How to Braze Pipes: A Guide to Brazing in Plumbing
Nov 17, 2021
When it comes to joining two pieces of metal pipe, plumbers often choose between brazing and soldering. Both methods require a torch and a molten filler metal, and some other specialized tools. Though the techniques are similar, soldering is much more popular. Brazing is a useful skill for plumbers to know so they can work with high-pressure lines, and is also a good skill to know for HVAC and refrigeration specialists working with gas pipes.
What is brazing in plumbing?
Brazing, also known as silver brazing or silver soldering, is the act of joining two pieces of metal with a molten filler material known as a brazing filler material.
First, the plumber cuts, cleans, and prepares a pipe and a fitting for brazing. Then the plumber uses a torch to heat the pipe and fitting to a very high temperature. Once sufficiently hot, the plumber touches the copper joint with the tip of a brazing filler material—a stiff rod made of different metals (typically made from copper, nickel, and silver). The heat of the metal surfaces melts the braze alloy, which then flows into the joint. If brazed properly, the brazed joint will be gas and liquid-proof once the brazing filler material hardens.
Like soldering, brazing does require flux, though it is often part of the brazing filler material. After brazing a joint, the plumber purges the system with nitrogen to remove the flaky oxidation left behind from the joining process.
The brazing process is typical in refrigeration or HVAC scenarios, but it can also join plumbing pipes, such as copper to copper joints or brass for water transportation.
How does brazing work?
To understand how brazing works, there are a few principles with which to become familiar. Note that brazing might seem similar to TIG welding, however in welding both the base metal and the filler material melt. When brazing, only the filler material melts, leaving the base materials intact—this molten filler metal creates the seal.
The phenomenon that allows molten filler metal to flow into the joint rather than just spill to the floor is capillary action. Capillary action is the result of molecular surface tension, where the liquid is drawn up through a narrow space. This is what occurs with the molten filler metal and the hot pipes being brazed—the surface tension and molecular adhesion between the liquid filer and the pipes draws the liquid metal into the joint.
Brazing Temperature Control
Compared to soldering, brazing requires much higher temperatures. In fact, the melting temperature of the brazing rod is an excess of 842 degrees Fahrenheit (as opposed to 450 to 500 degrees Fahrenheit for a solder). An acetylene torch can easily heat metals beyond this temperature, allowing the brazing filler metal to melt and the base metals to remain intact.
However, an acetylene torch can also heat the base metals past their melting points. If the brazer isn’t careful, they can warp the pipes and fittings, or cut through them all together. For this reason, it’s important to heat the metals enough for free-flowing brazing, but not constantly for extended periods of time. Doing so can lead to warps and leaks.
4 Ways to Braze Pipes
1. Torch Brazing
In torch brazing, the plumber uses a handheld acetylene torch to heat the base material (typically copper or brass). Once the joint is hot enough, they’ll introduce the brazing rod to the joint, allowing it to melt between the metals. Once the molten filler metal cools and hardens, it creates a solid joint.
Torch brazing is the most common method of brazing used in plumbing. It’s highly portable, and the brazed joints that result from the process are incredibly strong.
2. Induction Brazing
Induction brazing is similar to torch brazing except that instead of a torch, a machine produces electric induction heat. The machine never touches the workpieces, which is a distinction from other types of brazing. This process is popular in controlled atmospheres like manufacturing settings. Though the machines are large, they heat metals very quickly.
3. Furnace Brazing
In furnace brazing, technicians place small pieces of brazing filler material across the material at each desired joint, and the entire workpiece enters a furnace. Once the material reaches the correct temperature, the brazing material automatically melts and flows between the joints. Furnace brazing requires specialized furnaces, a controlled atmosphere, and typically, a conveyor belt, hence this type of brazing is typically performed in industrial manufacturing plants.
4. Resistance Brazing
In resistance brazing, a technician applies an electrical current to the base material. Due to the base material’s resistance to the current, it becomes hot. Once hot enough, the brazer fills the joint with the brazing filler material. This method requires large equipment, so it’s best for manufacturing settings.
What tools do you need for brazing plumbing pipes?
Brazing plumbing pipes requires a special set of tools. Fortunately, most of the following tools work for brazing and soldering, allowing for a bit of flexibility: