Different materials for bolts and nuts regarding galvanic corrosion? 5

[tronics21]

Hi everyone

For the project I am working on, I am using a Titanium grade 5 threaded rod with S/S 304 plates and nuts.

I am concerned about galvanic corrosion. Both Titanium and S/S 304 are safe for the application environment(steam, salt water, etc) but I am not sure how they are going to work together.

Thank you for your time reading my post and I would appreciate any comment.

Thanks!

 

[TVP]

In general, when the potential difference is less than 0.25 V, there isn't a large driving force for galvanic corrosion. Here is one reference to review:

http://esmat.esa.int/Publications/Published_papers/Bimetallic.PDF

Keep in mind that Type 304 stainless has limited resistance to pitting and crevice corrosion in seawater, especially if the temperature is > 25 C. Coupling it to Ti definitely will not improve things.

 

[tronics21]

Thanks TVP,
According to the reference the difference in Titanium and S/S304 is only 0.03V.
I suppose I don't have to worry about galvanic corrosion.
I will look into crevice corrosion in seawater for SS304.

 

[EdStainless]

In salt water, not even sea water, the 304 will be in an active corrosion condition and being coupled to the Ti will accelerate the corrosion.
Probably not a good combination.

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Plymouth Tube

 

[TomDOT]

Is 304 even going to stay passivated with salt water exposure? My understanding is that the boat guys avoid 304.

 

[EdStainless]

No, 304 won't stay passive. Between the salt water and the Ti it will shift of about -.50V, more than enough to drive serious galvanic corrosion.
You won't just corrode the nuts you will also hydride the Ti bolts. At first this just makes them stronger but eventually you will loose a lot of the ductility.

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Plymouth Tube

 

[tronics21]

I did more research and expressed my concerned to my supervisor.
He said the product won't be used under the environment where salt water is present.
But other senior engineer is going to take a look at the paper to make sure whats going on.
Thank you for the comments!