Quote Originally Posted by DiabolicZ View Post
Gotcha, so it leaves something similar to a glass bead after it has melted inside the tube. Wonder if you can just smack the tube and get it to flake and fall out or if you have to actually grind it out?
I have used this and no just smacking it will not remove it. It is some tough stuff but works well. Kind of reminds me of the flux on a stainless rod for stick welding, but all ground up.

RESIDUE

The thin glass-like residue is chemically inert after welding and adheres tenaciously to the base metal. While this residue is unattractive to the eye, it does not affect the quality of the weld and usually need not be removed. However, if removal is desired, it is easily accomplished with a stainless steel wheel, stainless steel brush or common pickling compounds. Our research indicates that 'Wonder Gel', manufactured by Bradford DeRustIt Company is excellent.

(Note: there are some pipe or tube welding applications where absolute purity and a polished inside surface are required. These include food or beverage lines where subsequent product refining will not take place, medical oxygen lines, computer chip manufacturing air lines, and high service temperature (above 1000°F) steam lines. In these situations we recommend purging instead of SOLAR FLUX so as to avoid a difficult chemical cleaning process.)