Galvanic Series - Corrosion Potential Data

Overview

This data is used to determine the best fastener materials. In the galvanic series of elements, shown below, any element to the left of the alloy you want to protect is anodic to it and can protect it sacrificially, while any element to the right is cathodic to it and can cause it to corrode galvanically in the presence of moisture.

The table is based upon flowing seawater and was developed for the purposes of determining which naval alloys can be used in seawater. You can use this to solve or prevent common corrosion problems in exterior construction.

Notice that Cadmium and Zinc are to the left of (i.e. anodic to) steels and so are used as a way of protecting them from corrosion since it sacrifices itself in place of the steel it protects. Notice also that Zinc and Cd are close to the Al alloys in galvanic potential, whereas the stainless steels and nickel alloys are far to the right. This is why it is a very bad idea to mix aluminum alloys and stainless steels in any piece of equipment that may get wet; the result is rapid corrosion of the aluminum alloy. Where this must be done (as is often the case for aircraft) they frequently cadmium plate the stainless so that its galvanic potential more or less matches aluminum.

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General Guidelines: Use stainless steel for all cedar wood, ACQ lumber, decks and waterfront applications as well as for use in materials with a life expectancy of 30 years or more. All exterior projects should include either stainless steel or hot dipped galvanized fasteners for maximum protection against the elements. Aluminum and low-grade steel corrodes quickly in the presence of copper because of the difference in electro-chemical potential. All pressure treated lumber requires Hot Dipped Galvanized or Stainless Steel. 316 Stainless is superior to 304 and recommended for coastal and marine applications.

Where Do I use Stainless Steel in place of Hot-Dipped Galvanized?

For ACQ treated lumber in the presence of electrolytes, such as saltwater, copper reacts quickly with any metal close to it on the galvanic series of metals and alloys, causing corrosion. Since 304 grade stainless steel is closer to copper in the electro-motive series, corrosion is virtually nonexistent. For maximum long term corrosion protection, stainless steel is the only way to go!

Related Items:

• Fasteners
• Stainless Steel Fasteners