48391

Compatibility of aluminum and galvanized steel [Philippines] 

April 3, 2008

I would like to ask if I still need a nylon separator between hot galvanized steel and aluminum surface where there is a direct contact between the two? where in fact there is a expected water running through it.

I am reviewing a desing drawing with the above condition. this is for the facade shop drawing. please help.

Mai Saxor
engineer - Philippines

Mai
I'm an architect and asking a similar question here in UAE of anodized aluminium supported on galvanised steel frame. Here it's hot and often dry heat but summer creates high humidity and the site is right on the Arabian Gulf.

I think a nylon separator is necessary but the question may be a bigger one than only contact. I understand that rain water can connect the two metals and still produce corrosion.

Can anyone confirm or refute this? Should I be using powdercoating instead of galvanising?

Regards

Matt Brindley

Matt Brindley
architects - Al Raha, Abu Dhabi, UAE

Hi, Matt. Galvanic corrosion is not the only kind of corrosion, so avoiding galvanic corrosion doesn't guarantee that a material will last indefinitely in an exposure condition, but it certainly helps.

You will not get galvanic corrosion if the parts are not metallically connected. That's my understanding anyway.

A galvanic corrosion cell works like a battery connected to a lightbulb. Two different metals like in the battery, salty conductive water or moisture like the conductive glop in the battery, and a metallic connection like the wires and light bulb. A battery may last only a short time powering the light bulb, as metal moves from anode to cathode to produce the power; but the battery will last a long time on a shelf because the metal cannot move from anode to cathode without the wiring.

Positively charged metal ions can travel though watery solutions but electrons don't. Metal can't electrochemically move from one place to another without a path for the positively charged ions (moisture) and a path for the electrons (metallic connection).

Regards,

Ted Mooney, P.E.  finishing.com Brick, NJ