Heard of that too, common with diesel fuel tanks.
But i did work with a welder that had a fuel tank explode too.
When i think of welding a gas tank i remember him. Not going to happen.
Clean tank,hot soapy water and dried in the sun. Then i will weld it.
We had a family friend killed when I was just around 10-11 years old. He was trying to weld on an old propane tank. It went boom. He supposedly had opened the valves and thought it was empty but it had enough to ignite