I am working on a project inside of a house. There are three pipes 18"dia 1/4" thick 90" long. I will be welding them together.Once the pipe is welded,there is going to be a tank 40"dia 5' tall. I plan on doing all the welding using a dry line.I have a Dynasty 300 my question is how long can I weld before I have to stop to let the lines cool off? thank you