When joining dissimilar metals in a cold water system, what device helps mitigate galvanic corrosion?

• A. Dielectric unions are decorative fittings with no functional impact.
• B. They are used to join same metals only.
• C. They prevent galvanic corrosion when joining dissimilar metals.
• D. They act as check valves.

Answer: (C)

Galvanic corrosion happens when two different metals are connected in the presence of water, creating a tiny electrochemical cell where the more anodic metal tends to corrode faster. Dielectric unions place a non-conductive barrier between the two metals, usually with an insulating sleeve or gasket, so electrons can’t flow from one metal to the other through the joint. By breaking that electrical path, they stop the galvanic reaction and protect the metal that would otherwise corrode quicker. This is why dielectric unions are used when joining different metals in a cold water system. They are not decorative, not limited to just same-metal joints, and they do not function as check valves.