Reaction between copper and reinforcing steel

[BubbaJ]

I have a project where it is proposed that copper grounding conductors will be compression crimped to a continuous loop of reinforcing steel in the building foundation. While the electrician seems very comfortable with the idea of the connection of the dissimilar metals, the communications engineering firm is not familiar with the system and has raised a red flag regarding possible corrosion of the reinforcing steel.

I am not familiar with the process either and would appreciate a little education on the matter or websites where I may conduct my own research.

Thanks.

 

[strider6]

Bubba,

When you connect two dissimilar metals, you can have what is called galvanic or bimetallic corrosion due to the different electrochemical potential of the materials.
In order to have corrosion you need to have an electrolyte in which the two metals are immersed. The electrochemical potential depends on the type of electrolyte, eg in sea water is different from potable water.
Copper and Carbon steel, the reinforcing steel are usually a carbon steel materials, if connected and immersed in an electrolyte will give you galvanic corrosion, copper will be cathodic and not corroding while carbon steel will be anodic and corroding.
In your case you need to define if there is the possibility that at the interfaces between the two metals there could be water, maybe condensing humidity or rainy water.
If you need more look in this page for basic of bimetallic corrosion & galvanic series of metals:

http://www.corrosionist.com/corrosion fundamentals.htm

hope this help

Strider

http://www.corrosionist.com

 

[Metalguy]

If the area gets wet simply coat both Cu and Fe. The Cu cathode will be tiny compared with the large anode, so there shouldn't be much of a concern.

"When the eagles are silent, the parrots begin to jabber."
Winston Churchill

 

[BubbaJ]

The connection will occur in the concrete of the foundation, so yes, there will be moisture present as water is necessary for the hydration process.

 

[strider6]

In my opinion if you have to coat, then coat the cathodic part of the galvanic cell, the copper.
If you coat the anodic part, and you have a defect in the coating then there will be a very small anodic area where all the current will flow and corrode very fast.

regards

Strider

http://www.corrosionist.com

 

[BubbaJ]

We recently received info on the clamp to be used, Burndy Hyground. These clamps say they come precoated with Penetrox, an oxide-inhibiting compound with homogenously suspended metal particles.

So it is my understanding that the Cu and Fe will not physically be in contact with one another.

 

[EdStainless]

Is this for a ground? Why would anyone suspect that the reinforcing steel in the foundation is actually grounded?
This is why you use heavy Cu plated steel ground rods and drive them 8' into the earth.

= = = = = = = = = = = = = = = = = = = =
Rust never sleeps
Neither should your protection

http://www.trent-tube.com/contact/Tech_Assist.cfm

 

[BubbaJ]

There is a ground field. The foundation and precast concrete wall panels are being grounded due to the sensitivity of the equipment located in this building and besides the water tower, it is the tallest building around and the owner feels it will be a lightning rod. I do not know the intricacies of the grounding design, nor do I want to know, there are already enough "cooks" involved in that portion of the project.

My concern is regarding possible galvanic corrosion of the connected dissimilar metals, not the grounding.

 

[unclesyd]

Our entire site has a grounding grid that connects all structures. There are numerous connections to the reinforcing steel on the first floor. All of the connections between the steel and Cu ground wire are CAD welded. The only problems I've seen have been were the Cu wire was exposed and our process (nitric) got after the Cu.

 

[Metalguy]

>"If you coat the anodic part, and you have a defect in the coating then there will be a very small anodic area where all the current will flow and corrode very fast."<

No, because most or all of the cathode is coated.


"When the eagles are silent, the parrots begin to jabber."
Winston Churchill