Galvanic corrosion

Burdy · Aug 13, 2003

There appears to be a problem with Duplex Stainless Steel and Graphite corroding when in contact with sea water.
As requests for products with this combination have statements that the graphite must have a barrier on the graphite to prevent contact with the water, I believe that this is to try and stop Galvanic corrossion!

Is anyone aware of any actual documented failures or tests where this is confirmed.
Any assistance in this area regarding these or any other metalic material in combination with Graphite causing the same effect would be appreciated.
Many thanks
B

TVP · Aug 13, 2003

Graphite is cathodic (more noble) to every other structural material. Galvanic corrosion in the presence of an electrolyte (saltwater) will be a significant issue. Use the following link to see how graphite compares to other metals in the galvanic series:

http://www.corrosionsource.com/handbook/galv_series.htm

Note: my guess is that a duplex stainless steel will be somewhere between the 3xx series alloys and Type 430 on that chart, but I'm sure mcguire will come along soon with more details.

PVRV · Aug 17, 2003

Three ways to stop galvanic corrosion, dont use dis-similar metals, ensure the absence of an electrolyte and isolate either surface in question (a barrier). If a combination (pair) of items 1,2 or 3 exist.

TVP is correct, we have used graphite as an inert anode we stopped a few years back and moved towards AL. At any rate, I am not aware of the configuration you have;or where and why graphite is being used. IF it is being used as a gasket, my only responce is why!

Regards

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Galvanic corrosion

Burdy

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