Galvanic corrosion between Ti Gr.2 and Duplex S31803

Galvanic Corrosion is not just related to the anodic index, or galvanic series, but you've to consider two other important factors:
- Relative ratio of the Areas of the two metals
- Electrolyte

As a reference for the potential of the two materials you can see :

"There is no major difference in corrosion potential between highly alloyed stainless steels and titanium."

hope this help

S.

Corrosion Prevention & Corrosion Control

Isn't the galvanic series based on salt water as the electrolyte?

As for the relative ratio of areas, I'm not quite following.
If I am considering a bolt and a nut, would not the ratio then equal to 1?

Thank you

By the way, I found a good site stating all the different variables :

what you usually find is the galvanic series in seawater but the galvanic series is not the same in all electrolytes and is different also for different atmospheric exposure sites( marine, industrial...)
If you have an electrolyte with low conductivity then the effect of galvanic corrosion are different.
there are many things to consider..........

Galvanic Corrosion

S.


Corrosion Prevention & Corrosion Control

In my particular case, the electrolyte is in worst case salt water. Thank you

FC2008,
Beware of using Ti coupled with duplex in nut/bolt combinations in marine environments. Crevice corrosion of the duplex stainless may result.

Crevice corrosion at the contact is the real risk.
The published galvanic series is in FLOWING seawater. Stagnant crevice conditions are a more series situation.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

Let's see if I understand all of this.

There is no major difference in corrosion potential between highly alloyed stainless steels and titanium. []

I can't find duplex in the galvanic chart, nor can I find its Anodic Index, but I assume they are close to each other as long as duplex is passive.

But, because I am using Duplex as the nut, my construction will be prone to crevice attacks (stagnant seawater), and thus I have to look at the duplex as active. When in its active state, they are far apart in the galvanic chart and should not be used together.

Am I thinking right?

Thanks!

It depends on what you mean for salt water. If it's seawater then a 2205 duplex can suffer from localized corrosion, usually in seawater a superdup0lex with PREN higher than 40 is specified, but if the content of chlorides if lower than seawater then it's possible that 2205 will perform well.
Another importatn factor is the operating temperature of you water.
See these graph from Outokumpu on Crevice behaviour of duplex and stainless steel. In my opinion you've to define exactly the temperature and cl- concentrations.

there is also a free software from NIDI to evaluate the possibility of crevice corrosion:




S.

Corrosion Prevention & Corrosion Control

In my case it's seawater. We've used S31803 duplex for ages with good results. Where there are threads in the construction O-rings have been installed to prevent seawater from entering.

Thank you very much for your time!