Oxy/propane vs. Oxy acetylene for cutting,etc.

robmc · Oct 5, 2011

I've always used acetylene in larger torches. I need a small torch for my home shop but something bigger than a Bernzomatic. What's been anyone's experience with propane or similar fuels for cutting and heating.... performance wise? What about oxy/gasoline torches?

snowman · Oct 5, 2011

I run oxy-propane for brazing/cutting. I find it just as useful. It is my understanding that it heats up slower, but it still works.

Plus it uses the same gas as my grill. I've got a lot of those tanks.

JST · Oct 5, 2011

ALL the UP railroad stuff I saw was running oxy-propane when they replaced tracks up the hill from work....... big tanks labeled propane, no way to be mistaken about that.

Mike C. · Oct 5, 2011

O/P doesn't get as hot as O/A in terms of flame temp, but a big huge O/P rosebud can put out GOBS of heat. I use one regularly at the shop for heat shrink fits, dropping large iron stators out of aluminum and cast iron housings and general heating jobs. I als use ti occasionally for cutting. Great advantage to cutting with O/P is that it does not get as hot as O/A, so you are forced to use proper cutting technique... you preheat and then let the oxygen stream cut the work instead of melting it and blowing out the molten material. Cuts VERY cleanly with very little slag.

On the downside, you can't weld with it. Just doesn't get hot enough. For the homeshop, I'd get an O/A and be done with it. Don't get an air conditioner repair set with the tiny tanks. They are OK for quick soldering of tubing, but useless for metal working. Get 80cuft tanks.

Conrad Hoffman · Oct 5, 2011

If you're not going to gas weld, propane is the way to go. IMO, it's safer for a home setup. If you need to weld, you need acetylene. Watch out for the withdrawal rate on small acetylene tanks; you can't use a rosebud with 'em.

mark thomas · Oct 5, 2011

What Conrad said.

I am not sure about btu/dollar, but my propane is sure a lot less expensive to fill than my acetylene.

I have a very small acetylene tank for my rare gas welding, and propane for everything else.

Mike C. · Oct 5, 2011

Last 80cuft acetylene refill I got was about $20. Gas grill bottle refill is $18 at Wally World.

mark thomas · Oct 6, 2011

Mike C. said:
Last 80cuft acetylene refill I got was about $20. Gas grill bottle refill is $18 at Wally World.

Interesting. My last MC (10 cu ft) acetylene refill was $22. My last grill bottle was $10.

Maybe on the acetylene they hit you more in smaller tanks. A decade ago I ago I had an 80 ft tank and it was about $20 to fill. I sort of assumed the current $20 for 1/8 the volume was inflation, but maybe I'm getting creamed because I'm buying "hobby" quantities.

Curious about the btu/dollar though.

DaveE907 · Oct 6, 2011

BTU per dollar is no contest, propane is always less expensive. A 20 lb gas grill propane tank is about 432,000 BTU gross heat of combustion. An 80 cubic foot acetylene tanks is about 118,000 BTU gross heat of combustion.

Use any price per quantity you like to do the math with these numbers:

Propane: 21591 BTU/lbm or 2490 BTU/ft**3

Acetylene: 1470 BTU/ft**3

Performance wise?

For only cutting and heating propane will do the job and it's safer than acetylene too.

As a teenager in the 50's I burned cars apart in a wrecking yard with oxy/propane, it works very well. There were no concerns about the fuel detonating if mishandled either.

Oxy/gasoline is primarily used for cutting heavy stuff. It's not a likely upgrade from a propane torch in a home shop.

adama · Oct 6, 2011

Oxy propane works great for me. Especially as i already had a AC-dc tig welder. Due to the bottle rental schemes here there's at least a £50 a year saving in bottle rental using propane. That's before you compare the costs of the gas. If you have a good cutting nozzle and run the preheat hard they make a great heating torch for small bending and straightening jobs. Equally it brazes - silver solders nicely too.

abarnsley · Oct 6, 2011

Up at the mine (Gold) I use both.

Cost seems cheaper for propane ... But it takes A LOT longer to start a cut.. BTU's are fine, but Highest possible heat counts too...

Propane is cheaper, and performs like a Chinese knockoff of Actylene.. For cutting thin things (auto bodies) it works..

The special torch tips help a lot.

For serious steel cutting, say over ~ 6 inches we use Oxy Actylene. It gets the job done. Why waste time...

For us the highest costs are the O2 bottles.. The Actylene is only a small part of the cost.. When cutting, we can usually run 2 ea O2 cylinders for 1 Actylene cylinder. On propane it seems like more 1 to 1.. This makes sense, due to gas flow/BTU/highest heat.. Gas prices vary locally of course..

We do have a couple Actylene generators laying around.. Calcium Carbide is fairly cheap.. As is water.. Australia might have a problem though..

It is pretty easy to set Actylene regulator to under 15psi.. Kind of like not running 220 to a 110 device...

Damn Canadians can't even mark their cylinders right though

You would think it would be easy to standardize colors on a single continent..

We get cylinders from where next supply run is headed..

DaveE907 · Oct 6, 2011

"It is pretty easy to set Actylene regulator to under 15psi..."

Absolutely right. Ever been around an acetylene regulator that failed to hold that set pressure? I have... Stay vigilant and safe.

Mike C. · Oct 6, 2011

mark, I just happened to notice the price of a propane refill at Wal Mart this weekend... $17.44. $52 without exchange.

surplusjohn · Oct 6, 2011

all the serious scrappers I have seen doing cutting us propane and LOX for cutting, so obviously cheaper, I was told it was hotter but it sounds like it can deliver faster vs hotter.

WizardOfBoz · Oct 6, 2011

I knew that OxyAcetylene was hotter than OxyPropane, but how much. I looked up the idealized value for temperature (the "adiabatic flame temperature") and found widely varying values (!). Don't believe everything you read. In any case, for one source the difference was about 300°C:

Acetylene - Oxygen: 3100, also 3480°C
Propane - Oxygen: 2820, also 2526
Acetylene - Air: 2400, also 2500
Propane - Air: 1980, consistent

MAPP - Oxygen: 2980, also 2927
MAPP- Air: no value, 2010

I could recalculate these, but the view is not worth the climb. Suffice to say that there is at least 300°C (nearly 500°F) difference between the two fuels. In any case, it would seem that (as Hank Hill would say) if you can do the job with propane, you are dollars ahead.

9100 · Oct 6, 2011

Abarnsley, have you considered getting an oxygen generator? They do not actually generate O2, but separate it from air. Purity is not as good as bottled oxygen, around 95%, but the operating cost is far lower, mainly the electricity to run a compressor. You also have to get the air really dry or the zeolite in the generator will fill up with moisture and you need to trap compressor oil, but the great thing about them is you never run out. When we were silver brazing locomotive contacts all the time, we used propane and generated oxygen. The generator used regular shop air, so there was no extra installation there. I was on the verge of getting a natural gas pressure booster several times, but the work volume fluctuated so much that it was never a clear choice. Natural gas / generated oxygen would not only have lowered the cost drastically vs oxy / acetylene that we started with, but it would eliminate the logistics. Whenever a batch of contacts came in, we had to do the estimate of the gas consumption and the amount remaining in the tanks. It really irks me to trade in a tank with gas still in it, but sometimes the trade off was interrupting the job in the middle to go fetch gas, worse than losing a little on the gas.

Bill

Bill D · Oct 6, 2011

How about natural gas which is mostly methane. my father had a ng/compressed air torch for soldering. just a little more then a Bunsen burner. no reason it could not be hooked to O2.
Bill D.

9100 · Oct 6, 2011

Bosley, I think a lot of the variation in temperatures can be attributed to the size of flame and exact mixture used. The flame is going to entrain cold air, the smaller the flame, the higher percentage. Something not mentioned here is that the flame propagation rate of oxygen / acetylene is so much higher than oxygen / propane that you can push a lot more BTUs through a given orifice without having the torch blow itself out. A big tip with flame holders can generate a lot of BTUs with propane, but they are spread out. We developed our own torches that ignited the fuel stream inside the head before the gas velocities got high at the exit opening. We could run the pressures up to where it was a choked nozzle at Mach 1 with a shock line across it and several shock lines visible in the flame. It put a lot of heat in a small area, but hearing protection was mandatory. I considered marketing the torches, but was afraid some fool would ruin his hearing and sue me.

Air with any fuel is a bummer because you are blowing 4 times as much cold nitrogen on the part as there is oxygen burning and trying to heat it.

Bill

tomwalz · Oct 6, 2011

Gas comparison chart
temperatures, heat values, etc.

Brazing with Gases

DDoug · Oct 6, 2011

I like propane/ox for removing (by cutting) as I can get the torch in the corner
of somewhere and not have it pop and flashback.

I also like it because I can burn off 1 piece from another and not nick the
other piece. Other's can do it with acetylene, but I'm just not that good,
acetylene always seems to "jump over" to the other part too easily and ruin
what I'm tying to save.

Oxy/propane vs. Oxy acetylene for cutting,etc.

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