Symptoms
- Unusual corrosion concentrated right at a copper-to-steel connection
- Greenish or rusty buildup specifically at that joint
- Leak developing at a transition point rather than along a straight pipe run
- Corrosion is worse there than anywhere else in the system
Likely causes
- CommonMissing dielectric union between copper and steel pipe (galvanic corrosion)When two different metals touch with water present, an electrochemical reaction accelerates corrosion at that junction unless isolated.
- CommonDielectric union installed but its internal insulating component has failedThe plastic or rubber insulator inside these fittings can degrade or be bypassed over time, allowing the reaction to resume.
- PossibleStray electrical current from grounding issues in the homeIf household wiring is grounded through the plumbing (older practice), stray current can accelerate corrosion at metal transitions.
What to do
- Identify any spot where copper pipe connects directly to a steel or galvanized fitting, such as at a water heater's inlet and outlet nipples.
- Inspect for a dielectric union (a fitting with a distinct plastic or rubber insulating gasket) versus a direct metal-to-metal threaded connection.
- If no dielectric union exists at a copper-to-steel junction, plan to install one during the next repair or water heater replacement.
- If a union exists but corrosion is still occurring, it may have failed internally and should be replaced.
- Have an electrician check whether your home's electrical system is grounded through the plumbing, and if so, discuss proper grounding alternatives.
- Address any active leak at the corroded junction promptly, since this type of corrosion tends to progress faster than general pipe aging.
- When replacing a water heater or doing other work involving dissimilar metal connections, always specify dielectric unions to the installer.
Tools and parts
- Wrench
- Pipe cutter (for pipe section replacement)
Dielectric union fittingSearch: “dielectric union fitting”
When to call a pro
Call a plumber to install or replace a dielectric union, and an electrician if you suspect the plumbing is being used as an electrical ground path.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.