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How to Solder a Copper Pipe

Debopriya Bose Jun 18, 2019
Soldering is a method of joining two metal objects by heating them. In this process, the soldering material flows in to form a tight joint. This method is very useful in joining copper pipes.
Copper pipes are very useful in containing water, refrigerants, or air. Hence, they are commonly used in transporting these materials. However, for bending a copper pipe, one has to join it at an appropriate angle with a fitting. This can be done by soldering each end of a fitting, at the point where the pipes have to bend.

What is Soldering?

Soldering works by capillary action. When the pipe and the fitting are heated, the soldering material is touched to the joint. The heat melts the material, and by capillary action, it is sucked into the joint, sealing it.
Once the material cools, an air-tight joint is formed. Thus, sealing the copper pipes and the fitting tightly together. It is important that this material has a lower melting point than copper. Otherwise during the heating process, the metal pipes may melt.

The Procedure

Cutting the Pipe

Cut the pipe of required length. As copper is a soft metal, it can be cut neatly using a tube cutter. However, in case of larger pipes, a hacksaw may be used. If you are using a hacksaw, then ensure that the all the burrs at the end of the pipe are filed.

Cleaning the Pipe

Cleaning the pipe and fittings, and making them rust-free is an important step for sweating the pipe. Sandpaper, emery cloth, and steel wool would be good for cleaning the outer surface. However, to clean the inner surface of the pipe and the fitting, cleaning brushes would be more effective.
These brushes are available in various sizes. Brushes that suit the required sizes can easily be bought from the market. Apply a liberal coat of flux on the inner side of the fitting and on the outer side of the pipe. Place the fitting at the end of the pipe and move the pipe or the fitting back and forth so that the flux spreads evenly over the surfaces.
Fluxing the objects ensures that even the minutest trace of tarnish is removed. Moreover, it reacts slightly with the molten solder and removes impurities from it. This helps the solder to flow freely into the joint.


Put the pipe into the fitting. The heating equipment to be used depends upon the pipes' dimensions. If you are using small pipes, then using a propane torch would be enough. However, for larger ones, one should use a plumber's acetylene torch.
As copper is an excellent conductor of heat, heating the fitting at a single point or at a point close to the joint would work. Hold the flame for sometime, so that the temperature of the object that you are heating, reaches the melting point of the soldering material. Although 10 - 20 seconds would be enough, larger pipes may take a little longer.
Once you feel that the joint has achieved the right temperature, touch the soldering wire at the joint. If it melts, then it means that it has been heated to the correct temperature level. Keep testing it by touching the soldering wire to the joint.


Touch the wire to the joint once you are sure that it has attained the appropriate temperature. The solder will melt and be pulled into the joint between the pipe and the fitting through capillary action. In case the pipe is small, there is no need to move the wire all along the circumference of the joint.
As the solder melts, it will be drawn into the joint along its entire circumference. Once the molten solder starts pouring out, it indicates that the pipes no longer requires it to fix the joint. Be careful that, not too much of the material melts and accumulates inside the joint, because it will form bumps, that will hinder the water flow through the pipe.

Wiping the Joint

Once the pipe has cooled down a little, take an old rag, fold it a few times so that it is thick enough to protect your fingers from the hot metal. You could also moisten it a little. Now quickly wipe the excess solder and flux away from the joint to ensure that there are no blobs.
Nothing looks better than a bright clean shiny joint with a band of silver gray at the joint. In case you are using a wet rug, it may cool the pipe quickly, leading to the formation of blobs. If that is the case, reheat the joint to remelt, and wipe off the excess solder and flux.

Precautions to be Taken

  • Always wear safety glasses during the process.
  • Never solder directly overhead.
  • Wear a glove while applying the flux as it may damage the skin.
  • Use a heat shield if you have combustible substances close to the soldering area.
  • Keep a fire extinguisher close by.
Soldering is a simple process that can be carried out at home. Once you master this technique, you can tackle a number of domestic repair works.