to work ou what had gone wrong.

Neil

Michael,

RE Sodastream cylinders. I have no specific knowledge but;-

1. Just because it is possible to design an item in steel with infinite fatigue life, that doesn't mean that approach was taken - could just as easily have been designed for a safe life of a certain (large) number of cycles.

2. Steel is generally more vulnerable to corrosion than Aluminium is, internal corrosion of steel vessels is an inspection headache. External corrosion is a problem too.

3. Probably other factors to consider too, like resilience when dropped or otherwise mis-handled.

Without more detailed information it's difficult to reach any conclusion about any potential differences in safety levels between cylinder types and their associated inspection regimes.

Thanks, David ... That's useful comment.

The old SodaStream cylinders were very heavily built [for their capacity] and, rightly or wrongly, I feel 'comfortable' with them. ... They are a useful benchtop source of compressed gas.

If I understand correctly, the move to Aluminium coincided with the change to a proprietary screw fitting and the introduction of some strict licencing rules. [probably as a defence against Product Liability claims]

Despite which: Adapters are widely available, and therefore people can and do refill the Aluminium cylinders.

MichaelG.

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Edit: This is the sort of 'information' that worries me ...

[quote]

• Carbonation Cartridges. This is the biggie. The cartridges are reasonably easy to get and exchange for a refill (at some stores, but generally online) in the US, UK, much of Europe, Australia and New Zealand.  In other places, you’re likely to have to refill them yourself (see video at the bottom of this article on how to do it — this is what many cruisers in the Caribbean and Mexico do).  You can getb systems that use “small” cartridges good for making 60 liters of soda or “large” cartridges good for 130 liters — and the interesting thing is that the SodaStream units are the same size, and some can use either size cartridge.  You cannot take carbonators on an airplane (either in the cabin or in checked baggage) and they cannot be shipped by air.
• [/quote]
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Edited By Michael Gilligan on 18/01/2016 15:07:38

Edited By jason udall on 18/01/2016 15:43:18

Edited By jason udall on 18/01/2016 15:41:49