What fitting is used to join copper with galvanized pipe?

When joining copper and galvanized steel pipes in a plumbing system, the correct fitting must be used to create a solid, leak-free connection. The most common method is to use a dielectric fitting, which separates the copper and galvanized components while allowing them to be threaded together. Dielectric fittings prevent galvanic corrosion, which occurs when two dissimilar metals come into contact in the presence of an electrolyte like water. The electrochemical reaction causes accelerated corrosion and erosion of the pipe material. Using the proper fitting keeps the system safe and functional over the long term.

Reasons for Joining Copper and Galvanized Pipes

There are several scenarios in which copper and galvanized steel pipes need to be connected in a residential or commercial plumbing system:

– Transitioning from underground galvanized pipe to copper pipes in the building. Underground pipe is often galvanized steel because it is cheaper and better able to withstand impact from digging and ground movement. Above ground pipes are usually copper which has better flow and is easier to work with for fixtures and joints. A dielectric fitting allows the transition from one material to the other.

– When galvanized pipe is already in place. In older construction, galvanized steel pipe may have been used throughout the plumbing system. When making repairs or extensions, new copper pipes can be integrated using dielectric fittings. This avoids having to replace all the galvanized pipe.

– Connecting galvanized components. Some components in plumbing systems such as nipples, unions, and valves may be made of galvanized steel. Dielectric fittings allow connection of these galvanized components to copper pipe runs.

– Transitioning between piping materials. Dielectric fittings can also be used when transitioning between galvanized pipe and other materials such as PVC plastic pipes. The same galvanic corrosion issues arise so dielectric isolation is needed.

Problems with Joining Dissimilar Metals

Galvanic corrosion occurs when two different metals are in contact in the presence of an electrolytic solution like water. One metal acts as the anode and corrodes faster than normal while the other acts as the cathode and corrodes slower. This leads to premature failure at the joint.

In the case of copper and galvanized steel pipe, the copper is the anode while the galvanized steel is the cathode. The copper corrodes rapidly, causing pitting and erosion. Eventually, this can lead to pinhole leaks and total failure at the joint.

Some key factors influence the degree of galvanic corrosion:

– Differences in nobility. The further apart the two metals are in the galvanic series, the more severe the corrosion. Copper and galvanized steel are quite far apart, making this a high-risk pairing.

– Ratio of anode to cathode surface area. More corrosion occurs when the anode area is much smaller than the cathode area. This is often the case when joining a short section of copper pipe to a galvanized system.

– Electrical resistance of the water. Pure water has low conductivity. However, dissolved salts and minerals increase conductivity, allowing more current flow and corrosion. Hot water accelerates the process as conductivity increases with temperature.

Dielectric Fittings for Joining Copper and Galvanized Pipe

Dielectric fittings contain an insulating material that separates the copper and galvanized components to prevent metal-to-metal contact and galvanic corrosion. There are two main types of dielectric fittings used:

Dielectric Unions

These fittings allow easy connection and disconnection of copper to galvanized pipe runs for maintenance and repairs. They have a separate copper end and galvanized end joined by a dielectric insulator such as plastic. The key components are:

– End connectors. One end has a standard copper fitting while the other has a galvanized steel fitting. Common types are solder copper joint and female threaded steel joint.

– Center section. A non-conductive nylon or plastic separator between the metal ends. This completely isolates the copper and galvanized sections.

– O-ring seals. Rubber O-ring seals prevent water leaking across the insulator barrier. Quality fittings should have O-rings on both sides.

Dielectric unions have good mechanical strength but are bulky and expensive. They are best used in accessible locations to allow for system maintenance.

Dielectric Couplings

These fittings don’t allow disconnection but provide an inexpensive permanent joint. Key features include:

– Threaded ends. The fitting has male tapered thread fittings on both ends – typically NPT or BSP standard.

– Plastic or resin insulator. A plastic sleeve isolates the threaded ends from each other. Quality couplings have a full 360?? non-conductive barrier.

– Good mechanical strength. The plastic sleeve is bonded into the threaded ends so the whole unit can withstand high pressures. A wire mesh reinforcement improves strength.

Dielectric couplings are the most economical option for most copper to galvanized joints and ideal for inaccessible locations like underground.

How to Install a Dielectric Fitting

Installing a dielectric fitting between copper and galvanized pipe is straightforward:

1. Cut pipe ends square – Cut back both pipes so you have a straight end without dents or damage. Deburr the pipe ends.

2. Clean and prepare joint areas – Clean the outside of the pipe to remove dirt, grease and corrosive fluxes. Prepare the mating joint areas according to the fitting instructions.

3. Apply joint compound or tape – For threaded dielectric fittings, apply joint compound or PTFE tape to the threads. For solder joints, apply flux to the mating surfaces.

4. Join copper pipe end – Attach the copper pipe to one end of the dielectric fitting using the appropriate technique – soldering, brazing or threading. Follow standard joint guidelines.

5. Join galvanized pipe end – Attach the galvanized pipe to the other end of the fitting. Threaded joints only require hand tightening. Ensure threads are fully engaged.

6. Check for leaks – Test the joint under pressure and inspect for leaks. Check O-ring seals have created a watertight barrier between the galvanized and copper components.

Following manufacturer instructions for preparing, joining, and pressure testing will result in a galvanically isolated, leak-free connection between the pipes. Periodically check joints for any signs of water leaks or corrosion.

Dielectric Fittings Required by Code

Dielectric fittings for connecting copper and galvanized pipe are mandated by plumbing codes. Both the Uniform Plumbing Code and International Plumbing Code state:

> Ferrous and non-ferrous piping shall not be joined together without a proper dielectric fitting/connection.

Therefore, dielectric isolation is not optional – it is required whenever these two metals are joined to prevent dangerous galvanic corrosion. Other relevant codes include:

– IPC 422.4 – Dielectric Waterway Fittings
– UPC 609.3 – Separation of Materials
– UPC 609.10 – Dielectric Pipe Unions
– UPC 609.11 – Dielectric Couplings

Plumbing inspectors will check that proper dielectric fittings have been used. Failing to follow code requirements could mean rejection and rework of pipe joints.

Best Practices for Dielectric Fittings

To achieve good results with dielectric fittings:

– Use reputable, high-quality fittings – Cheap fittings often have substandard insulation barriers. Stick with established brands.

– Ensure full isolation – Fittings must have a complete non-conductive barrier between the copper and steel. Check visually.

– Limit galvanized connections – Minimize the number of joints between copper and galvanized to reduce corrosion risk.

– Favor unions over couplings – Unions allow inspection and maintenance. But couplings cost less.

– Check periodically – Visually inspect dielectric fittings to check the insulation barrier remains intact over years of service.

– Avoid untreated steel – Dielectric fittings do not work on bare steel – an insulating coating is required. Use galvanized or black steel pipe only.

– Prevent moisture contact – Insulation and sealing can help keep the insulation dry and conductive.

Following these best practices will maximize the service life of plumbing systems that integrate copper and galvanized pipe components.

Dielectric Fittings for Other Metal Combinations

While most commonly used between copper and galvanized steel, dielectric fittings can also be used to join:

Metal 1	Metal 2
Copper	Cast iron
Copper	Carbon steel
Stainless steel	Carbon steel
Copper	Stainless steel

The same galvanic corrosion issues arise when joining dissimilar metals. Using an appropriate dielectric fitting provides galvanic isolation and prevents premature corrosion and leaks.

Conclusion

Dielectric fittings containing plastic or resin insulation barriers are mandatory when joining copper and galvanized steel pipes. They prevent galvanic corrosion caused by contact between the dissimilar metals. Dielectric unions allow simple inspection and maintenance while dielectric couplings provide cheaper permanent joints. Following codes and best practices when installing dielectric fittings ensures safe, long-lasting plumbing systems. Periodic inspection is advised to check for corrosion and replace deteriorated fittings as required.