TANK HYDRO TESTING: Hydro testing of our first sample Chicora propellant tank was another learning experience.
Tank is a seamless 6061-T6 aluminum tube, .125" wall thickness, 8" diameter, 16" long, welded to 6061-T6 tank caps with 4043 filler metal.
Working pressure is nominally 500 PSI. Hoped to get to 625 PSI, but weld had hardly any penetration and let go just north of 400 PSI.
Weld was so poor, penetration wise, that the underlying material wasn't torn, just the filler parted.
We'll cut an inch off the ends, chamfer the tube and tank caps, then go for a full penetration weld for round 2.
I weighed the tank full of water before any pressure was applied and measured diameters and lengths.
At 250 PSI, I remeasured, and saw no increase in weight and negligible increases in diameters and lengths.
If at 500 PSI I see no large increases (< 1%?) I'll feel pretty good about the tanks.
I'm surprised the thing held to over 400 psi with just the strength of a thin section of 4043 filler metal holding the pieces together.
I probably shouldn't have made such a big deal to the welders about keeping the heat down into the base metal - there was barely any base metal fusion at all. :-(
Here's an image of our hydrostatic test setup:
The tank sets on a wooden base in the deep sink.
The bottom tank bulkhead is like the top, with a central hole,
which we have plugged with a Swagelok O-ring fitting.
We fill the tank initially from the faucet, then place it on the scales to measure total weight, full of water.
Back in the sink, the wooden base lets us rotate the full tank (37 lbs when full of water) when attaching the upper o-ring fitting.
We drilled an aluminum block and tapped it 1/4" NPT for the fittings: The hydro hose comes in from the left;
a pressure transducer (not used for hydro) is on the right; and a manual ball valve to fill and vent the tank is at the top.
With LOX-8 on the NPT threads, it went together well with no leaks.
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