N Gas Shelf Life?

[Goodbye710]

For my scuba mask setup, I have a 20 N gas cylinder which has a purity of 99.999%. I've seen it mentioned on the internet the shelf life is 3 years depending on the quality of the cylinder. Does anybody know how important the expiration date is on the cylinder? How much further out I could reliably use the N. Because of the large tank, I'm more worried about the purity. Any further info would be greatly appreciated.

Here is a quote from the internet
"Over time, the amount of gas in the bottle may diminish or disappear entirely. Time, environment changes, and reactions to other chemicals can all deteriorate the amounts and quality of gas in your cylinder. Gas concentration is also a factor that can change the shelf life of a gas bottle."

 

[Aap]

Uh, I believe you are referring to tank leakage. N2 doesn't decompose in a meaningful way. As long as the cylinder is sealed, it will stay N2

 

[AJ95]

N2 gas doesn't decompose as @Aap said, as long as your tank is well sealed and you check the pressure before using it, you should be all good

 

[Deleted member 17949]

No real reactions to worry about with N. The canister may leak over time depending on it's quality and wear but you don't really have to worry about N 'going off' over short periods of time.

 

[JustLosingMyself]

A few million years?
It depends on the quality of the canister. Eventually the seals will degrade and cause leakage, that that takes a few years.

 

[BipolarGuy]

Nitrogen is stable.

 

[Goodbye710]

Thanks everyone. I was always under the assumption that N gas is stable and could be kept for a very long time. I can only assume the gas manufacturers here in the US are makng a big deal out of the expiration on the non reactive gases like N for legal reasons of the canister failing and probably to collect yearly rental fees on their canisters. It seemed hard to understand a 99.9995 N tank would not be roughly that many years from now that the gas manufacturers were suggesting

Here are some more quotes from the internet here in the US for anyone curious.

Even with the gas being in a sealed container and in a climate-controlled environment, there is still an expiration date that will be met sooner or later. There are essentially two different types of gas that is used in these calibrations. They can be broken down into reactive gases or non-reactive gases. The most common non-reactive gases in calibration bottles are methane (CH4), pentane (C5H12), propane (C4H10), hexane (C6H14), carbon dioxide (CO2), hydrogen and nitrogen

With that being said, the most common reactive calibration gases are hydrogen sulfide (H2S), chlorine (CL2), nitric oxide (NO), nitrogen dioxide (NO2) and ammonia (NH3). Because these gases are more likely to react inside the bottle, the time frame on these are around 6-12 months.

A quality gas bottle manufacturing company will produce a cylinder with the smoothest internal walls possible. Even though it is at a microscopic level, the smoother the inside of the bottle equals a smaller surface area which helps with reactions in the bottle. Another factor in bottles with rough internal walls is the ability for the rough parts to hide contamination that would have been present on a smooth walled bottle. Over the years, bottle manufacturers have been able to produce smoother and smoother bottles which has led to a longer shelf life of the gases

Some gases can undergo chemical changes during storage that can alter the purity of the gas or compromise the integrity of the cylinder. For these reasons, it is important to abide the manufacturer's recommended shelf life, and to purchase only what will be used within that period.

Hydrostatic testing is required by the DOT for cylinders that are to be transported in commerce. Hydrostatic testing verifies cylinder integrity. Testing is generally required every five or ten years depending on the type of cylinder. Some cylinders require testing every three years. Cylinders should not be kept beyond the expiration of the hydrostatic test date to ensure that cylinders are safe for shipment and can be returned to the manufacturer. For example, hydrogen cylinders can become embrittled over time. Cylinders should also be visually inspected on a regular basis for signs of corrosion, cylinder fatigue, and valve problems.

 

[Greenberg]

Assuming you have a secure and undamaged cylinder valve attached to your container, your N2 will remain compressed and will outlast your and my FULL lifetimes. Just ensure that the cylinder valve does not get knocked by anything hard. You will be okay.