Dissimilar Metals

[Sunnyboy]

Hello all,
Mulling over an upcoming job and coming to an item that has me concerned. The client is planning to install some stainless steel framing and strut supports. This is for esthetic purposes only. We are planning to run standard EMT conduit with standard EMT compression fittings. For esthetic purposes we were thinking of using stainless steel for strapping purpose to match the rack etc. Our concern is of course galvanic action. It’s not a corrosive environment, but there will be some moisture and humidity at times. Will the stainless steel straps in contact with the galvanized EMT cause problems down the line? What about the galvanized EMT in contact with the clients stainless strut? Straps and strut aren’t fittings, I guess.
There also are plans for powder coated steel enclosures to be mounted to a stainless steel frame. I know the codebook talks about powder coated enclosures when referencing dissimilar metals though. Just worried about the future and want a rock solid install.
Any experienced advice would be appreciated. Thanks

 

[infinity]

Will the stainless steel straps in contact with the galvanized EMT cause problems down the line?

No. In a normal environment this isn't an issue.

 

[herding_cats]

Galv/zinc and 316 SS won't react.

 

[don_resqcapt19]

Galv/zinc and 316 SS won't react.

This table says otherwise. It says there is a risk where the voltage potential exceeds .2 volts. Zinc and stainless 316 has a voltage difference of .9 volts.

 

[winnie]

For galvanized vs stainless steel you need to consider area effects.

If there is an electrolyte present, the zinc will sacrifice itself to protect the (stainless)steel. That is exactly what galvanization is supposed to do!

But relative area matters. A stainless steel fastener on galvanized metal is totally fine, because you have lots of zinc protecting a little bit of exposed steel.

Put a galvanized fastener into a stainless steel item and it will corrode quickly (if other conditions for galvanic corrosion are present).

Depending on the atmosphere I might be concerned about corrosion to the galvanized conduit right at the edges where it touches the stainless steel.

You can get straps with plastic inserts if you really want to keep things separated for the esthetics. Or maybe you could wrap the points of contact in electrical tape. Just make sure you charge the client for the extra consideration. They are buying stainless steel for the looks after all.