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Up Topic Welding Industry / Technical Discussions / Oxygen Cutting with Methane instead of acetelyne
- - By batanony (*) Date 11-16-2008 12:15
Hello all,

I have a question here which puzzles me. Can we replace the acetelyne with methane in the oxygen cutting process?. The reason behind this question is because here in my country, Egypt, methane is available more than aceteleyne and less expensive. besides, it is an exothermic reaction where the fuel gas is only needed at the begnining.
Parent - - By 803056 (*****) Date 11-16-2008 19:34
The temperature (of the flame) produced will be lower, so the time to reach the ignition temperature of the steel will be somewhat longer. Once the ignition temperature is reached, cutting should proceed without any problem.

You will need to switch to a cutting tip that consists of a two piece unit that is made specifically for the type of fuel gas you are using. Your supplier or the manufacturer of the cutting torch should be able to offer you the correct information on which tips to purchase for your torch.

Best regards - Al
Parent - - By welderbrent (*****) Date 11-17-2008 00:56
Al,

Just for my own info, and I guess anyone else who might be interested, does methane burn anything like Propane, Propylene, MAPP, or Natural Gas?  I have used all of these through the years and the major difference to Acet seems to be the lower temps and the tip (all use the two part tips).

Mona,
Is the methane a city supplied gas or a welding supplier?

Have a Great Day,  Brent
Parent - - By Superflux (****) Date 11-17-2008 01:14 Edited 11-17-2008 01:55
Methane (C4H4) is what we in the USA call "natural gas". The later has to have Mercaptain (that smell) added and be free of H2S and other impurities when it comes out of the ground before used by your local utilities company.
Yes, a Natural Gas 2 piece tip is what you need.
Parent - By welderbrent (*****) Date 11-17-2008 01:19
Thanks John,  Just personally curious about what others are actually using.

Have a Great Day,  Brent
Parent - - By DaveBoyer (*****) Date 11-17-2008 03:11
Methane is CH4, not C4H4.
Parent - By Superflux (****) Date 11-17-2008 05:52
Dave,
thanks for that correction. Too many 420's in my chemistry.
Parent - - By aevald (*****) Date 11-17-2008 03:57
Hello batanony, as you can see from the replies, everyone has told you that you can certainly use the methane gas in combination with oxygen to perform your cutting requirements. One item that wasn't discussed was the reasoning behind having to use various types of tips in order to accomplish this task. If you go to a welding supply store and look closely at the various cutting tips that are designed for the different cutting gas combinations you will see that they have various recess depths for the different gases. This has to do with how combustion occurs at the end of the tip. Fuel gas, oxygen, and "air" combine to provide the proper conditions to support the cutting process. By varying and controlling the depth of the combustion end of the cutting tip it is able to properly mix and control this combustion process and provide the optimum flame. I am going to try to attach a link to a Smith comparison chart that may better explain the differences. Best regards, aevald
Attachment: P-8142.pdf (146k)
Parent - - By 803056 (*****) Date 11-17-2008 04:53
You said it very well.

Best regards - Al
Parent - - By batanony (*) Date 11-17-2008 06:51
WOW!!! First, thank you all so much for the extensive and clear information.
Well, here in Egypt, we have alot of oil fields in different locations, where most of the outcome products is condensated into natural gas or methane CH4 while only little left into oil.
Thanks again and i will buy the suitable tip and start working with it. Promise to send you some pics to see the results.

Mona
Parent - - By aevald (*****) Date 11-17-2008 19:45
Hello batanony, I did finally manage to find the chart I was looking for, at first I thought that it was included in the link that I had posted. Instead, here is a photo of it, we have it hanging in our classroom here at school. Best regards, Allan
Parent - By welderbrent (*****) Date 11-17-2008 23:36
Thanks Allan

That makes a great addition to my training materials and easy proof for some of the questions on my pre-employment written exam.

Have a Great Day,  Brent
Parent - - By batanony (*) Date 11-18-2008 06:08
Thanks alot Allan. The figure indicates that the natural gas has the least flame temperature, which means the preheat is longer as i expected. I just hope that the quality of the cut surface is acceptable or not less than the acetelyne or so.
Thanks again so much :)
Mona
Parent - - By TimGary (****) Date 11-18-2008 13:31
Hello batanony,

As far as cut quality is concerned, you'll find at first, that cut quality is much less with methane vs. acetylene.
This does not mean that the methane is not capable of making a quality cut.
It simply means that the two gasses burn differently and there is a definite learning curve that your torch operators will have to get used to.
The quickest way I've found to expedite this learning process is to make sure the operators grind their own cuts clean.
There is no better quality cutting teacher than a heavy Black & Decker Wildcat 7 1/2" grinder.

Tim
Parent - - By batanony (*) Date 11-19-2008 06:08
Hi Tim,

What do we mean by grind their own cuts clean? Do you mean grinding after cutting? Is that ok ? Because i thought you would inspect the cut surface after cutting for comaprison and analysis. Another thing please, is there a technique that should be followed during cutting with other fuel gases than acetylene?
Thanks alot

Mona
Parent - By aevald (*****) Date 11-19-2008 07:40
Hello Mona, I'm going to jump in here just a bit. What I believe Tim is referring to, has to do with the operator doing the cutting having to clean slag and possibly grind edges square or other post cutting steps prior to being able to use the cut part. If they have to do much of this sort of thing they will be more likely to pay attention to the quality of the cuts and minimize the time spent doing additional preparatory work. There are certainly a bunch of visual aids that will help a person who is using a cutting process do a better and more efficient job, I believe Smith, Victor, and a host of other cutting equipment manufacturers have such information. In many cases they include pictures that can be used for comparisons to cuts and by using these comparisons you can make changes in the cutting process to improve the quality. In most cases, I don't believe the issues concerning cut quality will be related so much to fuel gas as they will be to proper tip size, travel speed, coupling distance, flame settings and pressure settings. Hope you are enjoying this learning track and best regards to you, Allan
Parent - - By TimGary (****) Date 11-19-2008 13:39
Hello again batanony,

aevald summed it up well, as usual.
My comment was based more toward manual operation of hand torches, which typically require manual cleaning, or grinding, afterward to remove residual slag and to smooth cut edges.
Machine operations will not be as troublesome, but as aevald stated, all of the parameters will change.
Each different fuel gas will have it's own parameters in order to obtain the best quality cut for the thickness of steel being cut.
You can expect slower travel speeds and an increase in fuel gas CFH usage.
This should be offset, as far as overall cost is concerned, by the decrease in fuel gas cost.

Please let us know how it works out for you.

Tim Gary
Parent - - By welderbrent (*****) Date 11-19-2008 15:22 Edited 11-19-2008 16:08
Mona,

A couple more points to Allan's well put explanation if I may.

1) In D1.1 clause (formerly 'section') 5.15.4.3 (p. 195 of 2006 ed.) there is a stated roughness requirement.  That directs you to some ANSI numbers and then a reference put out by AWS that describes the roughness and you get a moulded sample to compare the product to for quality of finish.  AWS C4.1 is what you need to order.  Maybe a couple of them, one for the work station and one for QC person.

2) Having used most types of fuel gases on both hand and machine cutting operations through the years there is another point that is not made often.  There needs be almost NO slag nor clean up time with any of them especially with machines.  I don't even 'hammer' with a slag hammer.  Run it along the edge and any small debris falls off, ready for the next step.  Now having said that it takes a lot of practice and experience to produce to that level.  If the edge is not to be welded or hidden in some way some may want to hit the edge quick with a sander or grinder for a little better appearance but it is generally unneeded.  If you hear lots of hammering or grinding then something was not setup correctly.  Tip size, preheat or cutting pressures, speed, tip properly cleaned, distance from tip end to material, and possibly a couple I have missed.  I worked one machine that we had to rework the bearings and track system because it was so loose you could not get good cuts from all the jerking and bouncing that the unit did as it moved.

3) Since you asked about different techniques between the two gases, what thickness of material are we talking about and what grade (A-36 carbon steel or other) of material.  What is the intended use for most of the product after cut process (welded joints, individual complete part as cut, etc.)  There are things that can be done to improve quality of cut with a quick learning curve but there are various applications.

I think that about covers it from my point.  Good luck.

Have a Great Day,  Brent
Parent - - By batanony (*) Date 11-20-2008 11:10
Dear Allan, Tim, Welderbent and everybody here,

Thank you so much for the sincere concern and detailed description as usual 
Well, as I told you before, Egypt is a big producer of natural gas. I think the industry here should just make use of this advantage not available for everyone. We noticed, me and the professor I am working with, that still most of the workshops or related industries rely on the acetylene as the fuel gas in the oxyfuel cutting processes. So, what I am trying to do some is to conduct limited series of experiments to cut different thicknesses of low carbon steel (A36) with the natural gas and try to publish this out for alls' benefit here. The thicknesses are 3mm, 6mm, 10mm and 12mm. do you think these thicknesses are enough?

I think in doing so, we are saving a lot of money here.

I almost have all the equipment and the operator ready. The welder himself is worried and afraid to try the natural gas. He wants me to use these mixtures used at our houses in ovens (mixture of propane and butane). He said he tried this before and it is safe. He thinks that cutting with natural gas is not safe!! I think it can't be more dangerous than acetylene. The only concern would be when the gas is in direct contact with air. Right?

So if I have set the working pressures, the proportions of oxygen to natural gas, the preheat time, and made sure of hoses being in good condition, then that is it.
Anyway, I am preparing the procedures from the materials you sent me and others as well.
If you do not mind, I am sending you this procedure to take a final look at it before going ahead in the experiments.

P.S
I am enjoying this Allan more than you could imagine :)

Thanks everyone
Yours truly,
Mona
Parent - - By Superflux (****) Date 11-20-2008 12:17
Safety is only as good as the person following the "rules". I can't think of any reason why methane would be any greater hazard than acetylene. Methane might be stored in a much higher pressured container, but acetylene in its free state is unstable after 15 psi. Oxy-acetelyne has a much hotter flame than any of the other gases. From my thinking, acetelyne requires more precautions (note, I did not say more dangerous!). As for the mixed gas issue, that I would think is purely economical..costs /cu. ft. and container handling vs. perhaps supplied via pipeline into the shop. Anything can be unsafe, and a hazardous material if handled improperly air, water, a sack of flour etc. I've worked with explosives in the past (wiring detonation cord to RDX shaped charges...) in the oilfield perforating formations. Kind of scary in concept, just follow the rules...DON'T deviate! Once again...Safety is only as good as the person following the "rules".

"The only concern would be when the gas is in direct contact with air. Right?"  This holds true to any flammable gas. What about unlit and exposed to pure oxygen?

After about 16mm you might want to consider preheating a little (dry run as we used to call it, follow the cut line using the pre-heat only), but, after 20mm, it is advantageous to preheat using acetylene.

Wish you success in your experiment.
John
Parent - - By welderbrent (*****) Date 11-20-2008 16:57
John hit the items I was considering.  The thicknesses are you propose are easily cut with natural gas as the fuel.  We used it for years in a pipe forming shop I worked for.  They had it piped in as it appears you are doing and had it piped to each major work station where we attached our equipment and went to work.  We used it to 3/4" (18mm) with no problems.  As John stated, at about 1/2" it pays to run over your cut area to pre-heat.  Improves the quality of the cut enough to make it worth the time.  I often would warm my heavier section from the bottom side with a hand held torch as well.  It is the side opposite where the torch will be running that doesn't get as much heat even when you pre-heat. 

Safety is a consideration in all stages of welding and with all fuel gases.  No more so really than with propane, propylene, acetylene, or MAPP. 

If you have a good chart so you can get the right tip from your supplier for the thickness being cut, monitor travel speed, proper gas pressure maintained, everything should go very well.  Good Luck.

Have a Great Day, Brent
Parent - - By Superflux (****) Date 11-20-2008 21:15
Yes,
"Weed burners" are an efficient tool to pre-heat pieces a square meter or over in size.
Parent - - By welderbrent (*****) Date 11-20-2008 22:15
Now that you mention it, we used to use those to pre-heat the sides of tanks in cold weather ahead of the submerged arc girth welders for CBI.  I generally use either a regular torch head or a rosebud in similar fashion to what you had mentioned but from the bottom of the plate instead of the top.

Have a Great Day,  Brent
Parent - - By Superflux (****) Date 11-20-2008 22:26
welderbrent,
Yes excellent advice, pre-heat from the bottom and "dry run" from the top. On dirty or excessively scaly steel, two dry runs, 1st pre-heat only to loosen the scale, then another run over with the cutting jet on to blow away the scale, can make for quality cuts.
Parent - - By welderbrent (*****) Date 11-20-2008 22:40
Absolutely.  And if burning freehand, do rough layout, run torch over to 'pop' mill scale, rust, etc off, then do accurate lay out for cutting.  Takes time, but you'll get a better finished product.  Could have a helper wire wheel whole thing first, but then a lot more gets cleaned than what may need to be.  Or, just buy new, clean steel in the first place.  Should be so lucky.

Have a Great Day,  Brent
Parent - By Superflux (****) Date 11-21-2008 01:36 Edited 11-21-2008 02:12
Cup stone on grinder
Parent - By Superflux (****) Date 11-21-2008 01:38
Wire wheels don't usually stand a chance against millscale. That's some bad to the bone stuff.  "Or, just buy new, clean steel in the first place.  Should be so lucky." What planet and quadrant of the galaxy do you weld in??? Got any more openings??? Have hood ..will hyperspace there tommorow or yetesrday if (super)flux capicitor is at full charge!!!
Parent - - By DaveBoyer (*****) Date 11-21-2008 07:30
    With regard to safety, the hoses should be grade "T" I believe this is neoprene. The grade "R" and "RM" hoses commonly used with acetylene are not compatible with other fuel gasses, and will detriate prematurely.
Parent - - By batanony (*) Date 11-21-2008 14:22
Well, i did not know this hoses issue. So, do u really think the normal ones used with the acetylene are not used with the natural gas? Ok then i'll have to look for the "T" type you mentioned.
Thank you guys so much and you are really making things easier for me to prepare. only some points left to sum the whole thing up for the experiment. I am still working on the precedure i am going to follow. Looking forward to sending it next Sunday

Thanks again and regards to all of you.

Mona
Parent - By TimGary (****) Date 11-21-2008 18:09
Dave is exactly right.
I had forgotten all about that.
Good point Dave!

Tim
Parent - By welderbrent (*****) Date 11-21-2008 19:22
There is 'safety' in a multitude of counsellors.  That had appearently not crossed several of our minds till now.  Most all the gases outside of Acetylene require a different hose for a totally proper set up.  Thank you Dave for reminding us.

Have a Great Day, Brent
Up Topic Welding Industry / Technical Discussions / Oxygen Cutting with Methane instead of acetelyne

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