Corrosion of coupled dissimilar materials (metals)

[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 current flow is applied.

Attached a photo of the bolt

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

Luigi

 

[Dhurjati Sen]

What made you notice the thinning?
As the final structure is PVC coated, you ought not to have worried a bit regarding Galvanic corrosion!

DHURJATI SEN
Kolkata, India

 

[Luigi C.]

Hi Dhurjati,
Thanks replying me.

Probably from the photo I loaded the crossection reduction isn't so highlighted. I'm going to load another one.

I'm totally agree with you, PVC coating gets the spline insulated, so the oxygen we suppose that cannot reach the joint.

Which corrosion phenomena could be involved in your opinion?

Luigi

 

[mrfailure]

Not likely, but is it possible these were overtightened to the point that they exhibited yielding?