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If I put a strong, sealed container of liquid nitrogen on a table at room temperature, will it always stay cold? Or will it slowly heat up until the canister bursts? Assume it is an extremely strong container made of reinforced materials? I suppose no matter how strong, it will still explode one day. Any idea how long a standard reinforced LNG bottle will last before it explodes?

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The liquid nitrogen will certainly warm up to room temperture, and a high pressure will build up inside the container (I assume, your container provides no thermal isolation). If the container is firmly sealed, it will eventually explode, if the pressure becomes higher than what the container can stand. For example, this happens when you fill liquid nitrogen into a plastic bottle (don't try it out!!!, there is serious risk for your health doing it). However, special tailored containers may stand these high pressures, e.g., special steel containers.

As a rough order of magnitude estimate: at normal pressure, the gas takes roughly 1000 times the volume that the liquid needed. If the volume is kept constant, the pressure will rise roughly by a factor of 1000.

Note that this is a bit handwaving, but suffices for most practical cases. For a more precise description of what is going to happen, you have to consult the phase diagram for nitrogen.

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  • $\begingroup$ Thanks a lot @flaudemus, but what if it is an extremely strong container made of reinforced materials? I suppose no matter how strong, it will still explode one day. For interest sake, any idea how long a reinforced LNG bottle will last before it explodes? $\endgroup$ – Hein Vogel Feb 7 '19 at 11:45
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    $\begingroup$ There are not special steel nitrogen dewars that remain sealed while the liquid nitrogen inside warms up to 1000 atmospheres. At least, not for storing liquid nitrogen. Small dewars are open to air, and are closed only with loose-fitting lids. Larger dewars have a system of pressure-relief valves. $\endgroup$ – rob Feb 7 '19 at 11:48
  • $\begingroup$ As far as I know, natural gas is transported in its liquid state in big container ships across the ocean. The same reasoning would apply there. They do not explode. If such a container would explode 'one day', depends on how the strength of the container degrades over time, and when exactly 'one day' is. The second law of thermodynamics makes sure that indeed, 'one day', the container will at least leak, if not explode. $\endgroup$ – flaudemus Feb 7 '19 at 11:52
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    $\begingroup$ @rob: of course, in practice we do not use such sealed containers in the lab. But the question started with 'If I put a strong, sealed container of liquid nitrogen on a table at room temperature ...'. So we were not asked, how we do things in the lab. $\endgroup$ – flaudemus Feb 7 '19 at 11:54
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    $\begingroup$ @flaudemus, LNG carriers can use the boil off to power the engines, which removes the over-pressure; see en.wikipedia.org/wiki/LNG_carrier#Reliquefaction_and_boil-off $\endgroup$ – Roger Lipscombe Feb 13 '19 at 9:18
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There is no such thing as perfectly isolated cryogenic tank. Some heat will always transfer to the contents. However, cryogenic liquid tanks are not completely sealed. They instead have pressure relief valves. The valve opens when the internal pressure exceeds some upper limit, then closes when the pressure drops below some lower limit. This is the mechanism by which cryogenic liquid tanks (including liquid nitrogen tanks) stay cold.

Suppose a full liquid nitrogen tank is abandoned for decades. What happens over time won't be very exciting. A decade later, the tank pressure will be somewhere between the relief valve's upper and lower pressure limits, the temperature will be very close to ambient, and the mass of nitrogen in the tank will be very small. Almost all of the nitrogen will have boiled off and been vented to the atmosphere.

Now suppose the tank is abandoned and the relief valve fails in the closed position. What happens in the ensuing decades will briefly be exciting. Something will fail, catastrophically. It might be the relief valve, it might be some other valve, or it might be the tank itself. The end result will be an empty tank (or perhaps an empty remnant of a tank).

Finally, let's suppose the tank has no valves and is incredibly strong. For lack of better words, it's made of unobtainium. (But not Thermodynamically Isolated Unobtainium©; that stuff is ridiculously expensive.) After decades of abandonment, the contents of the tank will be at ambient temperature and at a ridiculously high pressure. The contents won't be a liquid (nitrogen's critical temperature is -146.9 °C), but it won't quite be a gas, either. The reactions of a highly pressurized supercritical fluid are somewhere in between those of things we call liquids and things we call gases.

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    $\begingroup$ @HeinVogel: if you think the answer is perfect, then 'accept' it, plse. $\endgroup$ – Gert Feb 7 '19 at 15:12
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    $\begingroup$ Re, "somewhere between [liquid and gas]." I would not say "between," it's more like, "beyond." Think of the line separating liquid from gas as a sheer cliff on the pressure-temperature landscape, As you walk toward the critical point, the height of the cliff becomes less---the physical properties of the phases on either side of the line become more alike. At the critical point, the height of the cliff becomes zero, and in the region beyond (i.e., in the supercritical region) there is no longer any cliff. $\endgroup$ – Solomon Slow Feb 7 '19 at 17:38

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