Rubber = Galvanic Corrosion?

[sailboy21]

While browsing the web for boat stuff (what else?) I ran across a fuel tank manufacturer that issued a warning not to use rubber in contact with aluminum. The reason stated, was rubber contains carbon which exists on the galvanic series, and is slightly more noble than passivated stainless steel.
I immediately thought of my stainless steel masthound for my inner forestay.
I had placed a rubber gasket to insulate the stainless from the aluminum. It had never occurred to me that I may have been creating a bigger galvanic cell! I removed the masthound and found zero evidence of corrosion after two years.
Has anyone heard of an issue with rubber against aluminum? I usually use HDPE as an insulating material, and religiously use tefgel on fasteners, but I had a sheet of generic black rubber gasket material handy at the time. Should I replace the rubber with a sheet of HDPE or leave it alone?

[Valiente]

I'll try to check this out in my Metal Corrosion on Boats book. I hope it's false, as I use rubber sheeting for this purpose in a few spots as well.

[artbyjody]

Originally Posted by sailboy21

While browsing the web for boat stuff (what else?) I ran across a fuel tank manufacturer that issued a warning not to use rubber in contact with aluminum. The reason stated, was rubber contains carbon which exists on the galvanic series, and is slightly more noble than passivated stainless steel.
I immediately thought of my stainless steel masthound for my inner forestay.
I had placed a rubber gasket to insulate the stainless from the aluminum. It had never occurred to me that I may have been creating a bigger galvanic cell! I removed the masthound and found zero evidence of corrosion after two years.
Has anyone heard of an issue with rubber against aluminum? I usually use HDPE as an insulating material, and religiously use tefgel on fasteners, but I had a sheet of generic black rubber gasket material handy at the time. Should I replace the rubber with a sheet of HDPE or leave it alone?

Certain rubber gaskets and shrouds do contain carbon... Carbon is actually a very good electrical conductor (Carbon Fiber for example is a great electrical conducer)..

So the marks are not that far off - you can minimize the effect / severely limit however... if you are attaching to another metal - lubricate it with silicon sealant which is not as conducive and will prevent contact of the two...If the boundary is there - due to the lower level in the rubber - you will be out of harms way....but it is not a myth it actually happens...

[KeelHaulin]

Could you post the link to that website that talks about it? I can't say unless I have read that article. Normally rubber is an excellent electrical insulator; and as such it would help prevent electrical current between dis-similar metals. If it is a specific type of rubber that they are concerned with it might be the reason for the recall.

Carbon exists in many, many non-conductive things; it is the type of carbon bonds (at the molecular level) that would determine it's conductivity. CF probably has some conductive properties; but you would have to be attached to the roving directly because the plastic that encases it is non-conductive.

[billangiep]

I think the more likely event would be moisture being trapped between the rubber and the aluminum tank causing the corrosion.

[Sasha_V]

It depends on the ruber. Vulcanised rubber would have the most activated carbon in it...but you would not use it for much boat related stuff anyway...

latex rubber is safe, as is silicone "rubber" and any number of rubbers that have achieved the same stability as vulkcanised rubber, but through chemical processes instead of heat.

All in all, I think you are safe. really.

[hphoen]

Carbon conducts electricity, true, but that has nothing to do with corrosion. The material has to be capable of participating in an electrolyitic reaction, i.e, giving up or receiving electrons from another substance., usually in the presence of water. I've never heard of elemental carbon being involved in an electrolytic reaction. It reacts, of course, but needs heat and an oxidixzer to get started (combustion).

If salt water gets trapped between rubber and an aluminum tank, you could get corrosion, but the only role the rubber would play would be holding the water on the surface of the tank.

[thekeip]

Instead of rubber, I commonly use Mylar, available in sheets of various thicknesses, at art supply stores. Five-mil (0.005") drafting Mylar is an extremely tough material and easy to cut and use.
Howard Keiper
Sea Quest
Berkeley

[Valiente]

See? Mylar sheets...something new I've learned today. I suppose you could cut up a blown-out composite sail as well!

[Sasha_V]

I use PET plastic... Works like Mylar, but is free and always close to hand (drink bottle material).