# propane tank forge



## Ski (Apr 11, 2017)

Hello, I am going to build a propane forge and I am looking for the proper procedures to prep a propane tank for cutting the ends off. I currently have the valve removed and the tank strapped upside down. It has been outside now for a couple weeks and I was going to do a water purge prior to cutting  but thought I would ask the question here first. Nothing showed up in a topic search.  It is a 100 lb tank. I will be using a cutoff disk in a 4 1/2 grinder to do the cutting. Thanks ahead. Ski


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## Bob Korves (Apr 11, 2017)

Fill it with water before grinding or welding on it, or get some really good earplugs!  You are probably OK after letting it sit upside down for a couple weeks, but who knows?  You are the test pilot...


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## chips&more (Apr 11, 2017)

I once tried to repair a Model T gas tank. The tank had been laying outside for decades with the gas cap off. When I looked inside the tank, it was bone dry and not a hint of any gas smell. So, I went and started up my torch and when the flame touched the outside of the tank where I was going to fix it. The air inside the tank ignited and shot a huge flame out of the filler neck!!!! I had to go change my underwear on that one. And the tank puffed up and could not save it. I was just a teen when that happened. But to this day, I respect gas containers empty or not!


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## dlane (Apr 11, 2017)

Purge with argon real good , I knew a guy that cut them all the time by running his car exhaust thru the tank for a half hour. With that said I made my forge from a portable air tank , no fumes


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## Ski (Apr 11, 2017)

dlane said:


> Purge with argon real good , I knew a guy that cut them all the time by running his car exhaust thru the tank for a half hour. With that said I made my forge from a portable air tank , no fumes


I have Argon. Just picked up a second tank as a matter of fact.I also thought about buying 20 feet fuse and give it a test out in the back 40. Just to be sure!


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## MozamPete (Apr 12, 2017)

Fill and empty with water a couple of times to flush out any gas. I still dropped a lit match in as a final check - standing well aside from the hole - prior to starting cutting just to make sure.

My build is here if your interested http://www.hobby-machinist.com/threads/furnace-project.35359


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## RJSakowski (Apr 12, 2017)

If you fill it completely with warm water with an ounce or two of detergent added, you will flush essentially all remaining volatile propane.  Propane has ethyl mercaptan added to give it the stink and it will settle out as an oily liquid which can have some propane dissolved in it.  When cutting a tank with a torch, the oxygen introduced when the tank is pierced can cause a flare up or possibly even a small explosion from this oil.
If you are concerned, you can fill the tank with water when you are cutting with the grinder.  It will be messy but the chance of a fire will be virtually nil.


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## f350ca (Apr 12, 2017)

I've used the fill with water method a couple of times and I'm still here. Shake a bit every time I touch the grinder to the tank though. I read somewhere that a little bleach in the rinse water will help neutralize the ethyl mercaptan. I tried it and it seamed to. I repurposed one as a hydraulic tank, it took a lot of super clean to dissolve the oily residue.

Greg


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## ericc (Apr 12, 2017)

I'm not sure that this is much safer, but I saw an old blacksmith do it in the following manner.  He heated a piece of coil spring to forging temperature and made a hack tool out of it.  That is a wedge with a tapered shank wrapped as a handle so as not to transmit vibration.  It was air quenched and tempered to straw.  When struck on the broad part of the wedge, it will slice right through sheet steel.  This may spark, but a lot of blacksmiths do not think that tempered steel draws many sparks.  I once participated in a charcoal retort building workshop where there was no power, and this was much preferred to using a torch or a hacksaw.


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## dlane (Apr 12, 2017)

The guy that cuts a lot of them ( 5gal to 200 gal ) told me the most important thing is to get all the oxygen out . He used a plasma cutter , I would make BBQ's out of them after he made a couple cuts on them , I wasn't that brave


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## Tony Wells (Apr 12, 2017)

Just stick an open ended air line from your compressor down into the tank and let a fair amount of air flow through the bottle. As long as you keep the air/fuel mixture below the LEL you are safe. I used to weld and solder gas tanks that way quite a bit, even fresh off the car. If the mixture you create is too lean, it will not ignite.


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## Ski (Apr 12, 2017)

Thanks guys. I appreciate the tips. Will post an update but probly a couple weeks out. Ski


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## DAT510 (Apr 12, 2017)

When cutting gas tanks for EFI in-tank pump conversions we would fill the tanks with Dry Ice.  CO2 is heavier than air so it won't float away and as the dry ice sublimated, it would provide a continuous flow of CO2 to replenish any lost from cutting/etc while pushing out any flammable gases.


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## easttex (Apr 12, 2017)

Argon is kind of expensive for a purging agent.  I'd use CO2 or engine exhaust to clear a tank for welding.

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## LotsaChips (Apr 16, 2017)

Two years ago I built a large smoker for my nephew. The smoker would be built from a 250 gallon propane tank. Even though this tank had set for years with the valve removed I was quite nervous about cutting into this tank. Since this would be used as a smoker it was critical to get rid of the mercaptan. I used 50 gallons of water, 5 gallons of bleach and 1 gallon of Dawn dish detergent. Let it set for three days, rolling the tank occasionally. 

With an overabundance of caution, after I drained the tank, I removed the bottom drain and put a shop vac hose in the valve hole on top of the tank 
and purged it for thirty minutes. I then made a fuse with a paper towel and put this sticking out of the valve hole, then lit it and got the hell out of the way. 
No explosion! Then I went to work with my plasma arc torch.


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