3 gallon tank burst test

I tested the LRD-3 Aluminum air tank and it burst at 828 psi (57.1 bar). IMG_0070 3galBurst

Dry Mass: 2.34 kg (5.16 lbm)

OD: 7.271″ (18.47 cm)

Wall thickness: 0.097″ (2.46 mm)

Ultimate strength: 30,204 psi (208.2 MPa)

This ultimate strength is about 10% higher than what I computed for the 5 gallon tank, but still well below the 42 ksi UTS I’ve seen published for 5086-H116. I posted the entirety of the burst test video (burst occurs 2:09) so you can see the tank balloon as it is pressurized. The catalog diameter of the tank is 7″, but I measured a 7.271″ OD after the test; I neglected to measure the tank OD before the test. In retrospect, it worked in my favor that the UTS was lower than expected because my tester and pressure transducer are only good to 1000 psi.

 

 

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4 Responses to 3 gallon tank burst test

  1. Akos says:

    From what I remember, aluminum cant be used for lox service especially at pressure.

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    • arcranda says:

      No, this is incorrect. Armadillo and Masten used aluminum tanks, tubing, and fittings on their vehicles. I’m not sure the specific alloy, but I think Armadillo used 5000 series spheres on their “mod” and “quad” type vehicles and 6000 series sheets welded into tubes for their STIG vehicles. NASA’s Morpheus (a variation of Armadillo’s quads) vehicle also used aluminum spherical tanks and the brilliant white sparks in crash video are aluminum burning. Paul Breed (another NGLLC competitor) experimented with aluminum irrigation tubing as tank material and fired a LOX/alcohol engine with. Shuttle ET, Falcon 9 tanks, Atlas V and Delta IV tanks are all made of an aluminum-lithium alloy. I’ll concede that aluminum doesn’t have the ignition resistance of a nickel alloy like Inconel or Monel, but (properly cleaned) it can definitely be used in oxygen service, especially at the pressures and flow rates amateur rockets use. One more rebuttal, medical oxygen tanks are made of aluminum and contain GOX at much higher pressures than what my proposed LOX tanks would see.

      I genuinely appreciate your comment! My blog doesn’t get much traffic; it’s nice to know somebody is interested enough to share their thoughts.

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  2. Joe says:

    After welding the material is not as strong as the parent material and clearly the tank failed in the weld affected zone. Likely the tank was not post-weld heat treated – if it was there would be a bit more strength, but the welding is still a limiting factor for all practical purposes.

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    • arcranda says:

      Joe, thanks for the input and sorry for my (very!) tardy reply. You’re right, I shouldn’t have compared the UTS I calculated from the burst test to the -H116 UTS. But, I thought the UTS in the HAZ isn’t supposed to be less than the -O condition, which a quick Google says is 32 ksi, so my tank UTS is still suspiciously low.

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