Galvanic Corrosion

Today’s topic is a not so uncommon plumbing problem. While remodeling in Boise, we at Levco see all sorts of things. This problem was discovered in the utility room. The effects were carried throughout the daylight basement ceiling.

Usually, what people are really referring to when they say electrolysis is galvanic or dissimilar metal corrosion. Galvanic corrosion is caused by self-induced current created by the electrical potential of two dissimilar metals in contact with an electrolyte. The more noble metal attacks the less noble. This occurred on a recent project when two dissimilar metals, copper tube and galvanized steel pipe, were connected in the presence of an electrolyte solution also known as water.

Typically, a homeowner will go pick up some plumbing parts to fix a problem. Hey, if the threads fit together that must mean they were meant to screw together. Turns out it is a little more complicated than that. Connecting dissimilar metals, which is commonly done by accident in residential plumbing, can start a chain reaction leading to pipe failure and leaks in the less noble metal. (the galvanized pipe in this case)

One form of proper connection is called a dielectric connection. They can be purchased at most hardware stores. It keeps the metals separated by a rubber piece. Another fix is to use a brass bushing between the galvanized pipe and the copper pipe.

The smoking gun we found had a direct copper to galvanized pipe connection, a recipe for disaster. We also found copper to bronze to galvanized which is OK. When we took the ceiling down, we found a ticking time bomb (so to speak) with multiple pin holes in the galvanized pipe, which we would expect from the bad connection.

Fixing the problem involved ripping out the down stream pipes and replacing them. In addition to the outward signs of corrosion, we also found what looked like massive mineral build up in the pipes which reduced its water carrying capacity.

Water heaters are a common place for this corrosion to occur, so they all have a sacrificial anode in them that will dissolve instead of eating a hole in the tank.

Although these principles seem obvious, they are the cause of countless headaches and occasional pipe failures. It may not be the manly thing to do to ask for plumbing advice, but make sure that when you do, it comes from a trusted, knowledgeable source.

Your comments are welcome. To ask questions or get more information about remodeling, email me directly or visit our contact page.

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