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Galvanic corrosion in air

Galvanic corrosion in air

Galvanic corrosion in air

(OP)
Are there any resources / standards that provide clear recommendation on which situations (which environments, how dissimilar the metals, practical mitigation methods) for galvanic corrosion in air? (It seems that salty, humid air is the major use case).

Thanks, David

RE: Galvanic corrosion in air

Do you have a site or condition in mind?
The US Navy publishes guides on coastal structures.
Just remember, if it is dry it will not corrode.
And you have to think about inside the building also hen there is a chance for condensation.

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P.E. Metallurgy, consulting work welcomed

RE: Galvanic corrosion in air

(OP)
It's machinery, and the component in question is a rotating carbon steel shaft rigidly coupled to a stainless steel (2205 this week) shaft.

The environment is salty coastal humid air. The equipment won't be subjected to salty mist but I do imagine a bit of salt could accumulate and condensation could make it salt water. These parts will be protected by solid (not perforated) brass machinery guards, which should help. It's a guess how all of that will add up to whether it lasts 20 years as required.

I did find some info from the Navy but not an ideal source - if you have a specific reference in mind I'd appreciate it.

RE: Galvanic corrosion in air

Can it be coated in cosmoline or some other self-healing corrosion inhibitor? Gelled-calciun sulfonate is a new tech hitting the market right now.

RE: Galvanic corrosion in air

What coatings have you looked at?
You could look at the multi-layer Zn rich coating systems.
Or a sprayed Al system with a seal coat.

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P.E. Metallurgy, consulting work welcomed

RE: Galvanic corrosion in air

(OP)
We currently cosmoline this piece of shaft. The customer would need to re-apply it regularly. I've considered electroless nickel plating, because it's thin enough it will not ruin the precision machined fits.

We might propose converting this shaft to 316L S/S but adding "another" material to the question might backfire. (It appears that 316L is similar to 2205 in galvanic potential but I don't have firm data yet)

RE: Galvanic corrosion in air

EN would be a good option. Over a long time you may still get some pin points of rust but most of the surface would be protected.
Like all plating there will be pinholes and cracks.
You can bake EN after plating and it gets harder.
How much depends on the phosphorus content.
If it is being put onto steel it should be baked anyway for hydrogen control.
If this shaft sees much load the very low strength of 316 would be an issue.

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P.E. Metallurgy, consulting work welcomed

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