dielectric union.

[gfitzgerald]

Over the years I have seen my plumbers doing re pipes for me use dielectric unions as well as brass nipples to join cooper to galvanized. I have never been called on the brass nipple. I am not sure it is per code or not. I had an inspection today that had close nipples and the ones I have had done used at least 3" nips. There was no sign of corrosion on the connection.

[Bob Elliott]

Interesting question.
Looking around at all the forums ,the talk is that brass is more compatible with steel than copper . Apparently there is still some electrolysis going on,though at a slower rate.

Found a galvanic chart for compatibility that demonstrates what I said.

As a code question it may depend on locale.

http://en.wikipedia.org/wiki/Galvanic_corrosion

[gfitzgerald]

I guess I can't recall ever seeing a city inspector crawling under a house so maybe thats why it was never called out