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Join Copper to Galvanized Pipe

How To Connect Copper Pipe to Galvanized Pipe

Any home is eventually going to require replumbing of water supply pipes. Copper pipe has long been an excellent choice because of its resistance to corrosion. Copper is also easy to install and there may be benefits from its natural anti-microbial properties as well.

Many homes are plumbed with galvanized steel pipe because it was the standard from the 1940's through the 1970's. The problem with galvanized pipe is that it reacts with the minerals in the water supply. The reaction creates scale, which will eventually clog the pipe.

Eventually galvanized pipe will have to be replaced, and when that happens, your choices are to replace it with more galvanized pipe, copper pipe or plastic pipe. Replacing with galvanized pipe might seem like the easiest choice but that might not be true. First, the new galvanized pipe is destined to fail, although you may not be concerned about what will happen thirty or so years from now. Secondly, installing galvanized pipe into a fixed location, of a exact size and connecting it to other galvanized pipe which may be close to failure, may be more difficult than you think.

Because copper pipe is easy to work with and cut to length, it may be your best option as a replacement for a section of galvanized pipe. But you may be wondering, "how do I connect a piece of unthreaded copper to threaded steel pipe?" And the answer is, with a dielectric union. The union has threads on one side for the steel pipe and a female slip joint for a solder connection to copper pipe. The "dielectric" part is the metal transition feature that prevents electrolytic corrosion from occurring as a result of the joining of copper and galvanized steel. If the union was not a dielectric one, the metals would quickly corrode and fail.

To install a dielectric union, take apart the dielectric union. Clean the threads of the galvanized pipe and apply pipe joint compound (aka pipe dope) or PTFE tape to them. Install the threaded part of the union onto the threaded pipe and tighten securely.

Clean the end of the copper pipe, about one inch, thoroughly with emery cloth until shiny. Slip the large union ring over the copper pipe, then slide the plastic sleeve onto the pipe. Apply soldering flux to the end of the pipe, about 3/4 inch, and then finally slide on the slip joint side of the union. Sweat (solder) the fitting onto the copper pipe. Cool the pipe by misting it with water and handle it with a wet rag. Align the two pipe fittings and thread the large union ring. Tighten the ring securely, turn on the water and inspect for leaks.

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