How to Join Dissimilar Metal Pipes

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Joining dissimilar metal pipes can cause problems at the joints if the proper precautions are not taken. The metals commonly used for pipes, copper and steel, have a small microvolt electrical potential. When joined directly, the differences in the electric potential of dissimilar metal pipes causes a small current to be produced. This current, when acted upon by water, turns the pipe joint into a small battery. This creates a buildup of corrosion, which soon causes a failure at the pipe joint. You can prevent these effects by using a special dielectric union device. The device electrically separates the two types of pipe. Installation of the device is simple, and will save you in both repair and replacement costs.

Things You'll Need

  • Dielectric union
  • Propane torch
  • Solder
  • Adjustable wrench
  • Turn off any water leading to the pipes.

  • Separate the dielectric union into its component parts. The dielectric union is a joining piece that has different couplings that attach to the ends of dissimilar pipes and a large nut that joins the couplings together. For example, for joining a copper pipe and a steel pipe, you should have a nut that clamps the separate pipes together, a brass coupling, a steel coupling, washer and insulator.

  • Thread the steel coupling onto the steel pipe using the pipe wrench. Place the steel coupling so that it slides over the end of the pipe with the larger end of the coupling flaring from the end of the pipe.

  • Slide the steel nut onto the copper pipe so that it can slip onto the brass coupling.

  • Place the brass coupling onto the copper pipe. Place the coupling so that the smaller end is against the end of the pipe. The larger end that joins the steel coupling should flare outward from the pipe end to serve as the joint.

  • Solder the joint closed to prevent leaks. Light and adjust the propane torch until the blue section of the flame is two inches long. Place the tip of the blue flame against the fitting where the pipe and coupling join. Heat the joint for about five seconds, and then remove the flame. Place the solder on the opposite side of where the flame was placed. Allow it to melt and flow onto and fill the joint. Run the solder once around the seam to make certain all areas are covered. Allow the joint to cool completely.

  • Place the plastic insulator onto the brass coupling. The insulator keeps the dissimilar pipes from touching, which interrupts the electric current, preventing the battery effect that causes the corrosion.

  • Place the two ends of the coupling together with the washer between to help create a watertight bond. Push the steel nut over the brass coupling onto the threading on the steel coupling. Tighten the nut using the pipe wrench.

  • Start the water supply and test the connection for leakage. If leakage occurs, tighten the nut or resolder the brass coupling as needed.

Tips & Warnings

  • Dielectric unions can be used to fit other dissimilar pipe types, Purchase one that is made specifically for the two pipe types being joined.
  • Protective work gloves and goggles should be worn throughout the installation process.
  • Keep a fire extinguisher close when using the propane torch.

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References

  • Photo Credit few rusty nails image by Sergey Minaev from Fotolia.com
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