Cast Iron to Copper Corrosion?

Larry C_13

If the heating system is STEAM and the piping in question will contain steam, stop right there. The difference in the expansion rate between iron and copper will cause mechanical failure. Otherwise, I would reconmend using a brass fitting of some sort between the iron and the copper.

Larry C
Home owner not heating professional.

k

I've read a number of different opionions about how to connect copper and cast iron pipe in a heating system. I'd obviously like to avoid corrosion long term. What is the best way to go? Can I connect CI to copper and have it not corrode and leak? Shoud I use brass adapters or even dielectric couplings to avoid any issues?

k

It's a hot water system so no concern there. I'll see what I can find in brass to go from 1-1/4", 1", 3/4" MIP and FIP to copper 3/4" SW.

klaus

Valves or Dielectrics

I personally like to use brass ball valves in those spots. If it's a spot that could use a valve anyway they make excellent adapters. I try to shy away from dielectric unions because invariably they will leak. However deielectric nipples on the other hand are great. They are usually galvanized and have a plastic coating on the inside.

Good luck, Rich L

k

I am using brass ball valves on each supply and return. I had not though of using them to isolate the CI and copper. I'd still need to find adapters to go from the three different sizes of NPT threads to the ball valves...

Thanks for the idea though.

Unknown

I don't agree

with that Larry . A properly sealed and tightened fitting , any type rated for this purpose , will last for decades . I see copper to thread adapters often in steam headers that haven't leaked for at least that long . It's not my material of choice , but we do see it often .

Dielectric unions are not needed on hot water heating systems in my opinion . Copper adapters into cast iron , steel , aluminum ..... etc. will work perfectly fine . Matter of fact , I've yet to see a dielectric union on a water boiler . I've yet to use one .

Bonafide way to guarantee the fitting won't leak ? Use whatever joint compund you're comforatable with , tighten it up , then heat it up . While it's still hot , retighten .

klaus

You're welcome Glen!