Exploded CO2 bottle

[Doc Nickel]

is there a requirement to heat treat these cylynders after manufacture, eg percipitation treat or whatever?

-Oh yes. I don't know exactly what kind of heat treating is done, but I recall one spec noting that some 40% of the tank's strength comes from the heat treat. Or to put it another way, the heat-treated tank is 40% stronger than the same tank, annealed.

But then, the same is true for steel tanks as well- maybe not the same ratio, but the material is still definitely heat-treated.

DOT regulations, in fact, require the destruction of any tank that's been exposed to more than X temperature for a given time period, though I can't recall if that spec was 150 or 200 degrees.

Many years ago, a few people were killed trying to fill some SCUBA tanks that the owners had had powder coated. The heat of the baking process annealed the tanks, which then exploded when filled. As noted earlier, the tank wall had become weaker than the burst disc, so the relief couldn't save them.

Personally, I had one customer seriously pissed off with me when I "destroyed"- I drilled a hole- in a tank he'd had powder coated to match his paintball gun. I don't know who did the actual work, but he sent it to me (along with the gun) for assembly and tuning. There was no way I was going to return the tank, knowing, as I did, it was horribly unsafe to use. If I refused to assemble it, he'd have just found some other doofus to do it- or done it himself- and wound up dead or injured for it.

I replaced the tank, but I doubt the customer really knew what I saved him from, and probably never forgave me.

Doc.

[Rich Carlstedt]

Hey doc
Aluminum age hardens by natural occurance.
If those tanks blew after powder coasting, its because they were used immediately.
They should have set them aside for a month, or post treated them at 260 degrees for 24 hours
6061 for example goes from T1 to T 6 after 30 days at room temperature.

Looking at the failure says the bottle was faulty in my opinion.
The straight line up the side, like a zipper suggest a thin spot along the axis of the bottle. It could also have been subjected to a vise like clamp that marked the side , but the failure is not a normal hoop strength loss ?

The tank wall thickness should be miked !

rich

[airsmith282]

thats a big mess , co2 is pretty dangerous stuff ,i been shooting and working on co2 pellet guns for a long time now and co2 runs about 1000 to 1500 psi on average usually closer to 1500 psi , tanks are suppoosed to be hydro tested but perfered to be replaced every 5 years your also supposed to pre chill co2 bolltles before filling them, and keep them away from heat sources, i let a gun sit on the table for about an hour one day it was about 25 C out side and all the seals in my gun just up and blew and that was only a gun using a 12gram bottle , i have to agree as well aluim should not be used for co2 but 12gram carts are steel and just as dangerous , but the aluim is pretty thick walled , if your going to strip down a bottle for reapainting id use something like poly stipper, taking off any kind of ruff surfacing id just go buy a new bottle the surface is supposed to be smooth on thoes bottles, aluim is a bad choice in that any out side heating of the bottle past reccomened will make them swell and blow up like bomb if the safty valve failes and sometimes the valve will fail if its not replaced from time to time as well, the HPA stuff i realy dont like, it runs 3000+ psi and the bottles are no where near the quility , i hav e seen them made from aluim to carbon fiber for paint ball guns and i dont trust the stuff at all expeciially the carbon fiber ,, so iam guessing that this bottle explosion had to be a heat issue and a failer of the safty valve..
anyhow i hope your friend is alright...

[pressurerelief]

Rich, the failure of the cylinder is typical of a pressurized vessel failure. When a railcar goes like that we call it a dance floor. Lays it out nice and flat alot of times. I have a steel cylinder sitting on my bench that has the same type of result straight up the sidewall. The failure was from disassociation of the liquified gas in the cylinder and built up pressure from the hydrogen. Quite common from Hydrogen Fluoride and Hydrogen Bromide. I happened to be standing about 20 deet from the cylinder when it "went" and the only negative was ringing in the ears for hours. The gent closest to it might have had to clean out his drawers.

Airsmith, CO2 has a vapor pressure of approximately 835 psi. It is not and will not be over 1000 psi in your house. Refer to this link.

http://encyclopedia.airliquide.com/E...a.asp?GasID=26

Carbon Fibre cylinders are safe and have a well documented service history. They can withstand thermal cycling to some degree and still pass a hydrotest. If you doubt this look on the back of most firefighters, this is what they wear.

As far as CO2 cylinders Doc has it right and you can overfill a cylinder. I would like at an improper burst disk first and mechanical damage second as a root cause. Aluminum cylinders are prevalent in the market and have a low failure rate. Most of your calibration gas cylinders are aluminum. The DOT regulates these and keeps stats on failures. If they were not safe they would not be approved by engineers far more versed on this subject than I.


We had this same keyboard disagreement about overfilling a propane cylinder on this board. Alot of conflicting information here.

P/R

[Jpfalt]

Doc and Rich,

Precipitation hardened (or age hardened) aluminum has to be solution annealed before it can be rehardened. Solution annealing happens at about 950 deg F. and is immediately quenched in water or such. At this point the preciptating material is dissolved in the aluminum like sugar dissolves in water. After solutiuon annealing, the aluminum is baked at about 250 deg F for a set time (time and temp depend on the alloy). The most common precipitating addition to aluminum is silicon or copper. The highest strength for the aluminum is just before the silicon or copper actually starts to separate out of the aluminum in particles.

Precipitation hardened aluminum that is heated over time becomes weaker and more brittle with time and temperature as the particles of silicon or copper get larger and less silicon or copper remains dissolved in the aluminum. This condition is called over-aging and the microstructure of the material would show a lot of precipitated inclusions in the aluminum.

Powder coating is usually baked around 300 to 350 deg F which is way below the solution annealing temperature, but well above the temperature needed to get the silicon or copper to come out of solution.

The only way to fix over-aged material is to re-solution anneal the material by heating the material to somewhere around 1000 deg F, quench and then re-age the material at some time and temperature around 250 deg. F.

[philbur]

How does a fixed mass of gas in a tank with a fixed volume increase in density by increasing the temperature.

Phil

It has infinite heat capacity which means an increase in temperature increases density instead of pressure.

[Rich Carlstedt]

Thank you PR and Jpfalt !
Good concise explanations
My experience is with high pressure liquids (15 K PSI) and Hoop failure. and decidedly different results.
Most likely because of the non-compressable nature of liquids (?)
Rich

(non-compressable as compared to gases.)