Safe working pressure for aluminium tube.

[Mark P.Participant @markp]

[Mark P.Participant @markp]

Hi all I am on the quest for information.I am just about to start a new project which requires me to make an aluminium air receiver of 30mm O/D and 600mm long, they have to hold 1000 psi,now would a 5mm wall be enough to withstand this pressure both ends will be threaded for fittings.

What does the team think.

Regards Mark P.

[DMBParticipant @dmb]

Hi Mark, Pressure of what? Air, Water, Steam? If its steam, forget it – they don`t like each other!

John

[Clive HartlandParticipant @clivehartland94829]

I think drawn aluminium tubing would be totally unsuitable for this project. As far as I know all aluminium air bottles are forged/ formed in one go and are annealed.

I am sure there will be other opinions about this.

Clive

[MadMikeParticipant @madmike]

My initial reaction is to say don't do it.

What alloy do you intend to use?

Who will certify its integrity for you? Sub aqua cylinders are al;uminium but I am sure they do not go to 1000 psi. I would get some calcs done before you proceed. Air cylinders do not normally have a screwed plug in each end. Remember that air receivers at a mere 100psi have to be inspected on industrial premises, and they are normally made of steel.

IMHO you may be making a cylinder that could go off like a bomb. I do not wish to sound disparaging about "Model Engineers" and I do not know the extent of your experience and knowledge but I would seek help from a qualified engineer on this one. Other opinions are available but other lives are not.

[Jens Eirik Skogstad 1Participant @jenseirikskogstad1]

Better to buy the pressure bottle who is approved and certificed then you is not playing with your life to make own pressure bottle. Get rid of your idea to make pressure bottle since 1000 PSI (about 70 Bar) is dangerous and can explode and perforate your body with metal bits!

[Ady1Participant @ady1]

both ends will be threaded for fittings

—-

Have a look at high pressure airtanks or any pressure vessel

They are NEVER threaded at each end

 

There's one wee hole with at least an inch of very high quality high TPI threaded fitting on a scuba or a BA set

 

I'm not actually very safety conscious but I wouldn't do a high pressure vessel in aluminium either

 

edit

Dunlop stopped doing high pressure tests with air on their tyres when a big lorry one blew up and killed about 5 bystanders at the test

After that incident they always used water

Edited By Ady1 on 21/12/2012 00:33:04

[Jeff DaymanParticipant @jeffdayman43397]

Mark P –

The material and construction of the vessel you describe are completely wrong for the purpose you describe, and you should absolutely not build it as described. As others have said, a certified vessel designed and made by professionals in the compressed gas field should be used.

There may be scuba tanks of that size available, and if you use one, use only fittings and regulators designed for use with it.

I personally do not trust aluminum for pressure vessels at all, but especially not ones at high pressures.

You have had much good advice by previous posters – please take the advice and be safe.

JD

[blowlampParticipant @blowlamp]

So a tube of 20mm internal diameter with a 5 mm wall thickness 600mm long?

Martin.

[Chris TriceParticipant @christrice43267]

Having watched a documentary about the Comet two days ago and how the aluminium fuselage fatigue ruptured after repeated pressurization cycles, instinctively, I'd say ali wouldn't be my first choice at those sorts of PSI. It might work but is it worth the risk?

[steveteeParticipant @stevetee]

Citroen Cars run aluminium cast suspension cylinders, the normal running pressure of the system is 62 bar. When the car is lifted into the high position the full system pressure is applied to the hydraulic cylinders. I know 62 bar is not 1000psi, but the principle is there. The cylinders have a threaded end and the suspension spheres screw on the end , about 30mm, it's a fine thread. failures are unknown.

Mr T

[SiddleyParticipant @siddley]

Is there a really compelling reason it has to be aluminium ? Precharged pneumatic air rifles have reservoirs much the same length and OD you specify and are safe to about 250 bar depending on the model. Many manufacturers sell the reservoirs as spare parts. I'd just buy one of those assuming them being made of steel isn't an issue.

[SpringbokParticipant @springbok]

Well if you do go ahead I hope that you live in a different side of the country from me

Please listen to all the advice given.
Have a safe and pleasant Christmas
Bob

[Nicholas FarrParticipant @nicholasfarr14254]

Hi Mark, 1000 psi is serious pressure and you would not want to be any where near a receiver with that amount of pressure in it should it fail. The threaded ends that you suggest would have a thinner wall thickness and it would be this thickness that you would have to consider in any calculations. All air receivers that I have seen are reduced down or have smaller bush welded in where any threaded portion is.

As others have said, it would be better to obtain a commercially made and certificated receiver for that kind of pressure whatever metal it is made of, especially if it is used in puplic or around any one else.

Regards Nick.

[TerrydParticipant @terryd72465]

I once worked at a large engineering company that designed and made large stainless steel pressure vessels including some for the nuclear industry. there are all sorts of parameters that you probably haven't even dreamed of. An important one is that at the pressure you are proposing the tube will expand in diameter like a balloon. however end plugs will not so the threads will have much less engagement and will possibly blow out. Hence any thread sould be on the outside and caps fitted.

As has been mentioned that is also the problem of failure due the fatigue stresses caused by the cycling of the pressure. It will not give a warning before it fails.

Whereabouts in the country are you? I need to know so that I can avoid it for when the inevitable takes place. The Mayans had nothing compared to this idea.

Seasons greetings

Terry

[Mark P.Participant @markp]

Thanks for the replies,think I will modify the design and use seamless stainless instead! Mike scuba cylinders are charged to 2500-3000 PSI.

Thanks for the replies. Mark P.

[Jens Eirik Skogstad 1Participant @jenseirikskogstad1]

Use waterpressure first with 1.5 x pressure to be sure there is no leakage in more than 20 -30 minutes.

[Ady1Participant @ady1]

Use waterpressure first with 1.5 x pressure to be sure there is no leakage in more than 20 -30 minutes

——–

yup

If you do make your own, test it with water

Air expands like a tnt explosion if you get a breach, water does not

[Ian S CParticipant @iansc]

I'd be wary of any threaded pars of the tube regardless of what metal is used, it will form a stress consentrator, and could be a starting point for a crack. I would say that the 5 mm wall thickness you said for aluminium would be the minimum that I would suggest for stainless. With regard to Citroen, I wonder how many million Francs were spent on the design of their cylinders. Ian S C

[Anonymous]

The oxygen cylinder in one of my two seat gliders was aluminium. Fully charged pressure was about 2000psi. All the cylinders I use (oxygen, acetylene, argon) have bosses on the end with threads in them.

Regards,

Andrew

[ron grimshawParticipant @rongrimshaw76129]

Hi

Not sure if this will help, PCP air rifles use aluminium tubes and can be filled to 2000 psi.

[shaun hillParticipant @shaunhill88399]

A 30mm od x 5mm wall aluminium tube providing its a quality seamless tube would hold 1000psi no problem, make sure your ends are threaded properly. Many modern pre charged pneumatic air rifles are made using aluminium cylinders which i can assure you, some are not 5mm thick, which are designed to work at 3000psi and are tested to 4500 psi, Personally i would use a steel or titaniun cylinder. The vast amount of alloy cylinders on pcp air rifles, manufactures reccomend to replace them after 10 years. The only safe way is to test your cylinder when you have made it, test it to a third above your working pressure, you can use a modified grease gun to hydrostatically test your cylinder.

[blowlampParticipant @blowlamp]

I'd be interested in a simple comparison of the material stresses between this part and the cylindrical section of, say, a 4" diameter model boiler running at 100ps with usual gauge materials.

Anyone feel suitably qualified to have a bash?

Martin.

[Clive HartlandParticipant @clivehartland94829]

Beware stainless steel, my son is a deep water engineer on boats and one day he had just left the engine room and a stainless steel elbow in the 600lb high pressure air system exploded filling the engine room with shrapnel !

Investigation could not find a quality control/origin of the items fitted and the whole system had to be changed. A similar thing happened with a stainless steel hook that was used to secure a door and it snapped, it was rated at 7tons. It showed crystaline fracture.

From that I doubt I would ever use stainless steel in that sort of situation.

The only way is as I said earlier to use a forged/shaped cylinder but certainly not 30mm in dia. in the length quoted. The example of the suspension on a car is with the spheres is that they act as reservours and hold pressure to activate the system.

Here is a factual story, The M109, 155mm Howitzer has hydraulic traverse and elevation of the gun and turret. It was found that the gun and turret sitting on a 7 degree slope could not be traversed up the slope as the pressure was 700lbs in the lines.

The makers were quick to modify and we had to fit the new system at 1500lb and it had a hydraulic reservour 9" dia and 18" long made of 10mm steel wall thickness. All new pipework and new fittings all over to accomodate the higher pressure.

clive

[SpringbokParticipant @springbok]

Well one of my sales managers had a company citroen and it caught fire, the fire brigade was more woried about the cylenders on the suspension than anything else. he was told they could go off like bombs. Could please try your experiments on a deserted island.

Bob

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