How to Weld Copper Plumbing

Welding copper together requires a torch and solder.

Welding two copper pieces of plumbing together is a basic plumbing skill that you can apply to a wide variety of home-improvement projects. Unlike traditional metal welding, copper pipes are held together using solder as an adhesive between the metal pieces. This process is known as "sweating" the pipe. Welding copper plumbing is one of the most secure ways of creating a watertight connection between pieces that will last for decades without maintenance.

Things You'll Need

• Copper pipe fittings
• Fine-grit sandpaper or copper brush
• Rag
• Flux and flux brush
• Heat torch
• Solder

Instructions

1. Swab the inside of both pieces of copper that are to be fitted together using a copper brush or fine-grit sandpaper until the connections are shiny. Use a fine-grit sandpaper to polish the outside of the straight pipe at least 2 inches in from the end of the pipe. Wipe all of the polished surfaces with a rag to provide a clean welding surface.

2. Assemble the copper pieces to make sure they fit. Disassemble the pieces when you are confident they fit together properly.

3. Apply a thin layer of copper flux to all of the metal surfaces that will touch when welded. This includes the inside of fittings and the outside of pipes. Press the pieces together.

4. Slowly move an open flame from a torch around the area of a fitting where the straight pipe attached. Heat for at least 10 seconds.

5. Press a piece of solder to the highest point on the outside seam where the two pieces meet. The heat will draw solder into the fitting. Keep holding the solder to the seam until solder begins to drip from the bottom of the connection. When solder appears at the base, the joint is filled with solder.

Tips & Warnings

• Pipes that are heated with a torch will remain hot for up to 30 minutes, so use extreme caution when handling heater copper.

References

• Easy2DIY: Soldering Copper Pipes
• This Old House: How to Solder Copper Pipes