Propane - Cutting & Welding - Tombstone ???

[rjmack]

Propane is now the preferred fuel for oxyfuel cutting for economic and safety reasons

never seen it on a construction site, doubt that i ever will.

it's just not as good.

you say it is the oxygen that does the cutting, but the accelerated oxidization process (cutting) won't occur without sufficient preheat. propane doesn't bring the steel/rust/grime etc up to temp nearly as fast or keep it there nearly as long. if you are familiar with aluminum welding, you know that the aluminum oxides melt at a higher temp than the aluminum itself... well there are contaminants that you run into in the field that act the same way. just because you have the steel up to temp doesn't mean that what is on top of it is up to temp. and if what is on top of the steel is not going to oxidize or become molten enough to blow out of the way, then your cut cannot proceed.

when you see companies like bechtel/kbr etc start going to propane in the field, then you may have an argument, in the meantime, there is no reason it can't become the preferred choice of people who don't know the difference.

like i said, it is used in shops, on clean fresh steel, not in the field. (actually, it is mapp gas and butane that are primarily used in shops, but very close to propane)

maybe the tip technology may improve to a level comparable to acetylene someday, but i don't think that day is here yet.

 

[IslandTractor]

Look up the acetylene v propane cutting discussions on welding forums. I think you will find that propane cutting is very popular especially in the field where only cutting is done. Scrapyards for example. It is also used industrially especially with very thick cuts. Lots of misinformation about propane but I think you will see it is gaining popularity due to cost, convenience and safety versus acetylene. There is a slightly different technique to cut with propane and this is where a lot of confusion occurs. Propane flame is hottest further from the tip than acetylene so using acetylene technique with propane is inefficient. Rosebud sizes for acetylene go up to 250,000btu/hr. Propane rosebuds go up to a million btu/hr. That says something.

 

[rjmack]

Rosebud sizes for acetylene go up to 250,000btu/hr. Propane rosebuds go up to a million btu/hr. That says something.

i suspect that difference has to do with available flow rates, all the same, rosebuds aren't used for cutting.

like i said, i have never seen it on a job site, and i have been on many. too many perhaps. :laughing:

 

[Gary Fowler]

i don't know where to find the link, but iirc acetylene has a much higher btu output than propane. pretty sure that temp and btu are not exactly relative numbers.

the analogy being that btu of cutting flame is approximately equivalent to torque in an engine being used for towing... the more torque the better. propane is a low torque fuel... good enough for clean surfaces (gang torches in shops) but not so good at digging through dirt, rust, oil, paint etc.

According to my references, propane has a higher BTU output than Acetylene, but it burns a bit cooler. I have never used propane for cutting, but used MAPP (propylene) on one KBR job back in the 70s. It heated a bit slower and left lots more slag on the cut. The welders complained enough that I never saw it used again. I have to say, that lugging around a bottle of MAPP was a heck of a lot easier than a big old acetylene bottle but that was the only advantage other than cost maybe. I think the reason we used the MAPP was because of a shortage in acetylene due to all the construction, the gas suppliers couldnt get enough so they started selling the MAPP, at least that was their story.

 

[yomax4]

Every scrap cutter I know uses propane and it's just because of cost. I use both and like them equally. Acetylene cost is why I use both. I solder and braze with Acetylene and cut and heat with Propane.

 

[IslandTractor]

Every scrap cutter I know uses propane and it's just because of cost. I use both and like them equally. Acetylene cost is why I use both. I solder and braze with Acetylene and cut and heat with Propane.

Exactly my point about the economics. There is also something to be said about the convenience of trading out a 20lb propane tank at a local gas station or Home Depot on a weekend too compared to being dependent on the LWS store.

Soldering with propane is common but there is no reason propane cannot be used for brazing either.

I enjoy welding with acetylene but for cutting it seems a bit of a waste (other than the convenience if you already have the set up for welding).

 

[lostcause]

when rjmack mentions "in the field" and bechtel and kellog brown & root he's not talking about billybob and bubba cutting up old chevys to sell for pennies a pound, he's talking about multi-hundred million dollar construction sites.

the local junkyard uses propane/oxygen, the fab shop that runs 15,000+ tons of steel a year used mapp/oxygen when i was last there. all the small garages & individuals i know use acetylene - probably because they have the equipment already, and historically had to use it for welding as well as cutting.

 

[rjmack]

when rjmack mentions "in the field" and bechtel and kellog brown & root he's not talking about billybob and bubba cutting up old chevys to sell for pennies a pound, he's talking about multi-hundred million dollar construction sites.

that's my point, they use it because it is better.

i build quite a few little projects related to my property, so i am using fuel gas probably as much as most diy'ers. i bought oxygen and acetylene bottles to avoid demurrage costs. my acetylene bottle costs about $100.00 dollars to fill, and i need to fill it now after about 3 years. the costs/savings, as a backyard guy, are insignificant compared to the pita associated with using propane as a cutting fuel.

The welders complained enough that I never saw it used again.

when welders complain about something, there is usually a reason... spoken or otherwise. :laughing:

shops use it because their automated cutting tables operate under ideal conditions. far as junkyards/scrappers... i'm guessing those using mapp/propane haven't taken into account the increased cost of using a lot more oxygen (they don't exactly give that stuff away either) under the exact conditions where acetylene leaves propane/mapp etc in the dust. it takes a lot more volume of oxygen to run propane than it does to run acetylene. propane has a fairly narrow range of combustion where as acetylene has a wide range. so when you are running much larger preheat tips, they are burning much more oxygen as well... not to mention all the oxygen lost when you repeatedly press the cutting lever only to have the cut fail.

i only know of one scrap dealer, most of his stuff comes already small enough to load on a truck, but if he does have to cut, he uses acetylene.

 

[IslandTractor]

i bought a propane tip and regulator to cut up an old dump truck box that came with a 3 ton truck that i only wanted the engine out of. the truck was an old municipal plow/salt truck and was rusty.

i never had such a tough time trying to cut anything up in my life... swore i would never use propane again... and i won't.

others have had different experiences i guess, but my nightmare was real. propane doesn't have nearly the btu of acetylene, as such the preheat time is much longer. if you are running a gang torch or automated cutting table that's not really an issue because you are always cutting clean steel, but i found that it kept losing it's preheat. i would lose the cut and have to stop and wait for it to generate enough heat to start the cut again.

i have never seen propane used in the field and i'm pretty sure that's the reason. sounds like you are going for it, so i guess you'll find out for yourself.

I'm wondering if your attitude towards propane is related to using the wrong technique. As has come out in this thread, if you use acetylene technique when cutting with propane you will surely be disappointed. Cutting up an old dump truck though is something that most scrappers today would use propane to accomplish. Holding the flame further from the steel than with acytelene is critical due to the nature of heat release with propane vs acetylene.

I also own oxyacetylene equipment and certainly agree with rjmack that I would not use propane unless it was convenient or I was intending to cut an awful lot of stuff up. The OP's question though was essentially whether propane was a cheaper way to preheat and cut and I think that has been pretty well established. Oxygen is cheap and the extra oxygen used is easily paid for by the cost differential between propane and acetylene. In settings where a few minutes of a welders time is worth more than the cost differential in fuel, acetylene might have a small advantage. The welding instructor I worked with has thirty plus years in iron work and he uses both. Acetylene if it is convenient but propane if he sets up specifically to heat or cut.

 

[crackerjack222]

There have been several comments about the relative strengths of propane vs acetylene. According to my book:

Gas BTU/Cuft / Flame temp with air / Flame temp with O2

Acetylene / 1475 / 4800 / 5600-5900
Propane / 2520 / 3800 / 5300-5610
Mapp / 2400 / 2680 / 5300
Methane / 1000 / 3800 / 5025
(Nat gas)

Just trying to add to the base of knowledge here, which is already quite good...