I have been TIG welding a Pitts S1 fuselage for the last couple months and for the most part I could not be more pleased at the results. However, when I was welding the left side seat bottom tube to the small (about 3") support tube I ran into a very stage phenomenon. I had cleaned both ends with a sandpaper "flapper" and I ran an acetone soaked rag down the inside of the tube as well as wiping down the outside. I had tacked both ends as well as the support tube with no issues. I even fully welded both end of the tube just fine. When I went to fully weld the support tube the puddle was moving along nicely and then I heard a "POP" and the side of the puddle, not even the hottest point, had blown out! 
I though maybe I stepped on the gas hose and stopped my shielding gas so I carefully closed the hole up and went on my way only to have it happed again and again.
I was able to move on to other joints and weld them up just fine so I don't think it is the welder or my gas. I have come to the conclusion that the pipe will need to me removed and a new one put in its place but I have no idea what could be causing the issue.
Any and all thoughts are welcome.
Thanks,
Dan
I though maybe I stepped on the gas hose and stopped my shielding gas so I carefully closed the hole up and went on my way only to have it happed again and again. I was able to move on to other joints and weld them up just fine so I don't think it is the welder or my gas. I have come to the conclusion that the pipe will need to me removed and a new one put in its place but I have no idea what could be causing the issue.
Any and all thoughts are welcome.
Thanks,
Dan
