Summary for galvanic corrosion stainless steel galvanized Discussion
Galvanic corrosion between galvanized iron and stainless steel is likely if the metals are in constant contact and moisture is present. In response to Fred Stein Rider Hunt’s question, Ted Mooney explains that galvanic corrosion needs three things: a difference in electrochemical potential, an ionic path for current flow, and a metallic path. He compares it to a battery: once the metals are connected and wet, the circuit is complete. Because zinc on galvanized steel is very active and stainless steel is relatively noble, the potential difference is strong, so corrosion can occur. The practical takeaway is that direct contact alone is not the whole issue; the real risk rises when the joint is wet or otherwise able to conduct ions.
Q. If stainless steel is in constant contact with galvanized iron will electrolysis result?
Fred Stein
Rider Hunt – Las Vegas, Nevada
2006
A. Galvanic corrosion requires a difference in electrochemical potential between the two metals, an ionic path for electrical current flow (corrosion), and a metallic path for electrical current flow. Picture a battery–it’s good to go as soon as you connect wires (as soon as you complete the metallic path).
The zinc coating on galvanized metal is very active and stainless steel is relatively noble, so you have a strong difference in electrochemical potential. If they are wet you probably have a good ionic path. If the materials are in contact you have the metallic path.
Ted Mooney, P.E.
Striving to live Aloha
finishing.com – Pine Beach, New Jersey
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2006
Q. There are applications in HVAC that require an isolation of metals for reactivity.
There are common practices that are not allowed in specifications to a particular project.
My question is this, ” If I weld the dissimilar metals solid to each other does the reactivity diminish to a point of longevity?”
Jerry Sirek
– Spokane, Washington, USA
April 25, 2012
A. Hi, Jerry.
Unfortunately, absolutely not. Galvanic corrosion forces will only be more reliably bad.
Galvanic corrosion forces are the same system as a battery and lamp, and consist of the following arrangement: two different metals (like the zinc/carbon or nickel/cadmium in a battery), a wet ionic path (the black glop in a battery, or the salty water bridging your two materials), and the metallic connection between the two metals (a wire and lamp, or your solid welded connection).
One way to stop galvanic corrosion is to electroplate or galvanize the entire weldment with a single material, but this may be impractical in your situation. Painting it would not be as effective, but would help somewhat.
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com – Pine Beach, New Jersey
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April 25, 2012