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Kevin (The Professor)

Question about safely cutting former propane bottle for forge

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Hello Everyone,

I have a propane bottle that is approaching its, "expiration date," after which they will not fill it at my local hardware store. I have been advised by some cheapos to just take it to one of the bottle switching stations and get a new one from them. \

 

But, I don't want to do that. Stealing or tricking someone out of something that is only worth $30 just doesn't appeal to me. Not that I am wealthy, but I do have my pride.

 

So, I am thinking of making a propane forge out of the old propane bottle (Matthew Parkinson has one at his shop that gets screamin' hot off of one venturri burner, and I bet I could plug one of the burners from my Chili forge into a smaller forge and get good performance). I want to try.

 

Which brings me to...

 

What is the safest way (other than have someone else do it for me) to vent this thing and make sure it is really empty before I go to cutting with a cutoff wheel on an angle grinder? I have a cutting torch, but I have never actually used it. I just use the oxy rig for high heat torch work, not cutting.

 

Please don't just tell me it is dangerous (I know that part). But, if you have a practical solution to this problem, I would really love to hear it.

 

thanks,

kc

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Almost blew myself up years ago, cutting into a hundred pounder. Oddly enough, wasn't with a cutting torch. I had flushed the tank with water and Simple Green, but still had flammable gas somehow.

 

I ended up filling the tank with water, just under the top weld line, and cutting with a torch.

 

The advice I got after all that was to buy a new tank, of whatever size, and cut into it. They come new with an inert gas in them (which is why the filling station should ask you if it's new, so they can purge the inert gas).

 

Dan

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Hmmm... Seems like you could also purge with inert gas/water. They sell this stuff called "bloxygen" which is just a can of nitrogen. It's used for keeping things like wine, paint, and wood finished fresh and unoxidized, so you may find it at a woodworking place, a hardware store, or a wine store.

 

Second, do not use a torch on a tank no matter what. There's always a little unburned gas in the cutting flame which can accumulate inside the tank. Get enough in there and BOOM!. A cutting wheel on an angle grinder is not much safer if there's any flammable gas in there. Maybe if the tank is full of water, but that would be messy. I'd vote for drilling a hole, then using a reciprocating saw. Still wet. Far less chance for sparks that way, and sparks are the problem.

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In the past what I've done is this; Make sure it is as empty as you can get it just by letting out the gas. Put it about 75 yards away and shoot the tank with a rifle. Make sure to shoot the part you're going to be cutting off anyway. There typically isn't enough gas to really do anything, and at 75 yards you ought to be safe.

 

 

This could be silly advice though, so use your best judgement. However, I've never had an issue with doing it this way.

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I opened my valve to make sure it was empty, and let it sit in the summer sun for a week or so with the valve open. Then I removed the valve (unscrewed it) and left it for a couple more weeks in the sun. Then I put it in a brush pile, lit the fire and stood back. Never had a pop/bang from it. Sure it doesn't look as nice now since the paint burned off and it got all sooty, but after that you know that any more flame can't do anything to it. I did this living in western Washington, so "summer sun" is a relative term. ;)

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I like Jerrod's method! Still don't use a torch unless the tank is full of water, a cutoff wheel ought to be fine, and I forgot to mention the valve thing. Do that!

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I like the shooting it part best. Good thinking Nate. (Even if Jerrod's advice seems to be the best.) With the valve unscrewed and the tank filled to the top w/ water I can't see any gas remaining.

 

Side note: I have a buddy that has a 600 acre ranch in Eastern Oregon w/ a long firing range. He shot a full #20 tank with a 50 cal to see what happened (at like 1/2 a mile out) and it didn't explode, just went whizzing around like a little drunk rocket. When he used a tracer round, however, boom! #donttrythisathomekids

 

Grins,

 

Dave

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Perhaps turn the valve open to make sure there is not gas under pressure in the tank, then remove the valve entirely. Then you can blow air from a shop compressor in through the bottle mouth for a while to remove any remaining gas, doing the same while cutting through the tank to remove any gas buildup from the cutting torch. Any thoughts?

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I've got one full of water sitting outside my shop right now.

 

I couldn't get the valve to unscrew, but I took the stem out and had enough hole for a trickle. Just sat on the porch, talking and letting the hose trickle. Filled up soon enough.

 

No guess work here... she's full to the top.

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Jerrod is pretty much spot on. I've made probably 20 tongue drums outta these. Pull the valve first thing. Fill with dishsoapy bleachy water and let it sit over night. Propane accumulates in an oily mess, and permeates the metal, the older the tank the worse the mess. The soap and bleach help break it down. Empty it and let it air for a day or 2. (it will smell like @#$%). Then you should be good to cut it anyway you chose I always pass a torch over the bung hole just to be sure but never had a flash. I usually use a sawzall, but have cut them dry in this condition with a torch or plasma cutter several times, no issues.

 

All that being said a new unfilled tank is $30, and between the hassle, and the smell that is the route I would go.

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i remove valve and let sit for a few days or so lay it on its side or upside down for heavy gasses a little water wont hurt to get some of the accumulate smell additive from the bottom of the tank real old tanks can have a bit :P shop smelled for weeks after i turned a 100lb upside down to weld to it with a puddle of the stuff in the bottum all ran out when i applied heat

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Propane is heavier than air, so leaving the tank upside down lets the propane drain out. The one time I did this we pulled the valve, and let it sit upside down for a couple of days, filled it with water, drained it, and cut it with an angle grinder and a cutting disk. We had no problems.

 

Geoff

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I have made a number of forges from 20# propane bottles. I always open the valve to let out any gas. With the newer bottles just opening the valve won't let the gas out. You have to depress a stopper in the valve. When in use the part that screws into the valve depresses this stopper. I have never been able to remove a valve without heating it, which I would not do before drilling the hole. They seat the valves with a lock tite type product and I have never been able to get the bottle clamped so that I can unscrew the valve with out heating it. I then drill a 1/2" hole so that I can insert a saber saw blade and start cutting. One time when I drilled the hole I smelled propane. I held a lighter over the hole and it whispered "poof". No flame just a quiet little "poof". I normally then do all of the cutting with the saber saw, reciprocal saw, or angle grinder with a cut off wheel. The propane smell is the oil they put in the tank to cause the distinctive odor. Sometimes in a 20# bottle there is enough to wipe out with a rag. See my tutorial on my web-site at the forge supplies page. www.WayneCoeArtistBlacksmith.com.

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I've done what geoff did more than once. Totally accident free.

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I knew this was a question people would answer, since this group is pretty quick to try and prevent death or injury among it's own.

 

thanks guys.

 

I am going to do a hybrid (no shooting, since I live in Ct). Darn shame, wish I hadn't sold the farm in Texas, but alas, no choice.

 

Anyway, I will use the soapy water trick, and cut full and wet.

 

kc

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big rule NEVER use a torch to cut any tank (even with water in it) good ideas are to as said remove the valve and invert the tank. then drill into the opposing side (after flushing a few times and giving some time) with holes at both ends it gives anything that could build up a place to go .. I generally grab old uncertified tanks from my gas supplier and he has already removed the valves and flushed the tanks.. most of the time I use a plasma cutter to do the cutting. I have in the past (before I had a plasma cutter) used drills and cold chisels, 4 1/2" grinders with cutoff wheels, a band saw and even a hack saw.

As long as all of the Liquid propane and just about all of the gas is gone, it isn't all that dangerous, the biggest worry is building up pressure with out a place to go... that can be ... bad.

MP

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This is me, and I live out west, so I'd take it out in the middle of nowhere, back off a good distance, and shoot a hole in it with my rifle. (Apparently Nate and I think alike)

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buck make sure the valves off and theirs no fuel in the tank or when it gets hit it will possibly split rather than have a nice hole punched in it

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The thing with shooting a fuel tank of any sort is a "Standard" round. It will NOT set the Tank Off ! However, a "Tracer" Round will as it has an ignition source "Fire" behind the round look up "Myth Busters " they did a test on this many times . Remember Propane is a petroleum base product and can gel. leaving a residue in even an "Empty Tank"

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Don't be cutting tanks full of water with a cut -off disc on a grinder, disc failure is a very high probability.

 

The crap they put in the propane to make it stink is the real problem, not the propane.

A water flush will remove all gas, or turning it upside down without a valve, as has been mentioned.

 

The additive will leave a waxy build up over time in the tank, and condensation is a real problem at fill stations and commercial re fillers as well, so some moisture gets into the tanks and also adds to the tank gunk.

The gunk is flammable, but not particularly volatile, and the tanks should not be explosive after emptied of gas and allowed to fill with plain atmosphere. Tanks used in more cold climates have more gunk.

 

If the valves are out, and the tank has been left upside down or filled with water and emptied again, there should be no explosion hazard, ,although the gunk may be ignited and will burn for a short time.

 

I have cut open many many propane bottles of all sizes and types with cut off discs, saws, and plasma cutters, and have had a few flames occasionally, but never anything even resembling a small pop and certainly no explosions.

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I've had great luck at removing the smell from old tanks by putting a copious amount of bleach in with the initial fill of water. I fill to overflowing and then let it sit with the bleach water for a couple of hours. No gas smell with the water that I pour out. The spot where I emptied water out of my first tank (before I learned the bleach trick) still smells slightly of that additive. The most recent tank didn't have the slightest smell, even after the first fill. Yay!

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Hello Marti and welcome to the forum! :D

 

I am always so very pleased to see female bladesmiths (or aspiring bladesmiths). The craft is very lopsided in terms of gender balance.

 

Hope to see your work shared here someday soon!

 

Dave

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