Connecting copper pipe to galvanized pipe is possible, but it requires using the proper transition fittings and taking some precautions. There are a few key factors to consider when joining these two different pipe materials together in a plumbing system.
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The Differences Between Copper and Galvanized Pipe
Copper and galvanized pipe have very different properties that affect how they can be used together:
- Copper pipe is made from copper metal that is soft and malleable. It is joined by soldering copper fittings onto the ends of pipes.
- Galvanized pipe is made from steel that is coated with a thin layer of zinc to prevent corrosion. Galvanized pipe is threaded on the ends so that galvanized fittings can be screwed on.
- Due to their different materials and joining methods, copper and galvanized pipes cannot be directly connected to each other.
The key compatibility issue between copper and galvanized pipe is the difference in their expansion rates. Copper pipe expands and contracts more than galvanized with changes in temperature. This means if they are improperly joined, thermal expansion stresses can cause the joint to fail or leak.
Using Dielectric Fittings
To join copper and galvanized pipe, you need to use dielectric fittings. Dielectric fittings provide an insulating barrier between the two metals to prevent accelerated galvanic corrosion. Galvanic corrosion occurs when two dissimilar metals are in contact in the presence of an electrolyte – in plumbing systems this electrolyte is water.
The three main types of dielectric fittings used to join copper and galvanized pipe are:
- Dielectric Unions – Have a non-conductive plastic barrier between the threaded copper and galvanized ends. Allows easy disconnection later for maintenance.
- Dielectric Couplings – Have a non-conductive plastic sleeve lining the female threaded ends. Can be used to join pipes in a straight line.
- Dielectric Nipples – Short section of non-conductive plastic pipe with male threaded ends. Joins the two pipe materials in a small section.
The key is to make sure any dielectric fitting is designed and certified for use with potable water systems. Plastic materials like PEX or PVC are common insulators in these dielectric fittings.
Transition Joint Location
Where you place the dielectric joint when transitioning from copper to galvanized pipe is important:
- The joint should be installed as close as possible to where the pipe materials change.
- Long runs of copper and galvanized pipe on either side of the fitting should be avoided.
- Installing the dielectric union or coupling within 1-2 feet of the material transition is ideal.
This placement limits the length of dissimilar metal contact and minimizes the potential for galvanic corrosion in the system.
Check for Proper Installation
When installing a dielectric fitting between copper and galvanized pipe, be sure to:
- Only use fittings listed for dielectric isolation with potable water.
- Clean and sand joining surfaces to improve contact and prevent leaks.
- Make sure pipe ends are square and fittings align properly.
- Pay attention to flow direction arrows on dielectric nipples and couplings.
- Tighten fitting joints securely, but do not overtighten.
Proper installation ensures the joint will be sealed and the dielectric barrier will function as intended.
Consider Replacements
In some cases, replacing galvanized pipe with copper may be a better long-term option. Factors that support replacement include:
- The galvanized pipe is old with buildup and corrosion.
- The system requires many joints between the materials.
- You need to increase the water flow capacity.
Replacing galvanized with copper avoids dielectric fittings and gives a more compatible system. Consult with a licensed plumber on the best option.
Conclusion
Joining copper and galvanized pipes should only be done with proper dielectric fittings that isolate the two metals. This prevents accelerated corrosion. The joint location should be as close to the material transition point as possible. With the right fittings installed correctly, copper and galvanized pipe can be joined successfully. But in some cases, full galvanized replacement provides the best reliability in the long run.