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S/S to Steel Electrolysis and Corrosion

 

My boss is concerned about welding of a S/S cleat to 1/2" Steel plate, welding to a Steel Bulkhead, then painted. What are the chances of Electrolysis & Corrosion?

Tim DeVargas
USCGC Decisive - Pascagoula, Mississippi

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A battery is built by placing two different metals in a conductive solution called an electrolyte. As soon as you connect wires (a conductive path) from the battery to a load (such as a lightbulb), the more active of the metals begins to corrode (oxidize or go into solution), releasing electrons to flow and power the lightbulb. In a standard carbon-zinc battery, for example, the Zinc metal (Zn⁰) begins to coorrode into Zinc ions (Zn⁺⁺), releasing electrons that flow through the wire towards the carbon rod.

Any time you have two dissimilar metals, a solid conduction path provided by the metals touching, and an ionic path provided by moisture, you will have some galvanic corrosion because you have created such a battery, as illustrated:



While dissimilar metals are often connected in a dry office or home environment, exposure to moisture, especially salt water, is a different matter. The welds and/or the steel around the welds are very likely to corrode excessively because paint really isn't impermeable.

Ted Mooney, P.E.
Striving to live Aloha
(Ted can offer longterm or instant help)
finishing.com - Pine Beach, New Jersey

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