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I nested my 110g gas canister inside my stainless steel mug for a hike. I used it about halfway through for lunch, and when I was done put it back in the way I had packed it (upside down). Now it is stuck.

My guess is that the canister was at the cooler outside temperature, but the mug had expanded during the cooking. After I put the canister back inside the mug, the mug shrank around it.

The threaded connection for the gas canister is facing top-down in the mug.

How can I safely get the stuck gas canister out of the steel mug? Any ideas?

Loduwijk
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Michael
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    Was the mug designed to be able to hold a 110g canister? If yes, why would it have been so snug that the canister is now stuck? If no, how did you insert the canister without issue and then remove it in the field effortlessly in the first place? – Gabriel Dec 12 '19 at 15:39
  • Theoretically you now have a gas canister protector in the form of your mug. Unless the mug has sentimental value you could leave it there until the canister is empty. – speciesUnknown Dec 13 '19 at 10:13

6 Answers6

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Soak the mug in a sink of hot water to warm it up quickly. Be prepared to pry the gas cartridge out quickly, perhaps using small screwdrivers or needle nose pliers. The thermal mass of the gas in the cartridge will help slow it heating. Some shaking may help.

Then, don’t do that again;)!

Jon Custer
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  • It might (very unsure about this) also be possible to cool the canister and have it shrink using some ice or snow. – bob1 Dec 10 '19 at 09:16
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    @bob1 Not really. The proposed answer relies on heating up the mug quickly while the canister stays cool (because it is thicker metal and full of gas). There is no way to quickly cool the canister while leaving the mug warm. – Martin Bonner supports Monica Dec 10 '19 at 14:13
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    It helps if you cool everything before starting to heat the mug - then there's more thermal difference between the two. Heating the outer part (the mug) is still required (and use hot water, to avoid spots of over-heating). – Toby Speight Dec 10 '19 at 15:30
  • There is also a chance that the canister (in particular the gas) getting warmer and expanding is actually the issue rather than the mug cooling down. Cooling down the gas in the can will lower the pressure inside and sort of suck the sides in slightly and depending on the gas canister could be a more pronounced effect than the expansion/contraction of your mug due to heat. you might not need to warm it up if you stick it somewhere cold like the fridge over night. (and if that doesn't work warming it up slowly from there in a water bath is a great starting point like @TobySpeight said – J.Doe Dec 10 '19 at 16:40
  • @J.Doe I think this is extremely unlikely, a canister that can measurably deform due to the pressure of the gas changing by a few percent is unlikely to be a canister suitable for holding flammable gases. Thermal expansion of solids, on the other hand, is guaranteed – llama Dec 10 '19 at 17:24
  • Do both: Put the whole thing in the freezer for a few hours, then put the mug in hot water. – spuck Dec 10 '19 at 18:26
  • I would not put it in the freezer, just make sure it is cool. Then stand the mug in a bowl and pour enough hot water into the bowl to heat the mug but not the cylinder. After a minute or so, remove and turn upside down. – Weather Vane Dec 10 '19 at 20:43
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    @MartinBonnersupportsMonica: If the canister still contains compressed gas which can be vented quickly, the rapid expansion of the gas will cause it to cool quickly. (You may have noticed this with compressed air canisters, or CO2 cartridges for paintball guns or soda siphons.) Of course, you can only do this once, and it may not be a big enough effect depending on how much gas is present. – Michael Seifert Dec 10 '19 at 20:50
  • @MichaelSeifert I don't think that would work. The canister will (obviously) cool down, but it will cool the mug too. – Martin Bonner supports Monica Dec 10 '19 at 21:16
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    Oh, I could think of a way of cooling a gas canister quick ... vent some gas! – rackandboneman Dec 10 '19 at 21:25
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    "Then, don’t do that again;)!" Hang on! Repeatability is essential for scientific discovery... – Don Branson Dec 10 '19 at 21:34
  • @MartinBonnersupportsMonica: Heating the mug would also heat the canister, just like cooling the canister would cool the mug. The trick is to heat the outer object or cool the inner one before significant heat is transmitted to the other object. – Michael Seifert Dec 10 '19 at 22:03
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    If the exposed base of the cylinder has a hollow in it, as mine all do, filling that with crushed ice will slow the rate at which the cylinder warms and expands as you heat the mug. I'd start with everything as cold as reasonable, and use water as hot as reasonable, where reasonable is taken to be the range of storage conditions for the gas cylinder (this is cautious, deliberately) – Chris H Dec 11 '19 at 15:32
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    Venting gas would cool the canister, but since "The threaded connection for the gas canister is facing top-down in the mug" it would require either puncturing the base of the canister, or making a hole in the base of the mug. Neither is an ideal solution. – armb Dec 12 '19 at 10:57
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The coefficient of expansion of mild steel is about 12. The coefficient of expansion of 304 stainless steel is about 17. This means the cup expands more with heat than the cannister, so warming the whole assembly should loosen it.

If it was a porcelain, glass, stoneware or other pottery cup, the advice would be the other way around. Coefficient for porcelain is about 4 and of regular pottery is about 5.

Use of lubricant such as vegetable oil is also a great idea.

Ben
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Put a few drops of oil into the mug where it meets the canister. If the oil can seep past there, into the mug, add as much oil as possible. See whether you can twist the canister out. If not: Chill the whole assembly. Get tools to handle the mug and canister. Heat the mug in very hot water, and pry it out. Twist as you pry.

ElHombre55
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How did this happen?

Yes, the mug was warm. But also, the gas canister got colder. It is stored in liquid form, but you use it in gaseous form. That means as you use it, the liquid gas must boil. To transition from liquid to gaseous state, the liquid gas must absorb heat energy equal to its latent heat of vaporization. It steals that energy by chilling (taking heat from) the remaining liquid and container. Quite colder; you can often see a "frost line" at the liquid level.

(If you're wondering, yes, this tech can be used to make air conditioners. That’s how they work.)

Then, once nestled into the mug, the gas canister warmed up to ambient.

Getting it loose

Start with the whole assembly in the freezer. Give it 6 hours for the liquid gas to get quite cold. Then, pop the mug quickly into the warmest water you can bear. The mug will heat up quickly and expand. The liquid gas is a substantial thermal mass that will make the canister take longer to warm up. You should have a short window of opportunity to separate it.

If not, try again. Just don't handle it in a way that would make it worse!

Harper - Reinstate Monica
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Duct tape a loop of twine or a shoe lace to the visible face of the canister. Then pull the canister out.

MTA
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You can use hot glue sticks to pull it out. Warm a couple of glue sticks from one end and stick to the visible area of the canister. Let it cool down. Now the glue sticks will act as a handle to the can. You can pull the can out slowly. If glue gets removed, try again a couple of times. You can also use this method along with putting the mug in hot water for a few moments.

Search for "hot glue dent puller" videos on youtube for more information.

user296526
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