butt welding exhaust system

I keep my joints as tight as possible. wire speed up, heat down.....no hurry. Always have beautiful joints that can be ground off or left as is. Aluminized exhaust pipe can be tricky. If you leave gaps at the joint you will get a kind of "sugaring" on the inner surface.

Buy some pipe and practice before you start on your project. Something else MAY work better for you.