Mixing Copper and Steel Pipe & Fittings

Old 03-04-09, 07:33 PM
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Mixing Copper and Steel Pipe & Fittings

Here is a pix from another thread (not mine), which prompts a question:

I've heard it said that copper and steel should not be mixed - to avoid galvanic corrosion of dissimilar metals. True?

Most older domestic plumbing systems that started out with all galvanized pipe now have copper sections added on by plumbers making additions, etc. My plumbing system is like that, and I have not observed any problems.

My hot-water boiler system started out with a steel boiler, black-iron pipe, and cast-iron baseboards. But, thanks to a room addition, it now has two copper fin-tube baseboards and copper pipe feeding them, installed by professional, union plumbers.

My system has a brass pressure reducing valve and a brass pressure relief valve, both connected to steel pipe.

No dielectic unions anywhere in the system.

A brand new cast-iron hot-water boiler is likely to be connected to a copper hot-water heating system and copper make-up pipe from the city water system.

My city water comes in via a copper pipe, to the meter, and from there it is galvanized steel.

Old 03-05-09, 07:42 AM
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Depends on who you ask.

Some standard reference sources (Ex: "Modern Hydronic Heating for Residential and Light Commercial Buildings") specify dielectric unions for dissimilar metal junctions on closed loop systems.

Some other authorities argue that you should not use any device which include elastomers (O rings, gaskets, etc.) in such system as the elastomers are subject to hardening as they age, and instead recommend the use of bronze or brass components at such junctions.

The supporters of dielectric junctions then argue that new synthetic materials are much less no subject to hardening.

In my area dielectric junctions are rarely used on hydronic systems, and I've not observed significant problems as a result.

OTOH pretty much everyone agrees that domestic water systems, do require dielectric junctions, and I see many problems created when they are not present.
Old 03-05-09, 09:35 PM
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Just put a brass fitting in between the steel/iron and copper. Dielectrics shouldn't be needed in heating systems since there shouldn't be air in the pipes.

That picture looks like excess flux, leaks and or air are factors.
Old 03-07-09, 03:25 AM
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depends on what type of water is in the pipe..

For a closed system, like a hydronic, all the oxygen leaves the first ( or second) time the water is heated, so no corrosion, unless you are constantly refilling because of a chronic leak.

drinking water, which is always fresh in from the street, is filled with dissolved oxygen, so lots of corrosion if dissimilar metals touch
Old 03-07-09, 02:35 PM
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When I was quite young and rather ignorant of such things I built a hydronic heating system using black steel pipe along with copper thread adapters to bronze Monoflo tees which then went to copper piping and copper finned convector baseboards. From the baseboards to the black steel was copper tubing and then a copper thread adapter to the steel. There was never any discernible corrosion of either the copper, the bronze or the steel in the following twenty five years.

I'm not saying this was the correct way to do this, just that in my particular case it wasn't a problem. The system used straight Seattle water for the first several years and was opened for inspection every year with a new charge of water added. For the first ten or twelve years no water treatment was used although I did use a molybdate/nitrite compound in the later years. I have no knowledge of what happened after I sold the house in '98 other than many years later while driving through the old neighborhood I noticed the house had been removed and a new multi-occupancy building had been built on the site. Sure wish I could've taken the boiler.

One thing about dielectric unions...I've never seen one that didn't have corrosion of some kind all over it after a few years of service.
Old 03-08-09, 05:44 AM
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Keep the oxygen out of the system and you should not have problems.
Old 03-09-09, 07:14 PM
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Oxidation and galvanic action are two entirely different things. Galavanic action is electrolysis, and is caused by a current being generated between two different metals (like the old Voltaic battery piles..) Galavanic action does not require oxygen.

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