HVACR Pipe Soldering Brazing – Refrigeration Systems

HVACR Pipe Soldering Brazing - In HVACR there are two major types of soldering done. Soft Soldering for soldering water pipes and brazing or silver soldering for soldering refrigeration piping. There are various techniques for both types of soldering and everyone develops their own in the field but it is important to follow the basics of soldering when joining the piping together. Following the basics of soldering will ensure success and we all enjoy a successful job completed.

As always safety is first with anything. Two big considerations must be adhered to when soldering or brazing:

• Eye protection and burn protection for hot dripping soldering. Keep yourself safe when soldering or brazing.
• The inherent risk of using an open flame around combustible materials. Always make sure you have a plan and use preventive techniques such as wet rags and fireproof clothe or barriers. This is especially true when soldering around wood or even outside (around a condenser) where pine needles or leaves can easily catch fire and spread rapidly. Always have either a hose or fire extinguisher handy.

HVACR Pipe Soldering Brazing - Refrigeration Systems

Soldering Pipe with Leaking Valves

Every plumber and many HVAC technicians have had the privilege and frustration of attempting to solder a copper water pipe that has a leaking valve that prevents the complete shut off of water flow. These plumbers and technicians know it is impossible to solder copper water pipes that have water in them or flowing through them. The water has to be drained from the pipe and the pipe must be dry and clean before soldering can begin.

So if we have a valve that won’t hold the water back or even piping systems with the water shut off valves but have piping running up multiple levels with no isolation and the water keeps migrating back to where you want to solder, how do we keep the water from the location where we are soldering?

The Bread Trick

Plumbers and HVAC Technicians have used this age-old proven method to stop the flow of water where they want to solder. Simply take some white bread, remove the crust, and roll the bread into a ball as appropriate to the size of the pipe. Stuff this ball into the pipe where the water is coming from and solder the joint. The bread holds the water back while the soldering is being done.

After the soldering job is done and the water flow restored the ball of bread will dissolve and complete water flow restored especially after the strainers are cleaned. Don’t forget to clean the strainers if the system is equipped with strainers. This does not work when the pipe is under extreme pressure.

Pipe Freezing Machines | HVACR Pipe Soldering Brazing

HVACR Pipe Soldering Brazing - Another method for stopping the flow of water if a valve is broken is the pipe-freezing machine. This method is far more expensive than the bread trick but it works flawlessly. Simply clamp some refrigeration heads to the pipe in question and turn on the machine.

Spray some water on the refrigeration head and wait the recommended time required by the manufacturer of the pipe freeze machine. Then perform the soldering job and unhook the machine when finished. The ice inside the pipe will melt and the flow of water will be restored. The water pipe freezing machine is a good way to solder pipe where it is otherwise impossible to shut off water flow.

Brazing and Soldering Copper HVACR Pipe

Refrigeration piping is always brazed as brazing makes a very solid leak-free joint that withstands high and low temperatures and pressures. Brazing is done with oxyacetylene for refrigeration and the oxyacetylene tanks should have pressure regulators for regulating proper pressures when brazing. When soldering refrigeration pipe it is best to use solder which has a composition of silver in it as the silver bounds with the copper and makes for an excellent leak free strong joint (capillary attraction).

Very High Temperature – Brazing

Brazing in HVAC is done with oxyacetylene torches which heat the pipe to temperatures approaching 6,000° F. While most solder will melt far below this temperature it is important to be careful when brazing. It is important to note that all safety precautions should be applied when brazing HVAC pipes including safety glasses and fire extinguishing equipment. Safety is always first when doing any job in HVAC and especially when dealing with oxyacetylene equipment and brazing. 

As defined by the American Welding Society it is considered brazing if the melting point of the solder alloy (filler metal) is above 842° F and it is considered soldering if it melts below that temperature.

Clean & Flux with Any Type of Soldering

There are many types of solders available for both soldering and brazing and each different type has its own flow rate or melting point. Each different type of solder may require flux and some may not require flux. Always begin with the clean pipe. Protect the pipe to make sure nothing gets into it before soldering or brazing. Cleanliness is an absolute necessity, especially with refrigeration.

Never leave the end of the pipe unprotected. Use tape or a plug to plug the ends so nothing can get into the pipe including trash, debris, or moisture. When outside, avoid at all possible cost brazing refrigeration piping when it is raining. Moisture is an enemy to modern refrigeration systems. It is good practice to always use flux as the flux prevents oxidation.

Oxidation | HVACR Pipe Soldering Brazing

Oxidation will leave residue inside the pipe unless proper brazing and soldering techniques are adhered to when joining piping. As noted below, a nitrogen flow will also reduce the possibility of oxidation and reduce the possibility of residue left inside the pipe.

In refrigeration piping, as well as other types of piping that serve mechanical equipment, it is very important to properly cut the piping. Never use a saw such as a hack saw. Use tubing cutters to make a smooth even trimmed end on the pipe. In some cases, you will also need to ream the pipe to get rid of rough edges. Always ensure you clean the pipe inside and out thoroughly. Little bits of copper can damage mechanical equipment and cause failures.

Stated once again, make sure the pipe is thoroughly clean with no dirt, debris, moisture, or metal bits inside the piping. Clean piping is crucial to proper installation including the process of assembling and brazing the piping.

Pipe on the left is clean because nitrogen flow was used while brazing. The pipe on the right has black flakes inside it because nitrogen was not used.

Before brazing or soldering any pipe it is important to fit the pipe and clean it. This brazing setup will ensure the job is done correctly. Cut the pipe to the desired length with tubing cutters and ensure it has a good fit. After checking the fit and proper length clean the area where the pipe is to be soldered.

Flux | HVACR Pipe Soldering Brazing

After cleaning apply flux to the inner and outer joints. Using a nitrogen bottle with a very slight flow of nitrogen allows the nitrogen to flood the pipe flushing any oxygen from the pipe. Maintain a slight flow of nitrogen in the open refrigeration circuit until you are ready to perform a triple refrigeration evacuation. The nitrogen prevents oxidation inside the refrigeration piping.

It is important to apply the heat evenly across the joint and heat the pipe before applying the solder. After the pipe has been heated apply the solder to the joint and allow it to melt into the joint. Do not use the torch to heat the solder but use the heat on the pipe to melt the solder evenly. If done properly the solder will seemingly be sucked into the joint. That is called capillary attraction and is the target or desired goal of soldering or brazing.

Do not use too much solder because the solder can migrate inside the pipe and cause a blockage of the pipe or little beads of solder may form inside the pipe and these little beads of solder will migrate through the refrigeration system and plug screens, metering devices, and possibly damage the compressor. Do not use too much heat as you could melt the base metal which is the copper pipe you are trying to join.

The Nitrogen Pressure Test - HVACR Pipe Soldering Brazing

After the pipe is soldered and complete apply a wet rag or water to the joint and thoroughly inspect the joint for even solder around and inside the joint. Use a mirror for difficult-to-see joints. After the inspection is complete and you are satisfied that all solder joints are completely sealed perform a pressure test with nitrogen to check for leaks. Use soap bubbles when the pipe is pressurized and look for bubbles around the newly brazed joint. Also, watch the pressure gauge for a drop in pressure. A drop in pressure after applying the nitrogen surely means there is a leak in the system which needs to be found and repaired.

Oxidation is an Enemy in Refrigeration – HVACR Pipe Soldering Brazing

Oxidation is an enemy of refrigeration systems and piping. Oxidation causes many problems with refrigeration systems and piping. To prevent oxidation when brazing refrigeration piping does not forget the slight amount of nitrogen in the system while brazing. It is important to only allow a slight amount of nitrogen into the system. Too much nitrogen pressure and the nitrogen pressure will not allow a good seal of the solder inside the pipe joint but push it out creating a tiny hole.

Conclusion | HVACR Pipe Soldering Brazing

Lastly, don’t forget to protect the piping when finished brazing or soldering. Proper piping support and protection from others tripping or running over the pipe is necessary. I was once on a construction project for a data center telecom building. The piping crew came in and installed the piping in a few days and left. The next day the painters came in and were using a lift and ran over some of the newly installed piping for a computer room air conditioner with the lift.

Furthermore, if you keep the system clean and follow good practices you will likely not have mechanical issues that will fall under warranty work. This warranty work typically costs your employer money which means less money for pay increases and benefits later on down the road. I see it all too often on job sites where someone takes a shortcut and then within six months that company has to return to replace a compressor or fix some other problem that could have been avoided if proper installation practices were used when installing the piping.

Following the basic guidelines, you can be successful at brazing and soldering. It does take some practice however following the basics as outlined here you can pick it up pretty quickly with a little practice. Good luck and here is another article to help you learn the basics of piping installation.

HVACR Pipe Soldering Brazing - Refrigeration Systems

HVACR Pipe Soldering Brazing - Refrigeration Systems

Technical Resource: Refrigeration and Air Conditioning Technology