[TheForge] cutting propane cylinders- fuel-air mixture

[xlch58 at swbell.net]

You don't have to get that fancy in the analysis. No one cuts up brand 
new tanks unless your a government contractor.   Take a look at the 
inside of an old compressor tank, gas tank or whatever.  They have a lot 
of rust, which does readily absorb stuff.  If they are really old the 
rust is scaling and there may even be a pile of it in the bottom of the 
tank.  On a really big tank there will bits of leaves, something that 
looks like a dead rat. On a really big tank you might find bits of 
mobster -- oh never mind , that is just another rat.   Some tanks are 
lined and the lining seperates with age and fuel will seep through 
capilary action behind the lining.   So accept that you will never get a 
tank empty, since steam cleaning them doesn't always work.  And 
personally I wouldn't fill one with water for several reasons, mainly 
because I have never had luck completely filling any tank with anything, 
so all I might be doing is washing more volatile liquid loose and then 
concentrating it in an air pocket where it reaches a concentration that 
will support combustion.  I know filling it with water feels right, but 
I would personally go with exhaust gas.   

Charles

Ralph Sproul wrote:

>Bob, I think it depends greatly on how good your towel  and your scale
>are.......
>
>A metal surface is not perfectly smooth and things dry/adhere/stick to it.
>When you take a piece of tank that has been cut apart (like a 275 gallon
>drum - which I'd cut with an air chisel, as it'd take to dam much C02 to
>approach it with a torch)........ then you heat the metal with a torch - the
>first thing that comes is condensation........but then you'll notice the
>blue/yellow streaming colors (on that water from condensation). As the water
>vapors off and you have the smoke which is the fuel mixing with
>air.........this is what will kill you if you do the torch thing.  The fuel
>smoke mixes with the air, the metal heats up, the container goes off (that's
>in the preheat stage).   If you really go for it and test the tank by laying
>into the oxygen stream of a cutting torch - you severely speed up the
>process of fuel air ratios with the oxidizer.
>
>If you see an open section of tank skin some time - try it.  Oil/fuel that
>is.  I'm not sure about propane (which is the topic header) - as I've never
>torched one of those - or cut one open or used it for a forge.........I use
>pipe instead.   That elliminates a lot of doubts.   :-)
>
>Not that any tank is made of cast - but cast is extrememly
>pourous.........and it's why the oil or pitch soaked castings are so
>miserable to weld.  Steel is a far cry from that type of porous, but the
>surface of the tank gets a coating of the fuel that dries on there.  This is
>what keeps the inside of tanks from rusting for so long.
>
>I did see some metal pictures from under a microscope in a metalurgy text
>once.  It appeared there were "poures".........maybe fuel "sweating" off the
>metal skin is a better way to put it............could you live with that?
>
>Ralph
>  
>