How to Fix Galvanic Corrosion

Galvanic Corrosion is an electro/chemical process in which one metal corrodes preferentially to another when both metals are in electrical contact, in the presence of an electrolyte. wikipedia.com

In plumbing the process takes place when pipes, made of different metals, are joined together. Most often this is copper and galvanized steel water pipe. Water in the system, along with minerals and various chemicals contained in drinking water, provides the electrolyte bath. The most common occurrence is at water heaters where copper water pipe connects to the steel tank of the heater.

As you can see in the photo, the iron nail is being corroded by the copper wire. In galvanic corrosion the greater the difference of electro-potentials of the metals the faster corrosion takes place. In the case of copper and galvanized steel the difference is quite large, even greater than the iron nail shown. In situations where copper pipes are directly connected to steel pipes the steel corrodes quickly.

If we have a water heater, which has a steel tank with two threaded steel outlets, and copper adapters are screwed directly into those outlets, it is only a matter of time before the steel corrodes and the tank begins to leak. When the tank begins to leak there is no choice but to replace the heater.

So why does anyone connect copper pipes to a steel water heater tank, and how can we make a connection that will not cause corrosion?

People make direct connections because they don't understand galvanic corrosion and/or they don't know the proper way to connect dissimilar types of pipe. The goal is simply to keep the dissimilar metals away from each other. Teflon tape or pipe joint compound on the threads will not accomplish this! We need better isolation. In the picture below you can see that the copper adapters which were connected directly to the water heater tank have been removed and replaced by isolating nipples.

The nipples used in the tank are “dielectric nipples” made of a non-conductive allow and lined with plastic. This breaks the electrical bond between the dissimilar metals and also with the water (electrolyte) inside the pipe. From there I used a heavy brass push-on fitting to eliminate the need of soldering.

We could also use a dielectric union. They use a rubber gasket between the union faces and a plastic collar between the union nut and the copper part of the union to isolate the dissimilar metals from contact. The goal again is to keep the dissimilar metals and the electrolyte bath provided by the water inside the pipe from making contact.

We have looked at water heaters, but anywhere copper meets steel is a potential for corrosion. In older homes and buildings galvanized water mains are often replaced or repaired using copper tubing without proper isolation. This only causes already corroded pipes to corrode faster. Anywhere copper or brass meets steel dielectric nipples and/or fittings should be used for the transition.

As you can see in the picture above it is not a difficult nor expensive procedure to properly isolate your steel water heater tank from the copper water lines attached to it, and it could prevent the very costly need to replace a corroded and leaking water heater. Dielectric nipples are available in pairs for under $10 (USD) and push-on fittings are around $6 (USD) each, so for less than twenty-five bucks you can save yourself from having a corroded water heater. That replacement could run over a grand!