Galvanised corrosion by indirect contact

[IGSAM]

Hello,
I work in the mining industry, and it is not uncommon to see in the process plants stainless steel equipment’s with inlets & outlets of carbon steel system.
For example, a stainless-steel tank with a plumbed carbon steel inlet and carbon steel outlet. The physical contact between the two flanges is protected by a gasket. If there are no direct contact, can we still expect galvanized corrosion due to fluid flow ?

Thank you,

 

[EdStainless]

Considering how difficult it is to keep the flange and bolt isolation intact, and the chance for debris or corrosion products to bridge the joint on the inside there is likely to be some galvanic corrosion.
But the better the isolation the less you will have.

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P.E. Metallurgy, Plymouth Tube

 

[Compositepro]

Galvanic corrosion requires that electric current must flow in a loop from one metal to a different metal through an electrolyte, and then return to the first metal by direct metal to metal contact. There are many other types of corrosion however.

 

[Dhurjati Sen]

Dear IGSAM,

What is the service, by the way? We do not have Galvanic Corrosion charts for services and CS & SS fall close enough in most to cause much concern.

However, Carbon pick-up by the SS could lead to other forms of corrosion like sensitization which again depend on the service conditions to take place.

Regards.

DHURJATI SEN

https://www.nace.org/people/dhurjatisen

 

[IGSAM]

Hi All,

Thanks for you answers. I would be interested in knowing the other type of corrosion that could happen so here are some specific examples, all those example the connections are flanged :
* Water Tank in stainless : Water inlet & outlet in C.S. : Fluid Water 30C
* Water line in C.S. with stainless steel valves : Fluid Water 30C

Thanks,

 

[Dhurjati Sen]

Dear IGSAM,

You need to be more specific about 'water'.

What is the chloride content of the 'water' ?

Anyway, it seems that the CS piping is more prone to corrosion than the SS tanks.

So you could be quite comfortable with the SS tanks.

Regards.

DHURJATI SEN

https://www.nace.org/people/dhurjatisen

 

[cap1a79]

In principle, galvanic corrosion will never happen absolutely in case there is no physical contact between two different metals.Actually, for the corrosion to occur, there should be corrosion loop cycle formed that anode (physical contact) -cathode- electrolyte(such as water) - (back to) anode. If the cycle is broken, galvanic corrosion will not occur definitely.


Lee SiHyoung,
WorleyParsons Oman Engineering,

 

[EdStainless]

For galvanic corrosion, like all forms the conductivity and temperature of the water are important.
Without galvanic corrosion of the CS begin accelerated by the SS the next things to look at are flow related (erosion-corrosion) of the CS and pitting of the SS.
Pitting of the SS will be greatly accelerated if there are are cervices formed.
These can either be mechanical crevices (bolted connections) or due to deposits on the surface.
Having corrosion products from CS settle onto SS will very likely lead to localized pitting.
And then there are various corrosion forms driven by microbiological activity.

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P.E. Metallurgy, Plymouth Tube