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All Springer/NP/PCP Air Gun Discussion General > "Bob and Lloyds Workshop"

An airtube question for Bob-4130 CroMoly tube from Aircraft Spruce...

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JuryRigger:
Bob,
Got a question regarding your thoughts on the 4130 CroMoly from Aircraft Spruce...
I had saved a snippet (unfortunately no ability to reference the quote) from a post of yours years back where you said: "I used the 1" OD x .065 on my Hayabusa, it has a yield pressure of 9,400 PSI and a burst rating of 14,500 PSI..."

Aircraft Spruce currently lists their tubing at 90,000 PSI ultimate strength; and I'm having a difficult time reproducing a calculation that makes me feel comfortable with using that particular tubing for a 3KSI fill (Barlow's)-at least on the yield; but I've not been able to find an official figure from Aircraft Spruce on their tubing's yield strength; and have been using one-third of the UTS (30,000 PSI) for lack of a more accurate figure... A web search shows it to be 63,100 PSI, but I'm not entirely trusting of that figure, any more than I'm sure of mine (although I at least know mine is way yonder underestimated)...
What figure did you use for the yield strength for your calculations?...
Thanks in advance,
Jesse

rsterne:
4130 CrMoly is 63Ksi Yield and 97Ksi Tensile.... I use Lloyd's spreadsheet to calculate my yield and burst pressures, as Barlow's is for thin-walled tubes (20:1 or greater, D/t).... At the time I did the first Hayabusa, I probably used Barlow's but used the ID instead of the OD.... Lloyd's calculator, using 63/97 Ksi gives me a yield pressure of 8,700 psi and a burst pressure of 13,400 psi.... Using a 3:1 safety margin to Yield would give a MSWP of 2,900 psi, using 3.5:1 to Burst (which is what I do, providing the Yield is over 2.5:1) gives a MSWP of 3,800 psi.... However, in this case I would use the Yield at 2.5:1, which gives a MSWP of just under 3,500 psi as my limit.... It all comes down to personal choices at that point.... Lloyd and I discussed this at length, and built 2.5:1 to Yield and 3.5:1 to Burst into his calculator....

I use Matweb....  https://www.matweb.com/search/DataSheet.aspx?MatGUID=e1ccebe90cf94502b35c2a4745f63593&ckck=1

Bob

JuryRigger:
Many thanks Bob  :)
Jesse

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