Iron to coppper

hot_rod

typically pumbing pipes would be galvanized, and yes you do need a dielectric break. Brass or bronze nipples would work. I hate dielectric unions :)

Copper to iron, or steel generally isn't a problem, especially in closed loop heating application. If you have steel or iron in DHW application, you generally get rusty water, at some point.

hot rod

Chris_16

Connection copper pipe to iron pipe

I am replacing some old iron plumbing in my bathroom that leaks. I want to use copper and was told I will need to use dielectric unions to join the copper to the iron. Why do I need them!! and and what if I don't use them? Some people said that the unions tend to leak.

Also I would like feedback on using teflon tape and or pipe thread compound? I seem to get alot of leaks when using teflon tape.

Thanks for the help,
Chris

John@Reliable_4

Chris, I use tape & dope. And never a leak!

Walt Risler

Dielectric unions

There is a reason they make these unions. Here is an explanation I found on the web.

If you recall from high school chemistry, two dissimilar (different) metals, when placed in an acidic solution, will create a battery. And one metal will usually erode away as the chemical reaction progresses. The other metal may have a buildup of new material, which may be a chemical combination of the eroded metal and the acid. Since virtually all domestic water is slightly acidic or slightly basic, this electro-galvanic action can occur in any metal plumbing system.

When copper and steel pipes are connected together directly, the "battery" has a path for electrical current to flow. (This current is tiny, and the voltage is not a safety hazard.)

If the current cannot flow, because there is no electrical connection (interrupted by the plastic insulators) then the "battery" never discharges. In theory there will always be a small voltage between the different metals. The metals do not erode.

heretic

Not usually a problem, for heating

The board consensus on this seems to be that there is not enough free oxygen in a closed heating system to allow galvanic corrosion to happen.

Looking at install pictures here, and most installs I have seen in person, it appears to be common practice to mix and match copper and iron, particularly in the 'near boiler' piping. Iron is much stronger for supporting pumps, manifolds, and such. Also cheaper in the larger diameters.

I have looked at many old installs where mixed materials were used, and have not observed any problems.

A steam system probably would have issues, but I cannot comment.

Now if you are talking potable water, there is tons of free oxygen, and trouble...

heretic

Had good luck with Block

This Hercules 'Block' sealant has performed well for me.

Alcohol cleanup is a nice feature, I think. Not very toxic as solvents go.
Also a good gasket maker. Similar chemically to Permatex Aviation Form-A-Gasket, but thicker.

http://www.herchem.com/Products/block.htm