Developing 10,000psi Extreme pressures *POP* for air gun component testing

[lloyd-ss]

Did we really exceed the yield point of the aluminum tube as calculated    Well, actually, yes we did   

The original tube dia was .999 to 1.000.  I checked the tube with calipers and decided to get the mikes out to check it more carefully.
Both of the ends of the tubes are isolated from the pressure by the o-ring on each end plug, and they did not change size.

The middle of the tube swelled to about  1.0035 to 1.0045    So that is 0.4 percent (less than one half of one percent) permanent deformation.
Yield offset is normally .2 percent, so this is barely, but definitely, into the permanent deformation region.  But the material is behaving exactly as it is supposed to, so I am happy !       If all follows as it is supposed to, the tube wouldn't burst until over 13,000 psi, and I don't know anybody who has that kind of air or nitrogen easily available.
So my opinion is that the 2024T3 aluminum airtubes, when properly designed, manufactured, installed, used, and maintained, are very safe.
Lloyd-ss

[rsterne]

EXCELLENT RESULTS !!!.... It is actually very reassuring that you found some permanent expansion in the diameter, it shows that the material is on spec and that our math is good as well.... Thanks for measuring it up after the test.... I would agree that your tubing choice is a good one for the purpose, in fact for anything running at 3000 psi or below.... just over a 3:1 safety margin to yield....

Bob

[PakProtector]

hey Lloyd,
I have to weigh in on your pressure step-up. You've still got a substantial air spring compressed. I would suggest that for failure testing you use a hydraulic pump on the low pressure side. Something like a Porta-Power's pump...keeps stored energy to a minimum, which IMO is a very good thing whilst running pressure testing.
cheers,
Douglas

[lloyd-ss]

Douglas. We discussed this earlier in the thread, and I have designed the system with  adequate precautions.  i appreciate the concern. But if you can loan me a porta.power,that would be even better! LOL
Lloyd-ss

[PakProtector]

Douglas. We discussed this earlier in the thread, and I have designed the system with  adequate precautions.  i appreciate the concern. But if you can loan me a porta.power,that would be even better! LOL
Lloyd-ss

On the pump, I'll have to agree with you; they are not easy to come by inexpensively... I'll let you know when I finally find one( which loaning to you might be more productive than keeping it ).
cheers,
Douglas

[lloyd-ss]

The aluminum airtube passed with flying colors at 10,000 psi.  To get it to fail I had to machine the O.D. of the tube down to make the tube wall artificially thin so that it would rupture below 10,000 psi.  And it did fail rather nicely after machining 1/2 the wall thickness away..
Lloyd-ss

[PakProtector]

that was cooool. I was wondering if you would take the wall thickness reduction across the threads or if you'd leave the threads( and o-ring seal ) full and have a wall burst. Nice vid BTW.
cheers,
Douglas

[lloyd-ss]

Douglas, to be perfectly honest, I was not anticipating that failure, and thought I had about 2k more to go before the wall ruptured. But after seeing it and doing the calcs, the thread root was the weak link for sure. When I first saw the failure, I thought the threads pulled out.  The material stretching at the failure line is very easy to see with an eye loupe.  You should have seen the barricade I was behind for that test, LOL.
lloyd-ss

[Bill G]

Lloyd,  I'd say you need an apprentice just to clean up after you on that one.

[Cliff]

Bursting tanks are not your only concern.

Petroleum oil  aspirated into the air is deadly. 

You are talking about  a lot of pressure  which can easily accomplish this.
The reason it is deadly is simple. It coats the alveoli  prevent them from being able to effect a transport of O2 into the blood stream and  the lungs can not clear it in time to prevent death.

[lloyd-ss]

Cliff.
Thanks for the concern and the info. During the recording, i was inside my shp and the test set-up was outside. the video cam was outside too
lloyd. 

[QVTom]

Douglas, to be perfectly honest, I was not anticipating that failure, and thought I had about 2k more to go before the wall ruptured. But after seeing it and doing the calcs, the thread root was the weak link for sure. When I first saw the failure, I thought the threads pulled out.  The material stretching at the failure line is very easy to see with an eye loupe.  You should have seen the barricade I was behind for that test, LOL.
lloyd-ss

The "pop" had more energy than I expected  

With the data you now have, you could calculate the thread root area and see where it failed with respect to the material properties.  This would give an estimation of how the stress concentration (notch sensitivity of the matl) from the national v form thread affects the tensile of the material.  Hard to nail down with one test but a ball park fiddle factor for the threaded area would shed some valuable insight for future designs.

Tom

[lloyd-ss]

Tom, I was planning on doing that but it slipped downward on the to-do list. You pushed it back up, LOL. 
 The hole in the tube is tapped so that it only has one spare thread before the plug jams in the threads, and the failure occurred at the root of that one lone  full thread. The tube is tapped 7/8-24 and I just miked the tap at .880 dia.  The tube mikes at .910 O.D. so that gives .015 wall, or  .0422 sq in.
The plug is sealed on the as-drawn I.D of the tube which is .810 (1" tube with .095 wall, verified) or .5153 sqin.  It looks like the failure occurred at 5,100 psi which is 2628 pounds of force (pardon the significant digits), which calculates out to a stress of about 62,300 psi.  The figures I have been using for 2024T3 are 50ksi yield and 70ksi tensile.  So the 62,300 break seems appropriate for the stress concentrations at the root.  In fact, considering the very thin .015 wall, and the cut thread, I'd say that is quite good.
What do you think?

As an aside, if the tube were full diameter of 1", that would give .1772 sqin, or a loading of 1804 pounds at 3,500 psi air, or a stress of  10,170 psi, or a safety factor of greater than 6 to 1.  I think I can sleep peacefully on that one.
Lloyd-ss

[gene_sc]

Really great work Lloyd. The testing is great for the the advancement of PCP hardware. Amazing that there is aluminum tubing out there that can hold up to these pressures and be lighter than steel.
Gene

[melloroadman]

Lloyd I know that many of the BB makers are using 4130 CM  . How does this compare weight wise as well as ding, dent resistance as well .Marvin

[lloyd-ss]

The CM is a stronger and tougher material, but significantly heavier.  But the 2024-T3 aluminum that I used is a hard, high strength alloyy, that is used in aircraft airframe construction. It might not be as tough as the CM but it is strong and fatigue resistant.

For the 1" tube, I used .095 wall 2024 aluminum , and the safety factors (3 to one and better) allow it to operate at about 3200psi.
A CM tube of the same strength could be about .065 wall.

In comparison,  considering a 16" long tube:
Al .095 wall     CM .065 wall
Al 135cc          CM 156cc
Al .41 lbs        CM .88 lbs

Bottom line is, if you are rough on equipment (dings and bumps), and don't care about the extra weight, use the CM.
If you want the lighter weight, definitely go with the aluminum. I have no concerns about its strength.
Lloyd

[melloroadman]

The CM is a stronger and tougher material, but significantly heavier.  But the 2024-T3 aluminum that I used is a hard, high strength alloyy, that is used in aircraft airframe construction. It might not be as tough as the CM but it is strong and fatigue resistant.

For the 1" tube, I used .095 wall 2024 aluminum , and the safety factors (3 to one and better) allow it to operate at about 3200psi.
A CM tube of the same strength could be about .065 wall.

In comparison,  considering a 16" long tube:
Al .095 wall     CM .065 wall
Al 135cc          CM 156cc
Al .41 lbs        CM .88 lbs

Bottom line is, if you are rough on equipment (dings and bumps), and don't care about the extra weight, use the CM.
If you want the lighter weight, definitely go with the aluminum. I have no concerns about its strength.
Lloyd

Lloyd  Thank you for the info . I do not question the safety of your material or work . You at least take the time to test what you use . Most do not . Just trying to gather knowledge . Some of them blue and some paint so that might be part of the reason for their material choice as well . Marvin

[QVTom]

So the 62,300 break seems appropriate for the stress concentrations at the root.  In fact, considering the very thin .015 wall, and the cut thread, I'd say that is quite good.
What do you think?

Yes, I agree.  Very good.   The added copper content of the 2024 really adds to its toughness. 

How does this compare weight wise as well as ding, dent resistance as well .Marvin

  A hard anodize or nickel will go a long way towards preventing cosmetic damage but hard knocks may leave dents, I wouldn't expect them to compromise the integrity of the tube though.  With in reason of course.

Tom