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.

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.

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.

Passivation agents, such as chromates, are sometimes applied to galvanized articles immediately after 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.

See also:
Wet Storage Stain Publication
Wet Storage Stain vs. White Rust Dr. Galv Article

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Comments

Dan Barlow

Hi Frank,

The galvanized steel may have already received a passivation treatment before leaving the galvanizing facility. This may have come in the form of a quench based post-treatment after the steel was galvanized. Contacting your galvanizer with this question will confirm whether or not this was done.

If not, you may consider asking for this conversion coating, or you may consider using a duplex system on the steel. The paint over the galvanized coating will act as a barrier and essentially passivate the underlying zinc.

frank yanchus

I have a customer who has just purchased a new upper condenser unit for his cooling tower system. All surfaces are galvanised steel. The manufacturer mentions in the users manual that we may “passivate” these surfaces before commissioning the unit. Do you have any suggestions as to how we could do that ? This unit is going to be mounted outside the plant, uncovered.

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