
Originally Posted by
jakeru
Looks like a great project for learning to weld thin stainless tubing to me.
The fit-up must have been very good if you welded all that autogenously. If you don't need maximum strength of a "built-up" weld bead, there is nothing wrong with autogenous welding, imo. Welding autogenously can allow dramatically increased travel speed and along with that, a reduction in heat input.
It is challenging to maneuver around a tube. You will find with additional practice, you will be able to get around the tube with fewer "stops and starts". i.e., you'll be able to weld longer seams at a time, and pivoting your torch (filler rod if applicable), and point of view more each time.
The solar flux when it gets up to temperature, melts and shields the stainless underneath, and then solidifies into that black glassy stuff you see on the inside of your tubing. Assuming you got the solar flux evenly applied everwhere on the back side of the weld, then if you see a spot on the inside of the tubing where the solar flux didn't get up to temperature (no black glassly stuff but you still see the grey powder of the unactivated flux), it means you didn't achieve enough heat to melt the metals and fully penetrate the weld bead through to the back side in that spot.