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Hot Dip Galvanizing of parts that trap water

March 15, 2012

Q. We are a structural steel manufacturer and as such do have many weldments HDG. We recently
fabricated some sump lids of grating with perforated steel welded to them. The HDG company tried to galvanize this sump cover and the zinc form the tank spewed all over as they tried to insert the sump lid into the zinc tank. They suggested that these sump lids could not be HDG because the water in the cleaning process was getting trapped in between the grating and the perforated metal plate. We have tried zinc electroplating and this is not a problem. We would prefer the HDG. Can you suggest anything?

Maurice Huet
- Alberta, Canada

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March 21, 2012

Most steel fabrications can be galvanized, but some need some design considerations or some fabrication technique to allow it.
After hanging (usually by disposable wires) the item must be capable to be lowered by crane into various liquids such that it does not trap any air, and raised such that it does not retain any liquids.
Often this is achieved by inserting vent and drain holes to allow air to escape and liquid to drain.

If liquids are retained, then when the item is lowered into zinc, the liquid turns to steam, sometimes violently, sometimes while submerged in molten zinc (450 degrees C), and then explosively.

But with consultation, most galvanizers will find a way to coat most steel.

Geoff Crowley
Crithwood Ltd.
Westfield, Scotland, UK