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Soldering Copper Tube

The basics with the right instructions and background make many home repairs quite simple, and that goes for soldering copper tube, too. Soldered joints are the most reliable for your plumbing, and it’s not as difficult to do as you might think. The following instructions and techniques produce leak-free soldered joints between copper and copper alloy tube and fittings. The Pipe, Tube and Fittings Copper Development Association recommends reading through the instructions carefully, taking all possible safety precautions and doing a trial run. The following detailed steps may seem imposing, but after doing a trial run they should become clear and quite simple. Use only lead-free solder identified for potable water applications, meeting ASTM B 32. Use fluxes intended for use with lead-free solders, meeting ASTM B 813. Avoid using ‘self-cleaning’ fluxes. Your local hardware store can advise you if you are unsure.

1. Measuring Measure and mark the tube with a pencil. Remember to allow for the length of tube that fits into the fitting cup. Dry-fitting the tube and fittings before soldering will ensure that the fittings are square and the runs straight.

2. Cutting Cut the tube to the measured length. The tube can be cut with a disc-type tube cutter, a hacksaw, an abrasive wheel, or with a stationary or portable band saw. Care must be taken that the tube is not deformed while being cut. Regardless of the method, the cut must be square to the run of the tube so that the tube will seat properly in the fitting cup.

3. Reaming Ream all cut tube ends to the full inside diameter of the tube to remove the small burrs created by cutting. If the rough, inside edge is not removed by reaming, erosion or corrosion may occur due to local turbulence and increased local flow velocity in the tube; a properly reamed piece of tube provides a smooth surface for better water flow. Also remove any burrs on the outside of the tube end created by the cutting to ensure proper entrance of the tube into the fitting cup. Tools that can be used to ream the tube end include the reaming blade on the tube cutter, half-round or round files, a pocketknife or a suitable deburring tool. If you are using soft tube (annealed) you must be very careful to not deform the tube end by applying too much pressure.

4. Cleaning The removal of all oxides and surface oil from the tube end and fitting cup is crucial to allow the proper flow of solder metal into the joint. Failure to remove them can interfere with capillary action and may lessen the strength of the joint. Lightly clean the tube end using sand cloth or nylon abrasive pads for a distance slightly more than the depth of the fitting cup. Clean the fitting cup by using abrasive cloth, abrasive pads or a proper-sized fitting brush. The capillary space between tube and fitting is approximately 0.004″. Solder metal fills this gap by capillary action. This spacing is critical for the solder metal to flow into the gap and form a strong joint. Copper is a relatively soft metal. If too much material is removed from the tube end or fitting cup, a loose fit may result in a poor joint.

5. Applying Flux Use a flux that will dissolve and remove traces of oxide (which is usually blackish in color) from the cleaned surfaces, protect the cleaned surfaces from reoxidation during heating, and promote wetting of the surfaces by the solder metal. It is also important to use fluxes that meet the ASTM B 813 standard so that any flux residue left inside the system will flush out with water. Apply a thin, even coat of flux with a brush to both the tube and fitting as soon as possible after cleaning. WARNING: Do not apply the flux with your fingers. Chemicals in the flux can be harmful if they come into contact with the eyes, mouth or open cuts. Careless workmanship can cause problems long after the system has been installed. If excessive amounts of flux are used, the flux residue can cause corrosion. In extreme cases, such flux corrosion could perforate the wall of the tube, the fitting or both.

6. Assembly and Support Insert the tube end into the fitting cup, making sure the tube is seated against the base of the fitting cup. A slight twisting motion ensures even coverage by the flux. Remove excess flux from the exterior of the joint with a cotton rag. Support the tube and fitting assembly to ensure a uniform capillary space around the entire circumference of the joint. Uniformity of capillary space will ensure good capillary flow of the molten-solder metal. Excessive joint clearance can lead to solder metal cracking under conditions of stress or vibration. The joint is now ready for soldering. Joints prepared and ready for soldering must be completed the same day and should not be left unfinished overnight.

7. Heating Begin heating with the flame perpendicular to the tube. The copper tube conducts the initial heat into the fitting cup for even distribution of heat in the joint area. The extent of this preheating depends on the size of the joint. Preheating of the assembly should include the entire circumference of the tube in order to bring it up to a suitable temperature. However, for joints in the horizontal position, avoid directly preheating the top of the joint to avoid burning the soldering flux. Practice and experience will indicate the amount of heat and time needed. Next, move the flame onto the fitting cup. Sweep the flame alternately between the fitting cup and the tube a distance equal to the depth of the fitting cup. Again, preheating the circumference as described above, with the torch at the base of the fitting cup. Touch the solder to the joint. If the solder does not melt, remove it and continue heating. Do not overheat the joint or direct the flame into the face of the fitting cup. Overheating could burn the flux, which will 7. Heating (continued) destroy its effectiveness, and the solder will not properly enter the joint. When the solder melts, apply heat to the base of the cup to aid capillary action in drawing the molten solder into the cup toward the heat source. The heat is generally applied using an air-fuel torch. Such torches use acetylene or an LP gas. Electric resistance soldering tools can also be used. They employ heating electrodes and should be considered when an open flame is a concern.

8. Reaming Ream all cut tube ends to the full inside diameter of the tube to remove the small burrs created by cutting. If the rough, inside edge is not removed by reaming, erosion or corrosion may occur due to local turbulence and increased local flow velocity in the tube; a properly reamed piece of tube provides a smooth surface for better water flow. Also remove any burrs on the outside of the tube end created by the cutting to ensure proper entrance of the tube into the fitting cup. Tools that can be used to ream the tube end include the reaming blade on the tube cutter, half-round or round files, a pocketknife or a suitable deburring tool. If you are using soft tube (annealed) you must be very careful to not deform the tube end by applying too much pressure.

9. Cooling and Cleaning Allow the completed joint to cool naturally. Shock cooling with water may stress the joint. When the joint is cool, clean off any remaining flux residue with a wet rag.

10. Congratulations Now, stand back and admire your work ‹ it will last a lifetime.

More information on copper applications and installation can be found at www.copper.org

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