Oxy/Acetylene - Any cheaper alternative to BOC

On or around Mon, 1 Sep 2008 13:54:15 +0100, "BRAD" enlightened us thusly:

dunno. Best bet would be find yer nearest large steel molishing type place and see if you can do a deal.

Air Products have fewer hoops to jump through, but still want bottle rental by DD, I think.

I suppose technically you could buy a set of bottles, and then exchange them.

Not wishing to teach my grandmother to suck eggs here, but I can vouch for what others have said about the dangers of pressurising acetylyne even a relatively little bit. A regular Guy Fawkes night trick was to fill a condom with oxy-acetylne mix which then makes a great bang when the bonfire's lit. Then on about the 3rd occasion my mate did this, the gas detonated whilst he was filling it - what initially appeared to a Laurel and Hardy moment was actually rather more serious and he'd perforated both ear drums. Although his hearing did return somewhat, some damage was permanent and, for instance, he could no longer go scuba diving. This is only at balloon pressure remember. There was a view that the condom lubricant was a contributory factor, so presumably risk can be reduced by keeping a carbide generator very clean and oil free. I've also heard of the gas evolving from "spent" carbide exploding when being carried in a sealed container - an ammo can used for carrying stuff in caves. It went off when banged on a rock, slightly injuring the hand of the bloke carrying it. He said he'd have been hurt rather worse if the rock hadn't been shielding him from it when it went off. (carbide lights used to be used for caving)

Hywel

Oxy-acetylene mix is even more dangerous than acetylene - by far!

The ignition energy required is less than 1/10, maybe 1/100th of the ignition energy of aceteylene itself - which is still low.

Acetylene/oxygen mixes can detonate at 1/10th atmospheric pressure, or less.

Pure acetylene by itself is not just dangerous by detonation, which requires maybe 18 psia - it also deflagrates (burns slowly - but slowly can be anything from very slow to bl**dy fast indeed!) at lower pressures than pure acetylene, including less than atmospheric pressure.

Then on about the 3rd occasion my mate did this,

:(

I have holes in both my eardrums - I can (or could - they seem to be blocked now) blow bubbles from them in the bath. Maybe they've regrown, or filed with wax, but loud bangs do that.

This is only at balloon pressure remember. There was a

No.

Cleanliness and oil-freeness are requirements - but as I said above, the ignition energy of acetylene/oxygen mixes is very low indeed.

The acetylene/oxygen ignition energy is far less than the ignition energy of the condom lubricant in oxygen, probably ooms less - but then perhaps even a bursting balloon might give enough energy to ignite an oxygen/acetylene mix.

Not kidding.

I've also heard of the gas evolving from "spent"

Not surprising. Spent carbide is dangerous, and will give off acetylene for a good while.

Still are, occasionally.

I did sanity-check this, but I'm so drunk right now that I'm not sure of my own sanity -

- and I'm not infallible anyway, as my lack of fingers will attest.

-- Peter Fairbrother

Im-Pure acetylene by itself is not just dangerous by detonation, which

im-pure acetylene

^^ detonates

, including less than atmospheric pressure.

bleeaarggh

-- Peter Fairbrother

If there is one thing I have learned since the advent of the Internet, it is never to reply in public when drunk. I always regret it.

Cliff Coggin.

Y'rright of course. Let me rephrase my reply, hoping this is clearer:

hyweldavies wrote: > Not wishing to teach my grandmother to suck eggs here, but I can vouch > for what others have said about the dangers of pressurising acetylene > even a relatively little bit. A regular Guy Fawkes night trick was to > fill a condom with oxy-acetylene mix which then makes a great bang when > the bonfire's lit.

Oxy-acetylene mix is even more dangerous than acetylene - by far!

The ignition energy required is less than 1/10, maybe 1/100th of the ignition energy of acetylene itself - which is still low.

Acetylene/oxygen mixes can detonate at 1/10th atmospheric pressure, or less. Acetylene/air mixes can explode below atmospheric pressure too, which is why it's important to flush acetylene hoses immediately before use.

Acetylene without oxygen can not only detonate, which only takes place at 15 psia or more, but it can also deflagrate at any pressure.

(A deflagration is when the reaction front moves slower [1] than the speed of sound in the material - if it moves above the speed of sound it's a detonation, that's the difference between a detonation and a deflagration. When a reaction front moves faster than the speed of sound some of the energy goes into making shock waves, which can be very damaging.

[1] for acetylene slower can be anything from very slow to very fast indeed!)

Most flashbacks in acetylene hoses are deflagrations, not detonations. Sometimes acetylene burns inside the torch without oxygen, and that's a deflagration too - but the occasional "pop" may be a detonation of oxygen/acetylene mix.

Another example of a deflagration is in the regulator of an acetylene cylinder - this *always* happens to some extent when acetylene is used. Acetylene regulator passages are made small to limit the volume and thus lower the rate of reaction so that only a small proportion of the acetylene decomposes, and to ensure the deflagration does not become a detonation.

So don't use anything except a proper regulator designed for acetylene with acetylene!

Then on about the 3rd occasion my mate did this, > the gas detonated whilst he was filling it - what initially appeared > to a Laurel and Hardy moment was actually rather more serious and he'd > perforated both ear drums. Although his hearing did return somewhat, > some damage was permanent and, for instance, he could no longer go > scuba diving.

:(

I have holes in both my eardrums - I can (or could - they seem to be blocked now) blow bubbles from them in the bath. Maybe they've regrown, or filled with wax, but loud bangs do that.

This is only at balloon pressure remember. There was a > view that the condom lubricant was a contributory factor, so > presumably risk can be reduced by keeping a carbide generator very > clean and oil free.

Not my view. As I said above, the ignition energy of acetylene/oxygen mixes is very low indeed, far less than the ignition energy of the condom lubricant in oxygen, probably OOMs [2] less - but then perhaps even a bursting balloon might give enough energy to ignite an oxygen/acetylene mix.

Not kidding.

[2] orders of magnitude

I've also heard of the gas evolving from "spent" > carbide exploding when being carried in a sealed container - an ammo > can used for carrying stuff in caves. It went off when banged on a > rock, slightly injuring the hand of the bloke carrying it. He said > he'd have been hurt rather worse if the rock hadn't been shielding him > from it when it went off.

Not surprising. Spent carbide is dangerous, and will give off acetylene for a good while. A polythene bag should be okay, but not a metal container in which the gas pressure can rise.

Still are, occasionally.

-- Peter Fairbrother

Also used at party time, balloon with OA inside, nitrogen tri-iodide outside.

The other use of welding kit on Guy Fawkes night is handing out old, damp arc welding rods to the youngsters, telling them that they are sparklers and watching their attempts to obtain ignition from the bonfire. Once the kidz have gained a nice cherry-red colour we give them real sparklers, otherwise it would be unkind.

Where do you buy driplamp carbide these days? Halfords no longer stock it. Wouldn't mind a bit to play with, for old times sake.

Regards,

David P.

I have available an unopened sealed canister of carbide - stated average contents - 6.25Kg.

Should be enough for a spectacular bonfire night if anyone is interested.

Jim

In article , Peter Fairbrother writes

IIRC from my chemistry days, acetylene under pressure does indeed have a material tendency to explode spontaneously (quite possibly encouraged by the metal of the cylinder walls). The acetylene cylinders used actually contain the acetylene dissolved under pressure in liquid acetone, and (again, IIRC) some solid material to stop it all slopping around.

Also worth bearing in mind that the acetylene/oxygen reaction is *much* more exothermic and violent than that of propane or butane. I once saw a demonstration of a stoichiometric mix of the two in a milk bottle being ignited (very carefully with a long rod and heavy screening); all that was left afterwards was powdered glass ( and a loud ringing in the ears).

Don't try this at home folks....

David

In the UK it's usually porous diatomaceous earth and cement, sometimes with carbon added, which completely fills the cylinder. The acetone comes about half-way up.

The porous stuff is there primarily to prevent detonations; but it also filters the acetone from the fizz caused by decrease in pressure when the valve is opened (that's why an acetylene cylinder should be kept and used in an upright position).

The porous stuff will also slow a deflagration (a non-detonating flame front) - but it won't stop one. If a cylinder starts vibrating or rocking and gets hot, get out of there fast!

That sounds like a detonation - which can be much more violent than a fast deflagration (flame). Acetylene/oxygen mixes tend to detonate much more easily than eg propane/oxygen mixes.

For an acetylene/oxygen mix initially at atmospheric pressure the maximum shock pressure can reach 6,000 psi for a detonation (as opposed to about 90 psia for a deflagration).

I won't repeat it all here, but I just posted a whole lot of information about acetylene (probably much more than you want to know) on the sci.engr.joining.welding newsgroup, under the thread titles "Splitter on Acetylene tank" and "Another acetylene question."

-- Peter Fairbrother

Here in South Africa we have Afrox which is a subsidiary of BOC - it is also regarded as very expensive.

I use oxy/propane and I purchased my most recent oxy refill from a gas outlet (which gets the refilled cylinders from Afrox) and paid less than I would have from Afrox - and I got to chose my own cylinder!

This is a recent press release from Afrox: "The factory currently exports more than 50% of its total production. The BOC group, Afrox's parent company, was recently acquired by the Linde group. This is likely to open up many new export markets for the factory's products."

Tim