Stop galvanic corrosion
1 of 2
Photo 1: A badly corroded joint
This dielectric fitting didn't provide enough
separation between the dissimilar metals,
allowing the pipes to corrode and clog.
2 of 2
Photo 2: A 3-in. dielectric nipple
The 3-in. plastic liner in this
dielectric fitting provides
a greater degree of separation
to keep the dissimilar
metals from corroding.
Whenever you join copper water lines to galvanized steel pipe, you should be concerned about the corrosion
caused by joining two dissimilar metals, called
“galvanic corrosion.” An electrochemical reaction
occurs that causes the steel pipe (in this case) to rust
and clog up. The dielectric fittings commonly available in home
centers (Photo 1) have a short plastic
nipple that keeps the metals from touching, but the
metals are still close enough to cause a reaction and
The solution is to use a special 3-in. fitting
called a “dielectric nipple” (Photo 2).
They're available for about $9 at plumbing supply
stores. A plastic liner
(3 in. long) inside the fitting keeps the metals far
enough apart so corrosion won't occur (as much!).