Don't want to make a bomb!

I am going to be attempting to pull the dents out of my tank using a stud welder. What is the best way to ensure that all gas fumes are out of the tank before I start? I really don't want to blow myself or the tank up. Thanks for all suggestions in advance.

 

flush it out. let it dry a few days. leave it open while drying. there were other tips i forgot, but those are pretty common sense ones...

 

What should I use to flush it out?

 

You have a couple of options:
1. (cheap and available) Pipe car exhaust into the tank to void it from combustible fumes. Won't rust the tank like water.
2. Take it to a radiator shop and have them boil it out. This will ruin the paint but you won't have any fumes left to ignite.
3. Fill the tank with CO2 or other inert gas (expensive and a bit difficult depending upon your resources).
When prepairing the drop tanks off of aircraft, we were required to positive vent the tanks for a day or two(compressed air for a very long time). You don't want ANY fumes left in the tank when you strike an arc near it.

 

I've done it many times, as a qualifed fabricator/welder I fill the tank with soapy water and leave it overnight, drain and weld happily.
I do the same with LPG cylinders when converting them into wood burning stoves.

 

At the Body Shop near me ... they do this.

Hook-up a Shop Vac's EXHAUST to the Tank's Filler with the Hose Taped in the Filler and the Tank Venting through the Petcock.

20 Minutes.

 

Thanks to everyone for the suggestions. I wish I had a shop vac. Kinda hard to believe that I don't. I seem to have everything else.

Jay~Dub, doesn't your method lead to rust in the tank?

 

Actually all you have to do is plug all the holes and drop some dry ice in it. You can leave the gas in the tank. The dry ice takes out all the oxygen so there is nothing to ignite. Emptying the tank makes it more dangerous since fumes are more ignitable than liquid gas. It is an old welders trick.

Putting water in it will make it rust in a hurry!

 

If you use the hot soapy water trick... rinse it out with half a bottle of methylated spirits, this drives out the moisture... Just leave it over night to dry.

 

What is methylated spirits and where do I get it?

 

4. Get kid brother to drop a lighted match in while you stand well away.

 

Can you perform the stud weld while there is water in the tank? Ive heard of guys welding automotive fuel tanks while they were full of water.

Also, one time I had to remove a section of a fuel tank to return to the manufacturer for inspection. I kept the tank full of water while I cut the section out with a cut off tool.

 

I thought about keeping water in the tank while I do it which would also keep the metal cool. Just worried about rust.

 

There is an "Old School" technique.
It's called the Old Vacuum Variant.

You take that Old Vacuum Cleaner that held together with Duct Tape and put the Vacuum Hose right in the Gas Filler Neck.
No need to tape it, really.

Do it outside.
Use a long extension cable to get it away from any windows.
Turn-on the Vacuum but don't plug it in until you have stepped-back some.
Plug in the Vacuum.

The Test results are Immediate.
If the vacuum is still running and venting-out the tank, ...
The Tank is safe to weld.

If there's and flames coming-out of the Vacuum Cleaner after the Electric Motor is energized when you plug it in ...

That's why you use the OLD Vacuum.

 

I think I will leave your method for someone else to try, Rick. LOL