Dielectric Unions

This article will be a bit more scientific than most on this blog, but it’s important, so don’t let that deter you from reading. If you aren’t a trained plumber or didn’t pay close attention in chemistry class, there’s a good chance you don’t know what a dielectric union is. It’s actually not as complicated as it sounds, though, and hopefully you’ll find it interesting.

Dielectric unions are required when joining dissimilar metals to prevent a reaction called galvanic corrosion. “Galvanic” refers to electrical currents created by a chemical reaction, and “corrosion” refers to the gradual destruction of a material – usually metal. So, in layman’s terms, galvanic corrosion on pipes is the gradual destruction of the metal as a result of a chemical reaction that causes electricity.

But how, exactly, does that work? When two dissimilar metals, like copper and steel, are joined together and water passes between them, the water acts as an electrolyte and causes ions from one metal to separate and move to the other. Basically, the metals and water form a battery, so to speak. If you’ve seen older batteries, you’ve likely noticed some corrosion. This doesn’t happen immediately, but it is guaranteed to happen over time if there’s nothing done to prevent it.

So what’s the remedy for this natural occurrence? You guessed it… a dielectric union. The union contains a rubber gasket in the middle that prevents the different types of metals from touching. Unlike metal, the rubber does not conduct electricity. As a result of this non-conductive separation, the harmful chemical reaction (electrolysis) is essentially prevented and the unwelcome corrosion is kept at bay.

Joining dissimilar metals is fairly common with plumbing work, but it’s especially common at water heater fittings. This is one reason why many water heaters show corrosion in different places, and it’s one of many reasons why qualified plumbers who know how to properly join pipes and fittings need to be the ones installing water heaters (and performing other more detailed plumbing jobs). The last thing you want is a malfunctioning and potentially dangerous water heater!

When you get some spare time, it would be worthwhile to look over your plumbing and water heater to make sure dissimilar metals aren’t directly joined together and that concerning levels of corrosion haven’t formed anywhere. If you notice either of these, call in a qualified plumber for further evaluation and repair or replacement. Simple things, like dielectric unions, can do wonders to prevent potentially dangerous and costly hazards, and knowing these things – however seemingly boring – can be a real life saver.

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Author: hillinspections

I am a Certified Professional Inspector (CPI) and the owner and operator of Hill Property Inspections LLC, based out of western Pennsylvania. I specialize in property inspections and environmental testing services and have a passion for helping my own clients and other families in learning to properly maintain their homes. I am an Army veteran, former State Farm Insurance Agent, and real estate investor with experience in all facets of real estate construction, transaction and insurance. I am also the founder and President of the Southwestern PA Chapter of the International Association of Certified Home Inspectors (InterNACHI) and an affiliate member of the Cambria-Somerset Association of Realtors (CSAR). View all posts by hillinspections