Note that extruded tubing may not develop a very high hoop strength due to the
axial alignment of grain boundaries during the forming process.
Build a test motor case and run a hydrostatic test. You should be doing this on
homebrew motor cases anyway. A hydro test is easy and cheap enough to perform,
use a grease gun filled with a heavy sugar syrup instead of grease. This will
supply several thousand PSI and is a lot easier to clean up than actual grease.
You'll need to put a couple tee fittings in the supply line: one to attach a
pressure gage and one for a valve. Fill the casing with water and make sure to
purge all the air out of the system before closing the valve and starting to
pressurize.
It is dangerous to test with air in the system. When a failure begins (say the
case begins to stretch just before a tear in the wall begins), as soon as the
volume increases with a liquid filled volume, the pressure immediately drops.
Water can't expand to maintain the pressure, unlike air. This has a practical
side as well, when you can see the how a failure starts, it is much easier to
devise a solution.
Ad Astra,
Ray On Sunday, April 26, 2020, 09:38:50 AM MDT, Nikolai
Nielsen <nielsen.nikolai86@xxxxxxxxx> wrote:
i want to get back into rocketry and ive got a 2m pole of extruded aluminium
pipe that used to be a tv antenna pole. I want to take a piece to make a motor
casing but have no way to work out the pressure rating and cant access Richards
excel thing for that. can someone help me get an estimation of its pressure
rating? its 38mm OD, 34.5mm ID, 1.5mm wall thicknessmuch appreciated.
Nikolai Nielsen
