Originally Posted by Pablo83
I used a thin disk on a 4-1/2" angle grinder to cut it.
I had to make sure ALL the fuel and vapors were out before welding it; it was a bit of a process. First I emptied all the fuel and sprayed compressed air through it. Then I let the tank sit in the sunlight for an hour or in the shop overnight to evaporate most of the leftovers. There was usually still about half a teaspoon of fuel left in it at this point so I would shake it up good and hold a long nose lighter to the cap
and wait for it to go WHOOOOSH
. I would repeat the shaking and lighting until it would no longer light. It was usually ready for welding at this point, but I still needed to make sure the tank cap opening was not pointed at me when I started welding. Fun stuff.
Someone once told me to connect a long hose from a car exhaust to the gas tank you want to cut/weld, and run it for a while. Apparently, all the exhaust fumes burn any remaining fuel and vapors without explosion because of the high CO2 content in the exhaust fumes. I'll be giving it a try on my next project.