Copper and brass pipe and fittings are typically soft soldered using low melting temperature alloys, but in some circumstances joint connections made in these materials must be brazed. Brazing is similar to soldering except the filler alloy melts at a much higher temperature; usually between 590C - 815C (1095F-1495F), as opposed to soft solder which will typically melt between 175C - 290C (350F - 555F).
The two main types of brazing alloys plumbers will be required to use can be seen below:
BCuP brazing rods containing copper-phosphorus.
BAg brazing rods containing silver.
A brazed joint will be capable of withstanding higher pressures at higher temperatures than soldered joints and may be required by code for the plumbing systems listed below:
- Underground joints in a water service are often brazed, but may also be flared or compression. Soldered joints are not permitted underground. Under a building, only compression or brazing are permitted to join copper.
- Joints made on extracted tees must be brazed. An Extracted Tee is a method by using a specific tool (Pipe Extractor) to create a hub or fitting-end directly onto the copper pipe itself. Once completed, the other pipe end can be inserted inside the extracted end, and then brazed.
- Joints made on medical gas piping must be brazed with a constant flow of inert gas.
Making a Brazed Joint
- Cut and deburr the copper pipe.
- Clean off the oxidation on the pipe end and inside of the fitting socket with sandcloth or a fitting brush.
- Apply a thin film of brazing flux to the fitting and pipe.
- Begin heating the joint with a high heat gas (Acetylene). Ensure to keep the torch moving so the base metal is not melted.
- Apply the tip of the brazing rod to the edge of the fitting just behind the moving torch tip. When the filler rod begins to melt, capillary action will wick the filler into the socket. Work your way around the copper joint until you have brazed the entire circumference.
The video below gives a pretty good explanation and demonstration of how to braze a copper joint, enjoy.