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Berlin AquaDom explosion - what went wrong?
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EPAIII:
The coolant may have been the problem. I once sprayed a mechanical, multi-button switch assembly with a tuner cleaner because the contacts were dirty. It had clear plastic buttons on metal fingers and the spray apparently got up in those recesses. For the next several days almost every time someone pressed one of the buttons, it fell off in pieces. The tuner cleaner wicked into the stress cracks and lubricated them into progressing far faster than they were without it.

I had to buy and replace all the buttons. After that I removed the buttons before spraying the switch assembly.

So yes, some plastics can exhibit very rapid cracking when cleaners are used.




--- Quote from: coppercone2 on December 16, 2022, 05:15:53 pm ---I drilled a hole on the edge of a acrylic and tightened it with a screw, 1 month later it cracked. I used a acrylic drill bit too and drilled with coolant. Very sensitive material

--- End quote ---
HighVoltage:
When studying at the Hamburg university, we had a little project, researching gases.
For this project I built a small pressure chamber
Acrylic tube, about 50mm in diameter and 50 mm long and 10mm wall thickness
The ends were closed with aluminum plates

At about 10 bar pressure, this acrylic chamber bursted into many pieces, even killing a light tube, 2 m above the chamber!
We were extremely lucky that nobody was near the chamber at the time.

Afterwards we used polycarbonate tubing in the same dimensions, tested it to much higher pressure and never had a problem again.

So, I learned early on, to never use acrylic plastic for critical applications.

That is why I am so much surprised to read that they used acrylic plastic for this AquaDom
But maybe its is a special acrylic.
The final investigation report will probably be very interesting.

 

pcprogrammer:
What surprised me was that the tank was constructed from separate parts of the curved acrylic, and that they managed to stick them together without visible seams.

For the inner cylinder not to big a problem with a compressing force on it, but the outer cylinder must have had a lot of strain on these seams due to the outward pushing force. Can't but wonder how they did this bonding and make it so strong. It did hold for 19 years.
Siwastaja:

--- Quote from: pcprogrammer on December 17, 2022, 10:43:56 am ---What surprised me was that the tank was constructed from separate parts of the curved acrylic, and that they managed to stick them together without visible seams.

--- End quote ---

With a suitable glue with refractive index close to that of acrylic, the seams just disappear completely from sight.

Acrylic enables visually stunning structures, clearly this is why they used it. I can confirm the chemical compatibility is total crap. Even just something like water with the usual contaminants in it can cause almost invisible micro cracking.

But polycarbonate does not look as nice. It has that smoky or purple tint in it, and a little bit of haziness, too.
tom66:
The bonding is claimed to be proprietary, but it's a reasonable guess that it's a case of polishing the mating surfaces and then using an adhesive of some kind, there are only so many ways to solve this problem. I wonder if it is possible that at the surface exposed to the water that adhesive could progressively allow water into the joint, which eventually forced two halves apart, especially if the low temperatures of the hotel lobby allowed for some kind of expansion-contraction against the 26C tank water.   

The problem with this explanation is this might lead to the tank bursting, but I'd expect to see some complete parts of the tank assembly either where the tank was, or at least on the floor adjacent.  That would be even more dangerous than the situation we've seen, because a ten-tonne piece of acyrlic crashing through the adjacent hotel block would probably tear a hole in some of the residences. We didn't see that - the pieces of acrylic are, at most, the size of a large sofa in the lobby.  Maybe that suggests that the bonding is not simply an adhesive but a plastic welding process, creating effectively a single continuous sheet of acrylic.  In which case, the only failure mechanism available is catastrophic.

I'm also surprised we don't see much of the central tube remaining, as I would have thought that would be safe from a failure of the outer walls.  Imagine if someone had been in that elevator shaft when the main tank burst.  That could have been deadly.
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