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Up Topic Welding Industry / General Welding Discussion / Liquid Oxygen
- - By rcwelding (***) Date 12-23-2010 21:35
I was talking to my welding supplier today when a guy that works for a salvage yard came in and asked for liquid oxygen...

  I guess this salvage yard is cutting all day long with a A/O torch and they were going through regular oxygen tanks like crazy so this supplier switched them to liquid oxygen.... They claim they get twice the usage out of a liquid oxygen tank then they do a regular tank...

  I told my supplier I wanted to switch over and he told me if I wasn't cutting steady it would be a wast because liquid oxygen is VERY unstable and it will vent all the time because it builds so much pressure in the tank...

   It sounded a little crazy... Have any of you guys used liquid oxygen in a torch..??

Parent - - By Joseph P. Kane (****) Date 12-23-2010 21:47 Edited 12-23-2010 21:57
The dealer told it straight.  The LOX tank is always bleeding off product to relieve pressure and maintain temperature.

Using LOX on a rig should only be considered if you are doing salvage or demolition or have a very large cutting job.  You should also consider using LOX if you are using a large diameter burning bar,

The LOX tank is actually a precision instrument compared to a high pressure AA cylinder.  It is quite easily damaged.  Using a rig to transport the LOX Tank around subjects the tank to possible handling damage.  Usually you are responsible for any damage to these very expensive tanks.

In a shop, where you have an automated Oxy -fuel multi-station cutting operation it may also be economic.  If you use the equivalent of a LOX tank in a  week, the LOX tank will certainly be more economical.

Joe Kane
Parent - - By rcwelding (***) Date 12-24-2010 01:26
Thanks for the info..

   I guess that salvage yard was going through three tanks a week before they switched over...

Parent - By DaveBoyer (*****) Date 12-24-2010 03:55
The liquid tank is an insulated tank with liquid inside a tank that holds oxygen in the gas form. The liquid boils off even tho under really high pressure and is held in the outer tank for use. If You don't use it before the pressure in the outer tank gets to a set limit, it will vent off to reduce pressure.

Liquid argon tanks operate the same way, and have the same disadvantage if not used continuously.

The auto frame plant had a large stationary liquid oxy tank, I was told that there were 3 chambers, one with the liquid and the other 2 for gas, high pressure surrounded by lower pressure. I didn't hear it from anybody of authority, just second hand information. A liquid truck came to refill it. These make little effort to prevent loss, the gas is boiling off and venting all the time.
Parent - By welderbrent (*****) Date 12-23-2010 22:15
Joe and your supplier are correct, at least as far as my research a few years ago went.  I checked into it while in a shop that had a four head pattern burning machine and half a dozen fit/weld work stations.  It is very good in the right kind of usage but few shops can fully utilize the process.  And I personally would not recommend it for anything but shop operations.

Have a Great Day,  Brent
Parent - - By fschweighardt (***) Date 12-24-2010 03:51
Well, I have a bunch of scrapyards that use several liquid oxygens a week, you can hook a guy up with a big bottle of propane/propylene and they can cut all day.  A liquid holds something like 10 standard cylinders.  You can hook them up to an external vaporizer and get lots of instantaneous flow capacity for a lance.  They are pretty handy for the correct application.  Just your everyday ordinary user will probably not benefit much.
Parent - - By rcwelding (***) Date 12-24-2010 04:23
Will propane work better on a rosebud..??  I have been having problem with mine popping something terrible lately... I didn't know that they were only good for just so much flow before the acetone starts cumming up...I just learned about that... I think that is part of my problem now... Im going to shut my PSI way down and try to run a smaller flame to see if that helps..
Parent - By weldwade (***) Date 12-24-2010 04:37
Check your hose RC. If it is rolled up unwind it completely with NO kinks.
Parent - - By DaveBoyer (*****) Date 12-24-2010 04:48 Edited 12-24-2010 04:52
If Your rosebud is too large for the cylinder output, the pressure will drop off as You are working, and give You problems. Look up the CFM of the rosebud then figure the available gas delivery of Your tank using the 1/7 rule which is now the 1/10 or 1/15 rule. You probably have too large a rosebud for the cylinder.

See this thread:

Propane or propalene will have the same problems if You draw hard enough on a small tank, but not nearly as bad as with acetylene.

Check the specifications on Your rosebud, many are fuel specific, You may need a different one for propane.
Parent - - By Superflux (****) Date 12-24-2010 08:56 Edited 12-24-2010 10:33
Turning the flame down will not help. This will only increase the popping. If you throttle down a tip, you run the risk of turning it into a "machine gun"!
These tips (come in different sizes and therefore) are designed to operate at specific flow rates and pressures. This relationship creates an optimum velocity and quantity of gasses exiting the tip to properly support the combustion. A delicate balanced flame obtained through the relationship of pressure and volume. Think of this as an External Combustion Machine as opposed to the Internal Combustion Engine of you truck and welding machine....
Another variable not yet addressed is hose length and diameter when using rosebuds. In order to supply the required CFM (at fps of velocity)...ya gotta have a bigger hose (yes! size matters!) along with multiple cylinders. Per manufacturers instructions, I doubt you would be in compliance with any rosebud using 3/16" hoses. The consumption rate for heating tips needs a larger diameter hose than most field operators are going to have on their trucks. Yes it is a money thing. Acetylene is unique to fuel gasses due to the instability of pressures above the 15 psi. There is no safe substitution of jacking up the pressure to provide the volume required when dealing with acetylene. If a rosebud is popping, it means only one are starving the insufficient quantity of gasses. They also require a certain volume of ambient oxygen to maintain the flame. This is why even cutting tips will "pop out" when the tip is too close to the work or up inside a tight confined space.

Getting back to the original topic...Some jobs require will just require more of a specific "consumable" than others. This is what dictates the type of container needed. Would I want to carry around a bulk tank of O2 or Argon on a rig truck all the time??? Depends on if my daily tasks were cutting or purging.
Parent - - By welderbrent (*****) Date 12-24-2010 13:01
To add just a little more to Superflux's excellent explanation:

It is possible you are running too low of pressure on your Acetylene.  Many people forget to up the pressure from below 10 lbs for cutting to between 10-15 lbs for heating.  But if you are up on your pressure and it is popping then many of the above suggestions can apply.

Hose size is important.  Even 1/4 and 5/16 may not be large enough.  3/8 is often needed for the main run if there is much distance then down size on a short whip at the end.

Propylene works well in many, though not all, instances.  Can be used at higher pressure than Acet and produce more volume.  But there are other drawbacks.  Takes some getting used to. 

And when a tank is laid down for transport, storage, etc you don't have to wait any time at all for it to 'settle' before striking up the torch.

Have a Great Day,  Brent
Parent - - By rcwelding (***) Date 12-24-2010 13:23
Thanks for the info guys..!!!!

  I was running 10lbs Acetylene and I want to say 30lbs of oxygen.. It is a big rosebud...

I was only running 50ft of 1/4 in hose...

I didn't have any problems with it when I bought it but the last couple times I used it I had the machine gun effect going on...

My Acetylene bottle is getting low too... My cutting torch works great but but that rosebud is running a little cranky... LOL

Parent - By welderbrent (*****) Date 12-24-2010 14:07

Try running your Acet on the top side of 10 but keep it under 15.  And try your Oxy at about 50.  On larger Rosebuds and really cranking it on I have run them up to 60 lbs Oxy (I believe, it has been awhile).  With the propylene you can put some pressure to that as well.  I ran off the 25 gal (100 lb) tanks and had them opended up pretty good.  Seems like around 25 lbs.

Have a Great Day,  Brent
Parent - By JLWelding (***) Date 12-25-2010 16:06
Also check the oring where the rosebud screws on.
Parent - - By NMWELDING (**) Date 12-24-2010 22:35
I know it sounds odd but I use the same length and size hose,same regulators,try the same settings,tanks are always upright as they should be,yet in the last maybe 5 or 6 years I get the popping effect when using a rosebud. I`ve used a rosebud in the oilfields for nearly 27 years now and never use to have this problem when I was a rookie. I actually have more use for a rosebud in my line of work but don`t use it like I did in the past because of this.I have also noticed [likely not related]and other welders have said the same when I asked them, that the acetylene doesn`t seem to ignite like it used to 15 or 20 years ago,it`s more difficult to ignite.Maybe it is all in my head,but I don`t think so. Any comments appreciated.
Parent - By Superflux (****) Date 12-25-2010 01:55
This straying away from the LOX.
I'm gonna open up a torch topic in Tricks of the trade.
- - By Fritz T Katt (**) Date 12-24-2010 17:14
I was taught that acetylene above 15psi goes BOOM. Unless it is stabilized by the acetone.

Which would not be enjoyable...

I was also led to believe that liquid oxygen will remain a liquid under enough pressure (such as CO2), where it can then be drawn slightly so when the pressure is then low enough it will boil to raise the pressure back up.
Parent - - By Northweldor (***) Date 12-24-2010 18:52
You were "led to believe" wrongly if they did not tell you about the boiling point of liquid oxygen (about -297 degrees F.) Because of the difficulty of maintaining this low temperature, even under very high pressures, the need for venting arises.
Parent - - By Fritz T Katt (**) Date 12-25-2010 01:19
Ah, ok.

I have also always wondered how the oxygen doesn't just dissolve the whole tank and valve itself. I have seen pictures of people putting oxygen in precharged airguns, and those results where not pretty for the gun nor shooter. It was explained that the oxygen dissolved the onboard tank itself, along with the valve.

My guess is the inside of the tank has some coating to prevent contact between the gas and the wall.
Parent - - By Northweldor (***) Date 12-25-2010 13:10 Edited 12-25-2010 13:12
I think you may have been misled here, as well, (although I am not familiar with these guns) since the oxygen in industrial (welding) tanks would not "dissolve" either the tank or the valve of those tanks. What does happen, under unusual circumstances, is that high-pressure oxygen comes in contact with other flammable substances, usually hydrocarbons, with explosive results. Once the oxidation process starts, sufficient heat is generated to oxidize ("burn", not "dissolve") almost any material (the basis for the oxy-acetylene cutting process).
I suspect the lubrication in an air-gun's mechanical action may be responsible for initiating a similar rapid oxidation (explosion) when exposed to high-pressure oxygen, but this is only a guess.
Parent - - By rcwelding (***) Date 12-25-2010 15:38
When I was a 10yr old kid helping my grandpa building horse pens out of old boiler tube and sucker rod he used to always tell me to NEVER put any kind of grease in, on or around his torch and Oxy bottle because grease and Oxy could spontaneously combust if the two met...

  He was a great BS'er... I always thought he was full of beans...

Parent - - By Fritz T Katt (**) Date 12-25-2010 17:25 Edited 12-25-2010 17:29
North, I most certainly agree with that theory, although anyone using such a weapon should know (not saying idiots don't exist LOL) never to use petroleum based lubricants. It's a major thing for airguns because just the use of them along with high pressure air will provide enough to combust. EDIT: I have also been taught the oxy-fuel cutting process uses the first stage to heat the metal to near melting. Then the second stage (cut lever) increases the oxygen output to not only blow away the semi-molten metal, but rust it away. This leads to why stainless steels cannot be cut with this process, because they resist oxidation.

RC, has grandpa been proven wrong? I for one agree with his idea. For this reason we are told to never used oxygen in place of air for pneumatic tools, or even to blow dust off a table. Maybe after break I will take a bit of oil and blow some oxygen on it just to see what happens.

My question of why does an oxygen bottle not dissolve (rust) itself to bits still remains. Ferrous metals (of course) are used to make the bottle, and as we all know oxygen bonds with iron to form rust. Does the simple pressure prevent this reaction?
Parent - - By DaveBoyer (*****) Date 12-27-2010 03:16
I think the oxygen tank survives because at normal temperatures, the oxygen and steel do not combine readily or rapidly.
Remember that steel does not rust in dry air, but there is enough oxygen in air that steel wool wil burn, if ignited.

The steel does not rust away in the presence of the oxygen in the torch, it burns like paper in a fire.
Oxidation is a broad term, it covers a lot of oxygen reactions at varrying speeds.
Parent - By Northweldor (***) Date 12-27-2010 12:33 Edited 12-28-2010 12:14
Fritz, in addition to Dave's comments above, the steel of the oxygen cylinder is an alloy surely designed to resist oxidation, similar to the way "stainless" resists oxidation, by forming a layer on initial exposure that prevents further oxidation, without more expensive chromium and nickel addition. ( I know only that the steel used is a type of armor plate, but some of the metallurgists on here might tell us more?) Think of "mill scale" and "pickling" as examples of other cheaper ways to slow or prevent oxidation.

Also, your description of the cutting process is not accurate. The preheat flames heat the metal only to the ignition point, and the heat of the burning process heats the metal to the molten state.
Up Topic Welding Industry / General Welding Discussion / Liquid Oxygen

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