Corrosion of dissimilar materials

[Luigi C.]

Hi everyone,
I'm currently indagating aspects related to plating racks structure.
At this moment I'm looking for a solution or something that can help to find a precise answer to this trouble:

To make possible the coupling of a copper flat bar to the stainlessteel clips we need to use zinc plated bolts.
Practically, holes are drilled and threaded in the copper flat bar and clips are mounted using zinc plated bolts.

The problem is: We can notice, where the bolt is coupled with copper, an abrupt reduction in section of the bolt.


Consider this situation: The final structure is insulated with PVC coating, immerged in an acid solution at 55°C and a continous cathodic current flow is applied.

We can suppose the bolted joint isn't in contact with oxygen because of PVC coating, so I'm going to indagate stray current corrosion. I should be a good idea or not?


If anyone can help me I'd be very grateful.

Luigi

 

[EdStainless]

1. Your coating isn't a perfect seal.
2. Remove the steel, use either brass or SS bolts to fasten the rack.

There is no path for stray current.
All of the current has to flow through the parts.


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P.E. Metallurgy, consulting work welcomed

 

[Luigi C.]

Hi EdStainless,
Thanks replying me,
We noticed that coupling aluminum and a SS bolt there isn't a corrosion on over the bolt section.

Which corrosion phenomenon could be the cause of the zinc plated bolt?

I attach a photo of the bolt

Luigi