Good evening all.  I'm new here and first time poster.  I work in a facility that brazed a lot of copper for HVAC applications.  Recently, we experienced a rash of problems with a copper colored powder buildup inside the tubing at the braze joints.  The only change in our process was a change in the torch and a new "gas flux" system.  With this new torch and gas flux system, it's hard to tell when the copper is too hot.  I'm curious if something chemically is happening to the copper inside by getting it too hot.  If you get it too hot will it cause this powder to form on the copper inside?  This is brand new copper tubing and always cleaned to shine like a mirror with just a lint free cloth before brazing.  No cleaners are used or any other substance.  Thoughts?

Sounds like a good reason to qualify the process to verify the mechanical properties are still being met.

Al