How to Adapt Steel to Copper Water Pipes

Written by steve sloane
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How to Adapt Steel to Copper Water Pipes
Solder is used to seal the union to the copper pipe (reel of core solder image by Alex from

The joining of steel to copper water pipes requires the installation of a joint called a dielectric union. This union connects to the steel pipe by threading it into place and tightening it. The other end of the union is copper. The two ends of the union thread together and have a rubber gasket in between. The copper end of the union is soldered to a copper pipe. This copper pipe can then be connected via copper couplings and more pipe to various water fixtures (toilet, sinks, shower, etc).

Skill level:

Things you need

  • Hacksaw
  • Pipe wrench
  • Wire brush
  • Teflon tape
  • Union
  • Emery cloth
  • New copper pipe
  • Soldering paste
  • Propane torch
  • Roll of solder
  • Rag

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  1. 1

    Turn the water off at the main shut-off valve.

  2. 2

    Cut through the steel pipe with a hacksaw, then remove all unwanted steel pipe. Unthread and remove the remaining cut pipe from the nearest joint (coupling) with a pipe wrench. Then remove the coupling, also with the pipe wrench. This will leave the steel pipe with a bare thread on its end.

  3. 3

    Clean the thread with a wire brush. Wrap the thread clockwise with Teflon tape. Unthread the two halves of the union from each other and put the copper end and rubber gasket to one side. Thread the steel half of the union onto the pipe thread and tighten with a wrench.

  4. 4

    Screw the copper end of the union to the steel end (leave out the rubber gasket). Sand inside the copper end with emery cloth. Also sand the end of a piece of new copper pipe.

  5. 5

    Apply flux (soldering paste) to both the pipe end and inside end of the union. Push the pipe into the end of the copper union. Turn on the propane torch and uncoil 8 inches of solder from its spool.

  6. 6

    Heat the union/pipe area with the torch (both sides). When the flux sizzles, touch the tip of the solder to the seam between the union and pipe. If it melts, apply 3/4-inch of solder around the seam. Wipe away excess solder with a rag--it will be hot, so be careful.

  7. 7

    Unscrew the two halves of the union, once the copper joint has cooled. Place the rubber gasket between the two halves, then screw the two halves together. Tighten the two halves with the pipe wrench. The copper pipe that is soldered in place can now have other pipe and couplings attached, to reach the desired water fixtures.

Tips and warnings

  • Don't turn the water back on until all copper pipe has been soldered into place.
  • Always have a water spray bottle at hand when soldering.

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