Galvanic Corrosion and Electrolyte in piping 1

[PROF18]

Hello folks,
When speaking about galvanic corrosion in piping when connecting different flanges material (Carbon steel and SS for example), and coming to the point of Electrolyte, what is the Electrolyte here? The media inside or outside the piping?

 

[TugboatEng]

It can be both. For myself working in the marine industry, the electrolyte is typically outside of the piping. In most other cases the electrolyte is inside.

 

[PROF18]

@TugboatEng
Thanks for your answer, can you explain more how in the case of dissimilar flanges material be the electrolyte inside? as I think the fluid will not face the area of the dissimilar materials.

 

[mk3223]

Just to make sure that the electrolyte is the process fluid inside the pipe, which is connected by two dissimilar material flanges bolted together.

 

[PROF18]

@mk3223
Thanks for your reply, what I ask about, inside the pipe the process fluid will not face the area where dissimilar material are present, isn't it?

 

[TugboatEng]

Properly selected, your gasket will prevent the process fluid from contacting the faces of the flanges.

You are asking a very complicated question so the only correct answer we can give is, "depends".

But I can tell you authoritatively that if you have a large ratio of steel piping to stainless you'll probably be ok. If you have a large ratio of stainless to steel you will not be ok.

 

[EdStainless]

There will be an area inside the gasket where each flange material is exposed.
Bolts electrically connect them on one side and the electrolyte (conductive working fluid) on the other.
You have a circuit and therefore likely galvanically driven corrosion.
They don't need to be wetted where they touch each other.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[Chumpes]

Hello
For your information, another common word that may replace the term "electrolyte" is "water".
Free water (liquid phase) is the most common electrolyte that one can meet.
Regards

 

[saplanti]

If you cannot get away from it, you have option to use “flange isolation/insulation[sup][/sup] kit”. Just search it on Google, lots of information about the kits from several suppliers.

Some more information:

https://www.eng-tips.com/viewthread.cfm?qid=391829