gas torch for propane question

I've bought an oxy propane cutting torch set: torch (PNMS nozzle),
regulators, hoses and flashback arrestors. It's fine for brazing but the
cutting torch is a bit big and unwieldy. I asked a welding supplies bloke if
I could use his type 5 oxy acetylene welding torch with propane - I was told
no, the gas is corrosive in copper nozzles and the nozzle may explode.
I've seen shanks offered with oxy/propane mixers. Are these only to be used
with the cutting attachment, or is there a welding nozzle that I could use
with propane?

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A bit of education before you buy is a lot more efficient than buy first, learn later...
Oxy-propane cutting rigs exist because acetylene is expensive and more than a wee bit hairy (deflagration) in ways that propane hasn't thought about. For anything thinnish they have largely been displaced by plasma cutters which are even cheaper to run.
But you can't weld (at least not well) with oxy-propane because oxy-propane simply isn't as hot as oxy-acetylene. Of course, gas welding is a bit of an anachronism these days because any of several arc processes is usually cheaper and faster - and I say that as a guy who likes to gas weld (and owns a big frigging stick welder anyway - it's faster and cheaper for most things.) Much of what I would have done with OA rather than stick in the past I'd do with TIG or MIG now.
The main compatibility issue with propane .vs. acetylene equipment is the hoses - some types will take both, some will work with acetylene but fail with propane, IIRC. Been 20 years or so since I cared all that much about it, having picked a path and stuck to it. I don't recall any particular issue with copper, and have used lots of propane stoves and other appliances that used copper fuel lines for 40 years or more without any corrosion problems...
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Greetings John, The welding supplier is correct. Acetylene gas flowing through copper can form copper acetylide. This compound is very explosive and very easy to set off. Shock, heat, or just the fact that the stuff exists is enough to set it off. It is more sensitive than silver acetylide which I am familiar with. I made the stuff 40 years ago and boy was it easy to set off. So don't go using copper nozzles or tubing with acetylene. Eric
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Thanks for your answer and the information - I might not have been clear enough in my original post.
I appreciate that you can't weld with oxy propane - I bought it for brazing. I was taught brazing at school and have had success with it over the years. I have been brazing at a friend's farm - using his oxy propane cutting torch. I bought a set of my own for convienience - it wasn't expensive. I just wondered if there was a smaller torch that would run on oxy propane and be a bit less cumbersome that a cutting torch.
I appreciate that there are modern welders that could be used to weld things that I braze: motorcycle exhausts, thin bits of tube and the like - but I don't have the skill to be able to use them. I have no opportunity of learning the skill and only need to braze about 10 times a year. I do have a cheap stick welder and have used it to make several trailers but I usually blow holes in thin stuff with my stick welder - another reason why I like brazing.
Another advantage of me owning an oxypropane kit is for heating things up for bending.
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I am aware of the issue with copper acetylide and that brass fittings in the acetylene line must have a copper content below which problems don't occur to prevent issue with it but all my OA cutting tips appear in colour to be a high copper content or near pure and no problems so I wonder if the exposure time to pure acetylene needs to be factored in. For the cutting tips I have the main time is spent with an acetylene oxygen mix and only initial light up sees pure acetylene for a short time so maybe the copper acetylide reaction doesn't get very far.
Reply to
David Billington
A friend uses an OA torch, IIRC a high pressure mixer type, with oxy propane and the copper tips supplied were modified for oxy propane use by the supplier. The tips look to be the standard copper tips for OA use but a countersink has been used on the end of the tip. I suspect the small countersink in the end of the tip is a flame retention feature but not sure. All in all the tips are copper and work fine.
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David Billington
It's acetylene which can form explosive substances with copper - that's a definite. Not propane+copper ???
They obviously alloy the nozzle with something which prevents acetylene exploding in copper nozzles - or the nozzle gets hot enough any reactions products decompose as fast as they form - or something like that.
Rich S
Reply to
Richard Smith
nope, no explosives there.
There is (at least sometimes) oxygen inside the plain copper nozzle as well as the acetylene, which deters the formation of acetylide; the nozzle also gets hot, which prevents the formation (the acetylene polymerises instead above about 180C in the presence of copper or copper oxide as catalyst); the heat also causes any copper acetylide which might have been formed to decompose or react with oxygen; and the oxygen also forms a layer of copper oxide on the inside of the nozzle preventing formation and buildup of copper acetylide.
Also, when the torch is switched off, air enters the nozzle, and any acetylide formed reacts greedily with water in the air to form acetylene and copper oxide.
The black goo inside a nozzle is mostly copper oxide and polyacetylene which has reacted with anything it can find to form a very thick and sticky goo. This goo then prevents the acetylene from reaching the copper.
Buildup of copper acetylide is dangerous in several ways, but buildup in nozzles isn't one of them - first, if the copper has been exposed to acetylene for a very long time, it can build up into a thick enough layer of explosive to cause significant damage.
That takes a long time on a flat surface, and copper acetylide is very sensitive, eg if it's in a hose it will detonate if the hose is flexed, usually in such tiny quantities no-one even notices - so large-scale buildup is only really dangerous with static tubing which has been in place for a long time.
The second way in which buildup can be dangerous is if the acetylene is at near-explosive conditions, when a smaller amount of copper acetylide detonating can detonate the acetylene. This would be very rare with proper modern equipment (if it had copper in it) and welding conditions, specifically the use of void fillers and acetone when the acetylene is at any significant pressure.
Third, if copper is used in a regulator,especially the small parts,the acetylene can eat away at it and maybe cause leaks.
Fourth, the use of copper in flash arrestors can be very dangerous - some of them have a sintered blob of metal with a very large surface area on which acetylide can build up.
I expect there are a more which I haven't heard of or thought of. Moral, don't use copper with acetylene, except for nozzles!
-- Peter Fairbrother
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Peter Fairbrother

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