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Wet Storage Stain American Galvanizers Association

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11/20/2020
Wet Storage Stain | American Galvanizers Association
» Wet Storage Stain
Wet Storage Stain
January 14, 2010
Authored by Dr. Tom Langill
Wet storage stain is the bulky white or gray deposit formed by accelerated corrosion of the zinc coating when closely
packed, newly galvanized articles are stored or shipped under damp and poorly ventilated conditions. Weathered zinc
surfaces which have already formed their normal protective layer of zinc corrosion products are seldom attacked. Wet
storage stain is found most o en on stacked and bundled items, such as galvanized sheets, plates, angles, bars, and
pipe.
The extent of the damage caused by wet storage stain depends on the duration of exposure to retained moisture with
little airflow over the galvanized coating. In the vast majority of cases, wet storage stain is light and does not necessarily
imply any likely reduction in the expected life of the product. However, medium and heavy build-up can cause extreme
damage to the coating when le untreated and may require stripping and regalvanizing. Examples can be seen below.
Prevention of wet storage
stain includes not tightly stacking
newly galvanized products on top of
one another, removing standing
water, and providing adequate air
flow over the zinc surfaces.
Example of Light Wet Storage Stain
Example of Medium Wet Storage Stain
Newly galvanized articles should
be stored under cover in dry and well
ventilated areas. If outdoor stacking
is unavoidable, the articles should be
raised from the ground and separated
with strip spacers to provide free access
of air to all parts of the surface. They
also should be inclined in a manner
which will give maximum drainage.
Galvanized steel should not be stored
on wet soil or decaying vegetation.
Example of Heavy Wet Storage Stain
The use of spacers is recommended
during any shipping if there is a
likelihood of condensation. It is
important that resinous wood not be used for spacers or packing, since the resin itself can start corrosion. Woods used
in transporting should be dry and untreated with preservatives or fire retardant chemicals. Poplar and spruce have been
used with good results. Untreated wood cannot be transported across the United States/Canada border.
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Wet Storage Stain | American Galvanizers Association
Passivation agents, such as chromates, are sometimes applied to galvanized articles immediately a er galvanizing to
prevent wet storage stain. Other passivation agents such as clear coats and oils have also been used to prevent wet
storage stain. Proper storage of galvanized steel is necessary even when passivation agents are used.
White rust can occur on unpassivated cooling towers in service in water with a pH level above 8.2 or 8.3. If the cooling
towers cannot be chromate quenched, the solution is to use a phosphate treatment and operate the tower at a pH no
higher than 7.8 for a few months, then return to normal operating levels.
See also: Wet Storage Stain Publication
Wet Storage Stain vs. White Rust Dr. Galv Article
© 2020 American Galvanizers Association. The material provided herein has been developed to provide accurate and
authoritative information about a er-fabrication hot-dip galvanized steel. This material provides general information
only and is not intended as a substitute for competent professional examination and verification as to suitability and
applicability. The information provided herein is not intended as a representation or warranty on the part of the AGA.
Anyone making use of this information assumes all liability arising from such use.
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