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Hot Dip Galvanize Versus B633 Zinc Plate
What data is available that describes the level of protection from rust of "hot dip galvanize" versus the different types and service conditions of ASTM B633 [affil. link to spec at Techstreet] zinc plating? My company produces OEM equipment, some of which is used in outdoor environments. My fabrication vendors tell me they have been allowed to substitute "zinc plate" for a hot dip galvanized coating because of lead time delay from this region's one remaining hot dip galvanizer. I sympathize with them but know I'm not getting the effective protection I should be providing. I know the yellow chromate conversion provides better protection than as-plated or colorless conversion coating but suspect I'm getting much less protection when I continue to allow this substitution.
Can anyone recommend any articles or reports?
- Minneapolis, Minnesota
The corrosion resistance of zinc is directly proportional to its thickness. The actually undefined term "Commercial zinc plating" usually means about .0002" of zinc plating. The heaviest zinc electroplating you are likely to see is about .0006". Compare these to the specified galvanizing thickness and, yes, you will see a much lower anticipated life. A better alternative might be "mechanical plating"
Ted Mooney, P.E.
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