GTA
All Springer/NP/PCP Air Gun Discussion General => Machine Shop Talk & AG Parts Machining => Engineering- Research & Development => Topic started by: huklbery on January 18, 2013, 06:12:23 PM
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Hi folks
What would the wall thickness in thousands be for 3,000psi for 3x over burst or fail?
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It would depend on the diameter, not just the wall thickness.... For 3000 psi MSWP at 3:1 safety margin (9000 psi to yield) on 6061-T6 tubing, you would need about a 0.092" wall on a 1" OD, but 0.184" wall on a 2" OD....
Bob
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Thanks Bob, glad I asked as diameter being a variable hadn't occurred to me. I was looking to make a small vessel out of solid stock and I'll use an 1/8" then as a minimum.
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Have a look at Schedule 40 6061-T3 tubing. Very reasonably priced and should work for what you are trying to do up to about 1.5" if my numbers came out right.
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Here is a calculator that you can use.
http://www.engineersedge.com/calculators/shell_internal_pres_pop.htm (http://www.engineersedge.com/calculators/shell_internal_pres_pop.htm)
Set the value for joint efficiency to "one" because you don't have any welded joints. To get your 3 to 1 safety factor you can either use 3 x the working pressure, or set the allowable stress to 1/3 of the yield strength of the metal.
6061T6 is normally speced at about 40,000 psi yield, and 45,000 tensile.
Also consider 2024T3 (50,000 & 70,000) and 7075T6 (60,000 & 67,000). They are more expensive but might be worth it depending on the application.
Lloyd-ss
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Something to consider when choosing a material. Yield v.s. tensile strength. The further apart these to are from each other the more likely you are to have a soft failure v.s. an explosive failure. Soft failures result in the material expanding beyond what the seals can cover and all the air passes to atmosphere. Spooky, YES. Hazardous, YES. Life threatening, Typically, Much less likely.
Bill
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Something to consider when choosing a material. Yield v.s. tensile strength. The further apart these to are from each other the more likely you are to have a soft failure v.s. an explosive failure. Soft failures result in the material expanding beyond what the seals can cover and all the air passes to atmosphere. Spooky, YES. Hazardous, YES. Life threatening, Typically, Much less likely.
Bill
Yup, with an outright sudden failure likely Taking your eye out :o
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I'm in the process of making my own PCP, which is far from being finished, but I have every design detail worked out. When I was younger I used to play with model rockets and even make them, I used a simple XLS sheet put together by a rocket specialist named Richard Nakka used to calculate the maximum pressure that a rocket casing can withstand before bursting and you get to put in the design safty factor, tube OD and ID material shear strength and elastic limits.
I find it to be very accurate and gives numbers that are very close to other calculators, the main reason I like it is because it is super easy to use. Here is a link for the sheet:
http://www.nakka-rocketry.net/soft/casing.xls (http://www.nakka-rocketry.net/soft/casing.xls)
I hope you find this useful.
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I'm in the process of making my own PCP, which is far from being finished, but I have every design detail worked out. When I was younger I used to play with model rockets and even make them, I used a simple XLS sheet put together by a rocket specialist named Richard Nakka used to calculate the maximum pressure that a rocket casing can withstand before bursting and you get to put in the design safty factor, tube OD and ID material shear strength and elastic limits.
I find it to be very accurate and gives numbers that are very close to other calculators, the main reason I like it is because it is super easy to use. Here is a link for the sheet:
http://www.nakka-rocketry.net/soft/casing.xls (http://www.nakka-rocketry.net/soft/casing.xls)
I hope you find this useful.
David,
Thanks for that link, and I must agree that the spreadsheet is nicely done.
Small world, 'cause I already had a link to another of nakka's projects about building a strain gauge and in particular the amplifier circuitry for it. He was a pretty prolific fellow.
Lloyd-ss
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Here is a calculator that you can use.
http://www.engineersedge.com/calculators/shell_internal_pres_pop.htm (http://www.engineersedge.com/calculators/shell_internal_pres_pop.htm)
Set the value for joint efficiency to "one" because you don't have any welded joints. To get your 3 to 1 safety factor you can either use 3 x the working pressure, or set the allowable stress to 1/3 of the yield strength of the metal.
6061T6 is normally speced at about 40,000 psi yield, and 45,000 tensile.
Also consider 2024T3 (50,000 & 70,000) and 7075T6 (60,000 & 67,000). They are more expensive but might be worth it depending on the application.
Lloyd-ss
I just bought 1.25 2024 tube with .095 wall ,is this enough for 2500 psi?.I'm building a light weight mrod rifle. Thanks
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Here is a calculator that you can use.
http://www.engineersedge.com/calculators/shell_internal_pres_pop.htm (http://www.engineersedge.com/calculators/shell_internal_pres_pop.htm)
Set the value for joint efficiency to "one" because you don't have any welded joints. To get your 3 to 1 safety factor you can either use 3 x the working pressure, or set the allowable stress to 1/3 of the yield strength of the metal.
6061T6 is normally speced at about 40,000 psi yield, and 45,000 tensile.
Also consider 2024T3 (50,000 & 70,000) and 7075T6 (60,000 & 67,000). They are more expensive but might be worth it depending on the application.
Lloyd-ss
I just bought 1.25 2024 tube with .095 wall ,is this enough for 2500 psi?.I'm building a light weight mrod rifle. Thanks
Milo,
The calculations work out ok at 2500 psi fill.
Using a yield strength of 50ksi, with a 2500psi fill, you have a 3.0 safety factor, which is the S.F. cut-off point that I use. I know you said 2500 max fill, but just FYI, at 3000 psi, you have a 2.5 safety factor, which is not adequate for everyday operation IMHO, but I think the 2.5 is ok in the unlikely event of a one-time overfill, but that is all.
I also checked the thread strength, assuming you are sticking with the 1-1/8-20 threads that are in the M-rod. For a failure at the thread root of the tube, in other words the actual end of the tube blowing off, you have a 5 to 1 safety factor.
If you use the same length of thread engagement as in the stock M-rod set up, you have a S.F. for the plug blowing out the end of the tube of over 5 to 1.
Just for ref, when I have used 1.25 O.D. 2024, I have gone with the .125 wall, because (1) it gives a 3.3 safety factor at 3k and 2.9 at 3.5k (just in case someone gets careless), and (2) it is the next thickness available above .095.
Overall, I think you are ok, but that is just my opinion.
Lloyd-ss
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Thanks,loyds I'm gonna use cross pins for the end plug.