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HVAC and Plumbing Distributor
Anthony Coker

Anthony Coker

Technical Services Manager
North Georgia District

Soldering, Brazing, and Welding

In this article, we will go over a few differences between the types of metal-joining processes used to connect pipes together. Without these processes, we would not be able to move refrigerant to any components such as steel pipes on a chiller or copper pipes on a residential air conditioner. We may have to make field modifications to attach them together in the field or just to replace an item such as an evaporator coil. That is why it is important to know the various techniques used in today’s industry. Remember: safety is first and foremost. Always wear safety glasses or a face shield when brazing or soldering. Gloves should always be worn to protect your hands. If you are in a confined area where there are a lot of fumes or smoke, then use a respirator.

Soldering

Soldering is the process of joining two pieces of metal together. You will need solder, flux and a heat source for soft solder. For this example, we can use a propane torch. This is what a lot of plumbers use to plumb your house for water.

You will need to clean both pipes on the outside ends and deburr the inside of them to make sure there are no objects that can break free in the pipe and cause clogging or issues with the operation of the refrigerant cycle. Now we clean the inside of the fittings as well, typically using an emery cloth or sand paper. After cleaning all surfaces by sanding, you will want to wipe them with a cloth to remove any residual debris. Then, you will need to put the flux on the areas you cleaned and connect them together with the coupling. Now that they are together we can solder them.

Flux paste cleans and assists in the bonding of the solder to the pipes. When you solder you will need to heat the fitting in the middle as to draw the solder into the fitting. The fitting has to be hotter than the pipe. If they are the same temperature, the solder will not flow inside or wick into the fitting between the pipe and the fitting; it will just drip onto the ground. If that is the case, cool the pipe down with a rag that has been wet with water and then try again until it is right.

Applications for solder are as follows: Refrigerant lines that will not exceed around approximately 200psi when using 50/50, which is 50% tin and 50% lead. This will work for low pressure refrigerant and non-potable water (not drinkable).

95/5 solder is 95% tin and 5 percent antimony and can be used for drinking water applications. 95/5 is stronger as well for HVACR applications which can handle pressures up about 275psi. Now there is a lot more involved than this. This is just an informative view. Other variables include pipe strengths, tensile strengths and types of copper you are using. “Example: type k, l or m which is a rating of copper pipe for wall thickness changes the maximum pressure each can handle. The lowest of the three is M and the highest is K. But it even has an annealed version and a drawn which changes the pressures as well.

soldering

Brazing

Brazing is the process of joining two metals together without the wick effect that solder has.

It consists of two similar metals or dissimilar metals being joined by a brazing rod that melts before the metal being joined will. This will help assist in the bonding process. You can butt the two pieces together and braze them and it will be stronger than a soldered joint. The copper pipes can get red and silver solder will already be melted at this point.

Now a few other terms we must be aware of:

Liquidous temperature is the lowest temperature at which a metal is liquid.
Solidus temperature is the highest temperature at which the metal is completely solid.
The temperature at which metal melts is called its melting point.

Brazing uses a higher temperature to melt the rods than soldering. Gas torches such as MAPP gas or oxy acetylene could be used depending on the environment and the size of pipe. MAPP gas works well in non-windy areas for up to ¾ inch pipe. Anything larger than that would push the limits of the heat.

In brazing, the components that make up the rods is determined by the metals you want to join. For the HVACR industry, we typically use silver solder containing different percentages of silver. This will determine the fluidity of the rod on the metal being joined, the cleanliness of the joint for aesthetics, and the strength of the joint.

Flux can come in various forms such as a paste or a coating on the rods. In the example for the HVACR purposes we will use 15% silver solder. An example composition of 15% Silver Solder is: 15% Silver, 80% Copper, 5% Phosphorous. In joining copper to copper, none of these phosphorus/silver/copper rods need flux or would even benefit from it. The phosphorus allows the rod to self-flux on copper. So, if you use the silver solder it has phosphorus in it and does not need flux. It is the flux!

Example: Two pipes cleaned and placed inside a coupling. Heat the pipes until the 15 percent silver solder melts and spreads smoothly along the metal joint between the pipe and the coupling. Then do the other pipe at the joint at the coupling as well. Then stop and allow to cool. Or use a wet rag to cool it down.

brazing

Welding

Welding is the process of melting the two metals together and is the strongest of all joints. It can be used on various metals and there are several processes that go along with this as well but we will stay within the HVACR industry needs.

Welding comes in various forms such as MiG, TIG and Stick Welding. There are others but these are the main ones.

MIG is a form of wire welding. TIG is a form of a high frequency welding which melts the metals together or melts the filler rod to the metal to fill the void between the two pieces of metal. Stick welding uses a flux coated rod that comes in contact with a grounding clamp from high current. It produces an arc, which starts the melting process of the fluxed filler rod in the midst of the two pieces of metal.

In the HVACR industry steel pipes are used for industrial equipment with large pipes such as chillers. The pipes are welded together at the factory but if there was ever a leak in one you would have to weld it. Not your typical daily function, but it can be done. It is probably the least used metal-joining process from a technician’s point of view but it is still used.

welding

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