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Join Copper and Galvanized Steel Pipe

Use dielectric unions to stop corrosion

FH05DJA_JOINCO_02-3 galvanized steel pipeFamily Handyman
Water leaks from old galvanized steel water pipe are common at joints, especially when they're joined to copper. Use a dielectric coupling when fixing the problem to prevent further damage.

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Replace a leaky galvanized steel pipe

Dielectric union

Dielectric unions stop corrosion between different types of metal by using a rubber or plastic washer and sleeve to keep the metals from touching.

Joining copper and steel

Solder the brass half to the copper pipe, thread the steel half onto the galvanized steel pipe with Teflon tape, then join the two together tightly with the joining nut.

It’s far easier to make a repair to steel pipe with copper than with galvanized plumbing pipe, because the galvanized calls for cutting threads on exact lengths of pipe. But first, call your local plumbing inspector or water utility and ask for a pipe recommendation. The water in some regions is highly corrosive to copper, making plastic (CPVC or PEX) a better choice.

Also be aware that directly joining two different types of metals, in this case, galvanized steel pipe and copper, can cause rapid corrosion at the joint (called dielectric corrosion). To limit this problem, make the steel/copper connections with special dielectric unions rather than with a regular coupling. This type of union separates the two metals with a rubber washer and plastic sleeve so they don’t actually touch each other.

To remove the old leaky joint, turn off the water at the main entry, drain the system and cut the pipe near the joint with a hacksaw. With a pipe wrench, remove the pipe back to the nearest joints, working in both directions. Check the joints to see if they’re clogged or badly corroded as well. If so, consider continuing back until you find a clean, solid fitting. Unfortunately, one bad joint often means others or much of the system needs replacing too. Add a new galvanized steel pipe length (nipple) at each end and solder in your copper. (Use sandpaper as needed for cleaning pipe.) Then take the union apart and solder the brass end to the copper and screw the steel end to the galvanized pipe. Finally, join the two ends with the large nut.

Required Tools for this Project

Have the necessary tools for this DIY project lined up before you start—you’ll save time and frustration.

  • Adjustable wrench
  • Hacksaw
  • Pipe wrench
  • Plumbers tape
  • Soldering torch
  • Tube cutter

Required Materials for this Project

Avoid last-minute shopping trips by having all your materials ready ahead of time. Here’s a list.

  • Copper pipe
  • Dielectric union
  • Flux
  • Sandpaper
  • Solder
  • Steel nipple