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How To Solder Copper Pipes Return to Heating University Main Page

Caution: Please read and understand all safety information before attempting maintenance or repairs. Wear eye protection and gloves when soldering pipes and when working with flux. Flux is a toxic substance. Some equipment may rely on a cold water supply. Take appropriate steps to shut down any equipment that may be adversely affected by shutting off the water supply. Such equipment includes, but is not limited to, a boiler or other heating system. Note: Because you are working with a flame, often in a confined space, be aware of flammable materials near where you are working. In some cases, you may need to set up a non-flammable heat shield between the solder joint and flammable material nearby. Check with your local authority for applicable codes about the work you wish to perform and the necessity of permits before you begin your project.
When copper pipes are fitted together, there is a very small gap between the two pieces. When the pipes are heated, and solder is touched to the pipes, the solder melts and is drawn up into the gap through capillary action. Once the gap is filled, and the heat removed, the solder forms a seal and makes a watertight joint. Soldering pipes is easy once you get the hang of it. The key is to recognize that you are heating the pipes, not the solder. The heated copper melts the solder. Follow the steps in this guide and you should be able to make watertight joints. It is recommended that you practice a few times on some spare parts until you feel confident.
click image for larger picture	Remove all burrs from the inside and outside edges of the pipe with a deburring tool. Small burrs can result in a variety of problems in the lifespan of the water supply system.
click image for larger picture	Clean the outside of the copper pipe to a brilliant shine with a copper pipe cleaning brush, or simply use steel wool or emery cloth. If the copper is not clean, the solder may not bond properly and the joint may leak.
click image for larger picture	Clean the inside of the female fitting in the same way as in step 1.
click image for larger picture	Apply acid-free flux to both the outside of the male fitting and the inside of the female fitting. Flux further cleans the copper plus helps to prevent oxidation as the pipe heats up. If the pipe becomes oxidized, the joint may leak.
click image for larger picture	Join the two pieces securely together. Unroll about four inches of solder and straighten it. You will use the roll or container as a handle when applying the solder. Light the torch and apply the flame to the joint. Move the flame around to ensure that you heat the pipe on the opposite side from you.
click image for larger picture	When the flux begins to bubble and spit, touch the tip of the solder to the joint. The solder should melt immediately and disappear into the joint. Remove the heat. Work quickly because the pipe's temperature will drop quickly. Move the tip of the solder around the entire joint to ensure that solder fills in all the way around. If the joint stopped taking up solder because the solder was not melting, then quickly add more heat so that more solder can be applied. Once the joint will take no more solder it will build up outside of the joint and begin to drip. Care should be taken at this point. Disrupting a joint as it cools can result in a dry joint also known as a leak. Once the joint has hardened, it can be wiped. This is the part where experience/practice helps. Some people use a dry rag, so the joint can be cleaned, but not cooled to the point, where it creates a dry/leaky joint.
Notes: Always check for leaks after the pipe has cooled. If you overheat the copper, it will oxidize and that prevents the solder from bonding. If the joint leaks, you must open the joint, remove all the solder and start over by cleaning the metal and applying flux. It may be easier to start over with new fittings. Always use lead-free solder. Make sure the pipes are completely dry or it will interfere with the bonding of the solder. If you cannot completely stop the flow of water from the pipe you are working on, it may be impossible to heat the pipe hot enough. Take a wad of white bread (without the crust) and stuff it into the pipe. This will hold the water back for a minute or two. After that the bread will dissolve harmlessly in the pipe and is easily flushed out. Specialty parts may have requirements to disassemble seals or other components. Please read all instructions from each manufacturer. When sweating ball valves, it is best to point the flame away from the piece, sweating the ball valve as quick as possible. If you use MAPP gas instead of propane, it burns much hotter and will heat the copper very quickly compared to propane. If you are used to propane, practice with MAPP before beginning work.

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