You connect metal pipe to copper using a specific fitting designed to prevent corrosion.
Connecting Metal and Copper Pipes
When joining dissimilar metals like steel and copper, it's crucial to prevent galvanic corrosion. This occurs when two different metals are in contact with each other in the presence of an electrolyte, such as water, leading to the faster deterioration of the less noble metal (steel, in this case). Here’s how to do it properly:
The Dielectric Union
The recommended solution is using a dielectric union. This specialized fitting incorporates the following:
- Threaded Steel Female Pipe Fitting: This end connects to the male threads of the metal (e.g., galvanized steel) pipe.
- Female Copper Hub Fitting: This end is designed to slide over copper tubing.
- Dielectric Insulation: Most importantly, a dielectric material within the fitting isolates the two metals, preventing direct contact and, therefore, galvanic corrosion.
Steps to connect metal to copper pipe:
- Prepare the metal pipe: Ensure the threads are clean and free of damage. Apply thread sealant (such as PTFE tape) for a watertight connection.
- Attach the dielectric union (steel side): Screw the threaded steel end of the dielectric union onto the metal pipe. Tighten appropriately with a wrench.
- Prepare the copper pipe: Clean the end of the copper pipe.
- Attach the dielectric union (copper side): Slide the copper hub end of the dielectric union onto the copper pipe.
- Solder or press the copper side: Depending on the type of copper fitting on the dielectric union, either solder the connection using a torch and solder or press the connection using a press tool.
Why use a dielectric union?
- Prevents Corrosion: By physically separating the two dissimilar metals, it eliminates the conditions needed for galvanic corrosion.
- Ensures Longevity: The use of a dielectric union protects both the steel and copper components of your plumbing system.
- Industry Standard: It is the generally accepted and recommended method for connecting metal and copper pipes, ensuring safety and adherence to building codes.
Alternatives to Dielectric Unions
While the dielectric union is the most common, there are situations where it's necessary to use a different approach. Here's a brief comparison:
| Method | Description | Best use case | Advantages | Disadvantages |
|---|---|---|---|---|
| Dielectric Union | Separates metals with an insulator, female threaded steel and female copper ends. | Most common and recommended for standard connection | Effective at preventing corrosion | Can be bulkier, requires correct installation |
| Using a dielectric fitting combination | Combining a dielectric nipple (steel threaded to copper sweat) and separate fittings | Alternative in some limited situations | Flexibility in configuration | Requires more components and fittings |
By using a dielectric union, you ensure that you can connect metal pipe to copper safely and avoid issues with corrosion.
