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?
John
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...
--
Cats, coffee, chocolate...vices to live by
Please don't feed the trolls. Killfile and ignore them so they will go away.
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.
John
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
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
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
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.
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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