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