Overheating inside of tube during fillet brazing

[cmsanford88]

Hey guys! Been practicing my fillet brazing for fun. I'm still working on heat management and not taking forever, but I feel like I can get he material roughly where I want and not cook the flux in the process.

My question is about the interior of the tubes. Any joint I finish has some scaling or flakes inside. I'm assuming it's just too hot for too long in there. Is this something I need to totally eliminate to consider the joint safe, or is it just par for the course when you're working at brass temperatures?
IMG_4289.jpgIMG_4288.jpg
Thanks
Chris Sanford

[cmsanford88]

Another stab today that just generally looks like a better braze, still the same flaking inside though. IMG_4290.jpg

[Curt Goodrich]

Are you fluxing the inside of the tubes?

[cmsanford88]

Nope, and now I feel deeply foolish