hacking handheld propane cylinders

[Mcgyver]

always a good idea to avoid blowing oneself up......there was a thread recently on how to purge larger propane tanks so they can be machined or otherwise worked....anyone know how to safely set up the small hand held bottles for machining etc? basic instructions sought!

thanks

[barts]

Propane flammability limits are narrow (2 - 10% approx), so the easiest thing to do is to drain tank completely w/ propane torch or equivalent , and using an adapter fitting, repeatedly fill cylinder w/ compressed air and then discharge completely in open air,

After 3 or so cycles, you're completely good to go. You can weld, machine, plasma cut, etc. If you're nervous, try igniting the air discharging from the empty cylinder.

It's much easier/safer than purging a gasoline tank, since the liquid propane all turns to vapor when you empty the tank.

- Bart

[Evan]

Or you can put in a bit of water and boil it for a few minutes. This will purge the propane and also any oxygen by replacing it with water vapor until it cools down.

Or, dump in a few tablespoons of bicarbonate and a 1/4 cup of vinegar and it will fill with CO2. Pour out the slurry and plug the hole to keep the CO2 inside. No bang.

Or, leave the tank open (drill hole?) and let sit for a year or two.

Or, fill it with some ethanol and slosh it around. Pour it out and rinse with water. Propane dissolves in ethanol and will be rinsed out along with the ethanol.

[barts]

Or you can put in a bit of water and boil it for a few minutes. This will purge the propane and also any oxygen by replacing it with water vapor until it cools down.

This reminds me of one of my favorite demonstrations for kids; take an empty aluminum soda (pop) can and put a bit of water (a couple of tablespoons) in it... now heat the bottom of the can (a gas stove or propane torch works well) until the water is boiling... using a pair of hot dog tongs, in one smooth motion invert the can into a open container of water. It will instantly collapse as the steam from the boiler water (which displaced all the air) condenses back into water, creating a vacuum. Air pressure then does the rest; the opening at the top of the can is too small to allow the water to be drawn in fast enough to prevent the can from collapsing...

[Your Old Dog]

If you're nervous, try igniting the air discharging from the empty cylinder.

ROFLMAO ! Kowalski is that you?

[Evan]

This reminds me of one of my favorite demonstrations for kids;. . .

Yeah. It works well. It's amazing how much air really weighs.

[pressurerelief]

You should not purge anything flammable with air since you will have a flammable mixture inside the vessel at some point. This is actually prohibited by DOT, the agency having jurisidction. Inert gas or CO2 is ideal and keep the cylinder with the valve down while purging a gas with a vapor density greater than one. You can actually layer gases in a cylinder via vapor density. It does not just mix as alot of people assume.

I work on gas cylinders and have a new customer that use to purge with an air compressor. He blew the side out of a cylinder via a flammable mixture and static electricity. I do all of their cylinders now that he has his shorts cleaned out.

The rail car picture is from steam cleaning and the last one off the top closed the manway and let it cool. OOPS

P/R

[tony ennis]

What surprised me was how quickly it can happen.

I figured it would be slow, even for an aluminum can. Nope!

55 gal drum...

Another 55 gal drum

And for completeness, here's the train car pictured above getting crushed!

[Alistair Hosie]

Fill the tank with malt whiskey twelve years old and send immediately to his lordship. Alistair

[SGW]

I made a tool to unscrew the valve (it's like a tire valve). After unscrewing the valve, I've let the cylinder sit around going through temperature changes for a while (a couple of weeks) so it can purge itself.