Why the joints between materials matter
When copper is joined directly to galvanized steel, the two metals in contact with water set up galvanic corrosion. The steel side tends to corrode faster near the joint, which can narrow the pipe and eventually leak.
A dielectric union or similar transition fitting separates the two metals so they are not in direct electrical contact. Many older repairs were made without one, or with a fitting that has since failed.
Plastic pipe spliced into old steel or cast iron has a different weak point: the connection itself. Couplings that are not rated for the materials, or joints that are not supported, can loosen or leak over time.
Where to look
Common transitions and what to check
| Transition | What can go wrong | What to ask |
|---|---|---|
| Copper to galvanized | Corrosion at the steel side of the joint | Is there a dielectric fitting, and is it in good shape? |
| PEX to galvanized | Rust from the steel reaching new fittings; thread wear | Should the remaining steel nearby be replaced too? |
| Plastic drain to cast iron | Loose or unsupported coupling | Is the coupling rated for both materials and properly supported? |
| Cast iron to clay at the foundation | Shifted or open joint letting in roots | What does the camera show at that point? |
Quick facts
- Galvanized
- Dull gray steel with threaded joints; a magnet sticks.
- Copper
- Reddish-brown with soldered or pressed joints; a magnet does not stick.
- Dielectric fitting
- A transition that separates dissimilar metals in a water line.
- Typical clue
- Green or white crust and rust stains at a joint between materials.
Questions to ask a plumber
- How many transitions between materials are in my system?
- Do the existing ones have proper fittings?
- Would replacing this joint solve the problem, or is the steel around it failing too?
- If you add new pipe, how will it connect to what stays?
Common questions
Is it wrong to mix pipe materials?
Mixed materials are common in older houses. The concern is how they are joined. Proper transition fittings and support make mixed systems far more reliable.
Why is there green crust on a pipe joint?
Green or white crust usually means a slow leak with mineral buildup. It is worth having the joint checked before it gets worse.
Can a transition fitting fail?
Yes, like any fitting it can wear or leak with age. Inspect older transitions during any plumbing visit.
General information for Old Towne Orange, not a quote or professional advice. In an emergency, call 911.