Implosion Risk Assesment

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Grasshopper

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Reading threads concerned with the risk of implosion of a carboy under vacuum, most recently the threads on vacuum degassing, I am left with the impression that some people may not be thinking about this risk correctly. Specifically, some comments suggest that implosion risk can be significantly reduced by decreasing the vacuum from 25 inches of Hg to 20 inches and that the risk can be further reduced by pulling vacuum only on a carboy full to the shoulder with liquid. With the caveat that I might not be looking at this correctly either, let me offer my thoughts.

It is not the vacuum on the inside of the carboy that can cause failure but the higher pressure on the outside pushing in. The driving force for failure is the differential pressure across the walls (the delta P). For ease of calculation, I am going to approximate the atmospheric pressure at 15 psi and full vacuum at 30 inches of Hg in construction of the following table.

.....Vacuum.............Inside Pressure............Delta P
.... 30 (in. Hg)........... 0 (psi).................. 15(psi)
.... 25 ..................... 2.5 ..................... 12.5
.... 20 ..................... 5 ........................ 10

Thus we see that the difference in force across the walls of the carboy from 25 to 20 inches vacuum is not that large, 12.5 psi vs. 10 psi and that there is not all that much difference between full vacuum and 20 inches (15 vs. 10). Thus, if there is a significant risk of implosion at full vacuum, we shouldn’t feel all that comfortable at 20 inches. Unless we know from experimental data or reliable calculations what the failure point is likely to be, we really have no idea how comfortable/uncomfortable we should be. If the failure point turns out to be 100 psi then I would likely be comfortable even at full vacuum but if it turns out to be 20 psi, then I am going to be uncomfortable even at 20 inches knowing that flaws, scratches etc. will reduce the fail point. Personally, I think that the failure point is higher rather than lower given the lack of reports of carboy implosions on this forum (failures of thin wall demijohns not withstanding) but that is just a guess.

Filling the carboy with liquid may reduce the consequences of implosion (see below) but doesn’t change the probability of failure all that much. The increase in pressure at the bottom of a full carboy due to the liquid is about 0.7 psi (about 18 inches of water) so at 20 inches of vacuum, the delta P at the bottom is only reduced from 10 to 9.3 psi.
Implosion implies a failure where the glass shards from the crushing failure caused by excessive external pressure are accelerated to a velocity sufficient to create a flying glass hazard. The liquid in a full carboy will dissipate the energy of the flying glass and eliminate this hazard (if not the hazards associated with spilling 6 gallons of red wine on a white rug).

So how else can we mitigate the hazards of flying glass? In chemistry lab we used to tape the outside of vacuum receivers so that the tape would keep the glass from flying in the event of an implosion. Likewise one could tape the outside of a carboy with duct tape or clear packaging tape. Or one could put the carboy inside a bag or pillow case to stop the flying glass. I use a plastic garbage bag for this which I think is probably sufficient to minimize the hazard. I also keep the carboy in a secondary container to minimize the mess from spilled liquid.
Others may have better methods.
 
Grasshopper, lots of great data there. Some I understand and other I don't even try to. I like what you said about why a full carboy is safer than a partially filled one if it did implode. With all the talk out there for years about the possibility of an implosion, I have yet to hear of an actual case of a carboy imploding that was of a sound state.
 
Runningwolf, an implosion is caused by the higher pressure on the outside pushing on the glass and causing it to break. The broken glass starts off being pushed inward. If the carboy is empty, it encounters little resistance and continues to fly off past the other side of the carboy (or where the carboy was) and becomes shrapnel. If the carboy is full of liquid, the glass is slowed down and doesn't make it all the way to the other side. Think how much easier it is to throw something through air as opposed to through water. At least this is my thinking on the subject as I have no direct experience (and hope never to have any).

Does this help?

I haven't heard of any failed carboys either. I hope anybody who has experienced such a failure will pipe up and let us know the specifics. (again demijohns don't count as they are much weaker vessels).
 
Sorry I must not of worded my post good enough. The part you just explained is the part I clearly understand. Thanks for reexplaining it though as Im sure it will help others. Great job!
 
You've got to love retired engineers that make wine! I don't fit that category, I'm not retired!
 
I have three questions. Has anybody on this forum broken a carboy under vacuum? Has anybody on this forum been nearly injured, or injured, by an imploding carboy? To anyone who has imploded a carboy, can you please describe what you saw?
 
As long as the carboy is full you have noting to worry about. If the carboy is empty and you pull a vacuum on it you might want to wear PPE......
 
As long as the carboy is full you have noting to worry about. If the carboy is empty and you pull a vacuum on it you might want to wear PPE......

Are you not pulling a vacuum on an empty carboy every time you rack with the Allinone? Just curious, I have had no problems so far
 
I don't use an Allinone so can't comment. But I do use a vacuum pump to filter from a full to an empty. In that case that vacuum is distributed across the entire system and NOT a single empty carboy. BIG difference.
 
I don't use an Allinone so can't comment. But I do use a vacuum pump to filter from a full to an empty. In that case that vacuum is distributed across the entire system and NOT a single empty carboy. BIG difference.

Yes the Allinone is doing the same thing as ibglowin explained. The Allinone is designed to pull max of 22'' in hg - but it will probably never reach it due to the LPM of flow it produces and the CO2 being released causing the vacuum pressure to stabilize or increase slowly. This process has been proven by thousands of carboys since it came out, several years ago- without any incidents.

Prior to starting the Allinone I did my own research and development on carboy implosions. I personally have mentioned in previous thread a while back that I tried to push the limits of a carboy and boil water using a carboy that was immersed in warm water (double broiler – otherwise) The carboy was approx ¾ full and the water temp inside was at 120 F – the vacuum pressure was a solid 29.+ in hg, and it was shaking violently for at least 4 hours and I redid the same test for several more times to make sure that a carboy can take those vacuum specs without any issues. All my documentations were recorded and witnessed.

I believe if a carboy would break under vacuum it would not fly apart as some think – as soon as a crack starts the vacuum would then decrease suddenly.

Take for instance a light bulb is under vacuum correct ?? When you break a light bulb does glass go flying everywhere ? no it implodes within itself.
 
it would be neat to emplode one just to see where the failure point is

I agree - I could not do it !! I had one of the most powerfull AC vacuum pumps while doing this test.

Now if you would tap on it while under vacuum - that is a different story, or take it from extreme temperature change.

Now lets say if you had a carboy outside in your garage at 50 F and you put a determined amount of vacuum on it - could it possibly break or implode due to temperature change ???
 
Thig said:
Are you not pulling a vacuum on an empty carboy every time you rack with the Allinone? Just curious, I have had no problems so far

When racking, you would need an air path into the carboy to allow the liquid to leave. You with that said, there will be no vacuum during the racking process.

From the earlier comments: when degassing, with the carboy full, the area exposed to vacuum is small. Remember: force=pressure x area. So lets assume that the neck has an area of 3 sq in and full vacuum is 15psi. The resulting force is 45 lbs. With the carboy empty the area is 115 sq in and the resulting force is 1725 lbs. Big difference.

Note: liquid is incompressible, so it reinforces the glass.
 
Glass carboys are pretty darn robust. It is difficult for them to implode. As a chemist I have used plenty of glass containers under high vacuum and have seen my share of implosions. Most of the time the implosions were the result of a weakened area of the glass. A tiny star crack that you might not even see with the visible eye can be a problem. A tiny scratch in the wrong place on a glass container can weaken it. So, one of the things to be very careful of is to make sure you do not ding or scratch your carboys. I think they are thick enough that we should never see a problem with implosion, but I wouldn't want to push it.

Also, the shape of the container has a lot to do with it's strength. A round shape is ideal and one of the strongest containers for vacuum. Carboys are, of course, not round. But they do have rounded edges, not 90 degree angles.
 
When racking, you would need an air path into the carboy to allow the liquid to leave. You with that said, there will be no vacuum during the racking process.


Note: liquid is incompressible, so it reinforces the glass.

Not sure where you are going here ???
When racking with vacuum - you will always have
Vacuum in the receiving Carboy
 
I think novalou means that during the racking process, the wine is constantly flowing ino the carboy to replace the air pulled out by the pump. Although there is still vacuum in the carboy, it will not be as strong as just pulling straight vacuum to degas. There is probably some equilibrium reached depending on the flow rate of the pump compared to the flow rate of the racking hose and canes but the math is way over my head.

A while back I bought a bunch of Mexican carboys off Craigslist. When I got them home and cleaned, I noticed one of them had a very large manufacturing defect in the form of a deep crack along one of the vertical seams. I figured it was garbage so I put it under 23inHg expecting to see a show but I got nothing. I even tapped the crack with a screw driver under vacuum... nothing. I still don't think it's safe to use that particular carboy but it gave me greater confidence in the vacuum process.
 
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I stated in another post, and posted pics of the problem I had with a new batch of Chinese carboys. One of them cracked when I had just started up my AIP during a racking. I was standing right beside when it cracked just like if you were on a lake and heard the ice crack. I immediately hit the vacumn release and carefully placed the empty carboy into a box to take to the dumpster. I attribute this to the batch of carboys I bought. Several of them were defective.
I no longer handle carboys unless they go in a milk crate first. I also will begin to "tape" em up. As Ben used to say, a stitch in time saves nine.
 
I think for all intents and purposes, we should lump the new breed of Chinese carboys with the demijohns when it comes to vacuum durability.

No offense to any demijohn users out there.
 

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