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Appearance Blemishes
Dross
Protrusions
Dross is the zinc/iron alloy by-product that forms in the galvanizing
kettle. Dross usually settles on the bottom of the kettle and, if stirred up
from the bottom, can attach to steel being galvanized. The galvanized
coating will commonly form around the dross particles, although rough
surfaces may result. This is not cause for rejection as the dross particles
are the same composition as the galvanized coating and only impair the
visual continuity of the surface. The corrosion protection is not
compromised by the presence of dross protrusions. |
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Flux
Inclusions
Zinc ammonium chloride, or “flux,” may adhere to steel being galvanized.
Flux inclusions are not cause for rejection, assuming the underlying coating
is sound and the flux deposits are removed. |
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Lumps
and Runs
Areas of thicker coating, sometimes resulting from fast withdrawal rates or lower zinc bath temperatures, are not detrimental to coating performance. ASTM standards require the zinc coating to be free of major imperfections. |
Zinc
Skimmings
Zinc skimmings are the oxide film that develops on the surface of the molten zinc. Zinc skimmings picked up from the surface of the bath during withdrawal have no detrimental effect on corrosion prevention performance and are not cause for rejection. |
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Gray
or Mottled Coating Appearance
Exposed zinc-iron alloy layers not
covered by a layer of free zinc result
in a matte gray or mottled coating. This
may happen over the entire coating or
in isolated areas. Steel chemistry contributes
to this occurrence. Because coating appearance
does not affect the corrosion prevention
provided, matte gray or mottled coatings
are not cause for rejection. |
Brown
Staining
If coatings with exposed intermetallic
layers (zinc-iron alloy layers) are exposed
to the environment, brown staining may
appear. This results from the interaction
between iron in the intermetallic layer
and the atmosphere. Coating performance
is not affected. |
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Rust
Staining
If galvanized coatings come into contact
with bare steel (such as chains used in
transportation, etc.), there may appear
to be rust staining on the galvanized
steel surface. This is actually a superficial
occurrence; the staining may be cleaned
off before end-use. |
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Wet Storage
Stain
The naturally-occurring formation
of a tenacious, abrasion-resistant zinc
carbonate patina provides yet another
component to the protection afforded by
galvanizing. The formation of this patina
depends on the galvanized steel being
exposed to freely-circulating air.
Stacking galvanized articles closely together for extended periods of time — thereby limiting access to freely-circulating air — can lead to the formation of a white, powdery product commonly called “wet storage stain.”
Wet storage stain is often superficial, despite the possible presence of a bulky, white product. In the vast majority of cases, wet storage stain does not indicate serious degradation of the zinc coating, nor does it necessarily imply any like reduction in expected service-life.
If wet storage stain does form, the affected objects should be arranged so that their surfaces dry rapidly. Once dry, most stains can be easily removed by brushing with a stiff, nylon bristle brush. If the affected area will not be fully exposed in service, or if it will be subjected to an extremely humid environment, even superficial white films should be removed with a stiff, nylon bristle brush.
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 Coating
Thickness
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