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For a laugh, a mate and I printed a DIN blanking plug for a SCUBA cylinder yesterday.

It's a 20mm(ish) straight 13tpi 55º profile with specific point radius calculations - but it's a very common gas standard thread.

Anyway. Printed in ABS at 255ºC, 0.2mm height at a fair old clip with 6 layer perimeters, 6 layer top and bottom, 30% honeycomb fill. We were doing it no favours at all.

There was a groove for an o-ring at the top of it which had a few artefacts, I didn't think it would survive long enough for it to matter, so we threw an o-ring in there as it was, wound it into a SCUBA tank which was filled to 150 bar (2200 PSI), put on some safety glasses and gloves and opened the valve.

Nothing happened.

There was a dribble of gas coming out along the thread (I'll happily blame the o-ring seat for that) but none of the expected results:
1. Explosive failure as the 750kg of force on the plug simply sheared the threads and fired the plug at the water tank it was pointed at.
2. Partial failure as layers (there was a central relief tube) separated at some point and blew the end-cap off.
3. Massive fizz fest as the print's porosity let air just bleed through.

None of these things happened. Sprayed with soapy water (a trick we use to find leaks on dive gear) but just the leaky o-ring, the rest of it held tight.

I'm not about to start printing full pressure dive gear as a result, but this is going to take a little time for me to digest I think. All this noise about it being porous, weak, etc has just gotten turned on its head.

I'm impressed. And a little scared by the implications on what is now possible.

Might be cool to clean out the o-ring groove so it doesn't leak, and just let it sit. Cage it so when/if it fails it doesn't shoot something/someone important and just see if it looses pressure after a couple days.

wow that is impressive and unexpected.
I am making 3d parts (not life critical) to be used in seawater upto 200- 300 ft deep, and this is a good sign.
also considering coating with http://www.smooth-on.com/index.php?cPat ... baj3pter00
for an even better seal. what do you think of the coating, might it also help in your application.

With ABS an acetone wash (or steam bath) is enough to close up the gaps and everything.

What blew me away was that, completely raw off the printer, it didn't leak like a sieve and it didn't explode under the pressure.

I have another part (an oxygen cell tester) I'm working on which needs to hold up to 5 bar pressure without appreciable leaking for half an hour. When I get the pressure relieve valve design sorted out, I'm going to be VERY curious to see whether I actually need to machine it out of POM (Delrin) on the 4 axis CNC or whether I can just print it in ABS and be done!

I never would have thought that a 3d printed part could hold pressure.
Your testing is amazing.