Propylene vs propane

[CRAFTBENDER]

I did a search on the forum but couldn't get a good answer. Also called my gas guy and he couldn't tell me much except that he can't fill my propane tank with propylene. I can readily forge weld high carbon in my gas forge but low carbon mild steel is very borderline. Has anyone used propylene in their forge and can you tell the difference. If there is a difference, I think having a switch over valve from propane to propylene, since propylene is more expensive, for welding and then switch back to propane for forging. OK, I'm ready for answers. Thanks.

[Thomas Dean]

Not sure about a forge and the use of propylene to forge weld, sounds expensive to me... I do know you cannot weld (torch) with propylene and oxy.

[Frosty]

It will take more than a simple switch of a valve to make it work. While I don't know what the ratio is I'm sure it's different from propane. There could well be a necessary change of jet size involved.

What I'd do is reduce the volume of my forge if it's getting close but not quite. A split brick layer laid on the floor should do the trick nicely. Perhaps some kiln shelf would last longer and heat faster. It sounds like you only need to reduce the volume 50-75 cu/in to me and that's easy.

Frosty

[Charlotte]

Ok here's the story. I worked for many years in the industrial gas biz as a Laboratory supervisor. What I'm about to tell you is the truth and nothing but the truth as I remember it.

Propylene has a higher working vapor presssure than propane, about 19 Psi in fact. Your gas guy may be prevented, for a number of commerical agreements and his specific license for gas filling from the DOT, from filling your container with propylene.

DOT Regulations controlling Pressurized gas filling and transportation are contained in 49 CFR. I am not current on the CFR because I'm ten years out of the business. However, I do know that the shift to current propane consumer valve, from CGA 510 was connected with a number of unfortunate incidents in which people boosted cylinders from industrial plants that contained compounds that were dangerously posionous when burned. As a result that and other regulations were also tightened.


Now to your Idea. Propane Propylene, Methyacetylene, and Propadiene in various mixture ratios are marketed as MAPP Gas, Blazer, Chemtane etc.

The is a lot of smoke and mirrors involed with these brand names, lawsuits, patents and copy rights. It all boils down to: they are essentially the same thing. They will weld mild steel horizontal forehand. They produce higher preheats than straight propane and are thus easier to start without producing the same over heating experienced with acetylene.

Without going in the chemistry involved, yes it is possible to raise a forge's temperature by changing to a different fuel gas. But keep in mind that it will probably involve changing to a different orifice size and tinkering with your pressures and volumes to get it running satisfactorily.

I've tried the experiment you are contemplating: At one time I had two gas forges and a number of crawfish burners going. I fueled these with propane range hydrocarbons that were scheduled for disposal. My conclusions were this;

1)Yes it does make a hotter fire.
2)If you are having trouble getting to welding heat for mild steel you need to look at your forge design and burner design.

Possible problem. What is your altitude? That does influence the temperature you can reach in an atmospheric gas forge.

A blower and a regenerative system will solve that problem.

Re-generative system is simply putting a stack on your forge that routes the dragons's breath over a pipe that feeds air into your burner.

I advise against going to a different fuel gas than Propane or Methane. It costs more for not much benefit.

[Thomas Dean]

Charlotte, you stated in your above post that you can weld with propylene and others. (did I read that correctly?) My understanding is that you cannot weld with propylene using a torch. (due to the high pressures needed as you mentioned) When using this gas, for cutting purposes, it is recommended to use a tip 2 sizes up from what you would use with acetylene. Or is the welding you are refering to only in a gas forge?

[MattBower]

Did some reading about this a while back when I was exploring the possibility of switching to oxy-propane over oxy-acetylene (b/c acetylene skeers me a little more than propane, and b/c propane is cheaper and more readily available). The conclusion I eventually came up with is that it's possible to weld with a lot of oxy-gas torches, but (except with acetylene) the welds will tend to be low quality and hydrogen embrittled.

But they're fine for cutting, and in rosebuds for brazing and heating.

Don't ask me for citations. I don't have 'em anymore. But it's a big Internet.

[Charlotte]

Charlotte, you stated in your above post that you can weld with propylene and others. (did I read that correctly?) My understanding is that you cannot weld with propylene using a torch. (due to the high pressures needed as you mentioned) When using this gas, for cutting purposes, it is recommended to use a tip 2 sizes up from what you would use with acetylene. Or is the welding you are refering to only in a gas forge?

Actually I was talking about the "proprietary" Gas mixes. The trick they use is to put a lot of methyacetylene and Propadiene in the mix. This raises the temperature just enough, when combined larger tips to permit welding forehand horizontal. There are three factors involed here. Temperature, quantity of heat, hydrogen embrittlement.

I have extensive experience with MAPP in particuliar. Thin mild steel well fluxed for non-critical applications were ok.

I loved using it for silver solder, brazing, all kinds of copper work.

I keep a small cylinder of acetylene for the rare occasions when I really need to fusion weld something. The last item I used it for was decorative door hardware that broke for a friend of mine. It was one of those fancy "faux" colonial things. I would not have tried it with Mapp or with tig as the first is too much heat( quanity) and the other is too high temp and too much heat.

Normaly I cut with oxy/propane because I tend to do a cleaner job with it. The little extra O2 in preheat doesn't matter compared to what is use for cutting.

[CRAFTBENDER]

Thank you for your answer, also thanks to all. On the forge and burner design. I used the Michael Porter book to build my burner and forge. I think the burner is fine but I did a search for burner size to volumn and in one, Dodge said in a post that a properly tuned 3/4 inch burner would heat up to 350 cubic inches to forge welding heat. My forge is seven inches in diameter and twelve and a quarter inches deep. If I figured right that comes to 470 cubic inches. Another fellow said 250 cubic inches max for a 3/4 burner. The doors have about one by four inch rectangular openings. So if this is the case, I guess I need to add another burner or decrease my volumn. I never figured the volumn before this, but you would think the propane cylinder design in Porter's book would figure this in.

 

[Frosty]

Ah HAH! Try laying something on the floor of your forge like I suggested above to reduce the volume of your forge. One of Mikey's burners would be just shy of welding in that much volume. Like I guesstimated, all you need is 50-75 cu/in less volume.

A second burner on the other hand will make welding a shoo in, no question about it, watch your iron or it'll melt on you proposition.

Thank you for the excellent info on the hopped up fuel gasses Charlotte, it was an excellent read.

Frosty

[CRAFTBENDER]

I did figure in your post before this one and decreasing the volume by putting in a brick plus Charlotte's questioning the design of the burner or forge. This is what impelled me to find the burner volume ratio. The only problem with the brick is that I couldn't get anything else in there. I've decided to add another inch of kaowool to the inside to decrease the forge diameter to 5 inches which would give me about 240 cubic inches. More heat, less fuel. Thanks again.

 

[Frosty]

Sorry, I just got a little excited to discover I was right and had to yodel a bit.

The burner : volume ratio is the first thing I go into when asked about building a forge.

The extra Kaowool will be better than adding a layer to the floor. It will make for a long narrow forge though so the heat won't be as even through out.

Frosty

[CRAFTBENDER]

Frosty, you are forcing me to waver. If I do two burners, what should be the spacing in a depth of 12.25 inches?

 

[Frosty]

I'd put them about 5.5" apart measuring from the center of the forge. If you put a 1/4 turn ball valve on each you'll be able to run with one for general forging.

Frosty

[Superscout]

Thank you for all of your insights, since I work for a major gas distributor and can purchase propylene for your cost of Propane, I think I will go the propylene route. That will solve problems of supply and size of containers, plus I can have a truck pickup and drop off for me. Now has anyone used oxygen injection on their naturally aerated burners, or would that be too hot?

[Frosty]

Welcome aboard, glad to have you. If you put your general location in the header you might be surprised how many members live within visiting distance.

Oxygen is completely unnecessary if you build and tune the burners correctly. 

Frosty The Lucky.

[timgunn1962]

What are you doing in a forge that needs hotter than Propane can get?

I know that a Naturally Aspirated Propane forge can get hot enough to melt Wrought/Pure Iron, because I've done it, albeit unintentionally. 

Oxygen injection can increase the flame temperature by reducing the proportion of Nitrogen that gets dragged along for the ride. Burning a cubic foot of acetylene in air releases exactly the same amount of heat as burning a cubic foot of acetylene in Oxygen. It's just that burning it with Oxygen, those BTUs are just heating the products of combustion, whereas burning in air, they are heating the products of combustion plus the Nitrogen (and trivial amounts of one or two other gases) that makes up the rest of the air.  

 

Sorry, fat-fingered.

Oxy-Acetylene is used when really high temperatures are needed, such as when welding. 

We don't normally need the sort of temperatures in forges that are only available using expensive Oxygen, so it makes more sense to expend a bit of effort, rather than money, tuning the burner to get the temperature we want. This is generally a case of getting the appropriate air:fuel ratio.