QB – Brazing Qualification: Procedures and Performance
Where brazing begins
Section IX treats brazing separately (Article III) because the physics differ: the filler metal melts, the base metal does not. Section IX defines brazing as joining with a filler metal whose liquidus is above 840°F (450°C) and below the solidus of the base metals. Below that temperature the process is soldering, outside Section IX; above the base-metal solidus it is welding. Expect a definition trap built on those two boundaries.
Procedure qualification (QB-200)
A brazing procedure specification must be supported by a brazing procedure qualification record produced from an actual test assembly. The essential variables are not the welding list. They include the brazing process and heat source, the brazing filler metal, the flux or protective atmosphere, the joint clearance range, the brazing temperature range, and the time at temperature. Joint clearance is unique to brazing - capillary flow depends on it - so treat it as essential. When notch toughness is specified, supplementary essential variables such as heating and cooling practice become essential.
Qualification tests follow the joint type: tension and peel tests for common lap and butt configurations, and sectioning for tubing and small assemblies. Variables and results are recorded on the qualification record.
Performance qualification (QB-300)
Brazers and brazing operators qualify by producing a test assembly that is examined - visual examination plus sectioning or peeling as applicable - to show sound joints, complete filler-metal distribution, and no voids or excessive erosion. Brazer essential variables cover the process, the filler metal, and the thickness and configuration ranges tested. Continuity mirrors welding: qualification lapses after six months without brazing with that process (QB-322).
Rule of thumb
In brazing, the filler metal and the joint clearance do the work. Change either and requalify the procedure; change the person's process and requalify the brazer.