dialectric union

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Is a dialectric union required for a cast iron to copper connection or is it only for a galvanized to copper connection?

Thanks, always, Arlene

ScottMP

Arlene

If your talking about a closed heating system my answer is no.

I have seen them installed on heating systems, but have never used them and have never had a problem. No one in my area use's them. At all, even on hot water heaters. I am sure there are areas of the country that its necessary.

Scott

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Tom Meyer

Dielectric Unions

Usually we've spec'd them between galvanized pipe and copper. Here's a more scientific explanation:

"Two dissimilar metals, when placed in an acidic solution, will create a battery. 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."

Senior Designer/Trainer
Precision Hydronics Corporation
www.precisionhydronics.com

Kritz_3

Dialectric unions

If you have two dissimilar metals there will be a galvanic
reaction, a electric (DC) current will be produced. That is
generated through a chemical reaction if the ph of the H2O is
more acidic the reaction will be more substantial, a zinc coat
ing will also increase the reaction. So at the end of the day, eventually there will be a leak at the connection it is just a matter of time. By the way the reaction was named after Luigi
Galvani a Itailian physiologist in the late 1700's.

ScottMP

Kritz ?

So the question is , How long is a matter of time ?

If its longer than the life time of the equipment its attached to than its moot.

I started in the Trades in 1980, and have yet to see a corosion of a joint in a closed loop heating system due to dissimilar metals. I've seen joints fail from improper joining techniques, but I don't believe galvanic action in a closed loop is a problem.

I am open to being proven wrong

By the way I looked up dissimilar in the dictionary and its not there. Are we all spelling this wrong ?

Scott

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Kritz_3

dissimilar

Well I do believe the correct spelling is dissimilar, this is found between 'a' and 'zyzzyva'. As for corrosion in closed loop systems I have seen this action take place. If you can wait till monday I'll post a photo from a job I'll be going to
in Queens,NY.

Steve

Tom Meyer

I've seen it too.

It looks like the crusty growth on an old battery.

And yes, "dissimilar" is spelt correctly.

Senior Designer/Trainer
Precision Hydronics Corporation
www.precisionhydronics.com

hot_rod

For code compliance or piece of mind ?

Here is a simplified galvanic chart, and a in depth one. (not sure I could identify all these metals and alloys by sight The closer together the materials the better they get along.
Also the relative area effect plays in, the size of the iron to copper. For example an iron bolt in a large copper plate would corrode quickly, whereas a copper bolt in an iron sheet would corrode very slowly. This would be considered the case when connecting copper to iron boilers.

Lots of other factors play in such as the liquid and it's flow rate inside the connection, dissolved O2 in the fluid, ((water heaters that see contineous fresh water,) protective films inside the pipe connection, etc.

Most code books require a dielectric connection on water heater installations. I prefer brass or dielectric nipples and copper adapters. Or copper union, if the inspector really wants a union connection. The dielectric unions tend to corrode shut my experience has shown, especially in hard water conditions.

I have never been called on the lack of dielectric unions on boiler installs, and feel they are not necessary. Just depends on how the inspector reads the codebook.

I'd insist on some sort of "connection" at the water heaters, especially with a mix of copper and galv, but not worry about boiler piping, on your inspection report.

www.copper.org has lots of material on this subject, if needed.

hot rod

Steve Eayrs

Dialectric unions

We have most likely tore out way more dialectric unions on boiler systems then install. The rubber gaskets get old, hard, and crack and become the biggest source of leaks and air problems. We have instead installed brass mip x c unions, and don't have the same problems.

We do still use them for fresh water system, but I would love to see a better made dialectric union.

Why can't they make one that doesn't need gaskets replaced? Any I hate those old brittle plastic isolation rings. I have a hard time believing their isn't someone out there making one that can be a few years old and still be soft enough to not break, when you touch it.
Is there?

Steve

[Deleted User]

Where does yellow brass

fit into the picture. I know it's an alloy, and I'm told it's benign to both copper and ferric irons.

I've got pictures of di-electric unions that were properly installed and within the life expectancy of the water heater they are so corroded that I'm amazed that water even flows through them.

Whazupwidat?

I've also seen the clear flow nipples corroded in the same manner, not nearly as many nearly as bad, but they too have a corrosive element to themselves.

Dr. Geoorge Lof, world famous solar hydronician/professor/engineer once told me that, under the right conditions (low pH with liquid electrolyte) a dielectric union in and unto itself is an excellent battery. Even with all the washers/sleeves, it still has enough of an electrical path potential that sets up an internal exchange of ions. He said you could probably power an LED with it... There ya go, there's an idea, corrosion potential lights! Huh, Buderus already does that....??? Oh...NEVAH mind:-)

ME

Joe_30

brass works?

I have been repeatedly told that putting a brass connector between iron pipe and copper pipe in a closed loop heating system minimizes galvanic action. So, have done so. Is this myth?

Mike T., Swampeast MO

Being about 20% zinc and 80% copper (I believe) yellow brass would logically make a good transition from iron to copper as it would [seem] to fall between both in the transition from iron to copper.

This galvanic table [seems] to verify...but I am CERTAINLY NOT a metallurgist--but at least I spelled it right off the top of my head.

hot_rod

you bet your brass

The type of brass used depends on the application. Brass is a copper zinc alloy. Alpha being brass with a 64% or more copper, beta 60% or less. Some brasses are alloyed for casting, others for machining. Leaded brass was a common alloy used for faucet and valve bodies. Excellent machine ability. Not sure what the current alloy is since the "lead scare"

I think the nipples we get at the supply house are probably bronze, a copper and tin alloy, usually a darker color and better matched for iron to copper transtions. In addition to various brass and bronze types there are a ton of different tempers. Again based on the final use of the material.

Add to the mix imported brass and bronze. I'm not sure how to tell the blend in some of those materials. Probably not ASTM rated.

Most of the faucet and door hardware brass is cast overseas these days. I think they melt down old military rounds

hot rod

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[Deleted User]

You're OK...

yellow brass is a recognized means of dielectric isolation. I was just wondering where it would fall on the charts.


ME