seeking any and all advice

We are tig welding 1018 mild steel tubing together with another 1018 tube that has had a solid lug soldered to it approx. 3inches from the weld zone. We are getting weld porosity in the center and edges of the weld. The flux we are using is high temp black flux. We are trying to clean the flux out of the pipe but some residue remains. WE are using ER 7OS-2 tig rod. Any advice is welcome,

Thanks
Kling

can you weld before soldering?
can you use another type of flux which can be more easily removed?
have you used acetone or similar to try and clean it?
are you using enough shielding gas AND purging the inside of the tube?

If I had to guess, I would say you are not purging the inside of the tube and that is your biggest problem.

Matt

Thanks keebler for the help, we are trying a few of your suggestions.