Galvanic corrosion between Ti Gr.2 and Duplex S31803

[FC2008]

Hey,
i'm trying to prove that there will be no galvanic corrosion between the materials mentioned in the thread title.
Looking at the galvanic table I see that Ti and Stainless steel are quite close. I don't see duplex beeing listen though.

Anyone here know the anodic index of Duplex S31803 steel? I have found that titaion has a AI = 0.30V, but am unable to find it for duplex.

Thank you

 

[strider6]

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."

http://www.outokumpu.com/pages/Page____26793.aspx

hope this help

S.

Corrosion Prevention & Corrosion Control

 

[FC2008]

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

 

[FC2008]

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

http://www.corrosion-club.com/galvanic.htm

 

[strider6]

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

 

[FC2008]

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

 

[stanweld]

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

 

[EdStainless]

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

 

[FC2008]

Let's see if I understand all of this.

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

http://www.outokumpu.com/pages/Page____26793.aspx

]

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!

 

[strider6]

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.

http://www.outokumpu.com/pages/Page____26793.aspx

http://www.corrosionist.com/Pitting_Crevice_Corrosion.htm

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

http://www.nickelinstitute.org/index.cfm/ci_id/10646/la_id/1.htm

http://www.corrosionist.com/Software_for_Corrosion_Prediction.htm

S.

Corrosion Prevention & Corrosion Control

 

[FC2008]

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!