Proper Storage & Handling
It is important to properly store and transport galvanized steel so as not to disrupt the development of the zinc patina. Zinc, like all metals, begins to corrode naturally when exposed to the atmosphere. However, zinc corrosion products actually form a tenacious, abrasion-resistant patina which helps to provide hot-dip galvanizing with its long service life. The formation of this patina depends on the galvanized coating being exposed to freely circulating air. Stacking galvanized articles closely together, or nesting, for extended periods of time, thereby limiting access to freely circulating air, can lead to the formation of a white powdery product know as wet storage stain.
Wet Storage Stain
Wet storage stain is essentially a buildup of zinc hydroxide on the surface of the steel. If not allowed to dry, this build up will remain on the steel and if it accumulates in mass quantities can cause excessive corrosion. Mild to medium buildup of wet storage stain is not reason for concern as it will weather away when the parts are put in service. However, heavy buildup may require using a nylon bristle brush and/or solvent cleaners to remove it.
Minimizing Wet Storage Stain:
- Provide adequate ventilation between stacked pieces and avoid nested stacking
- Elevate and separate articles stacked outdoors with strip spacers (poplar, ash, spruce); and during shipping if there is the likelihood of condensation
- Incline parts to allow for maximum drainage
- Prevent uncovered material from being left at in-transit loading points where it may be exposed to rain, mist, condensation, or snow
- Thoroughly dry small items that are quenched and stored in containers and include a dehumidifying agent in the sealed containers
- Store galvanized material under cover in dry, well-ventilated conditions, away from doorways open to the environment
- Treat with passivating agent
- Maintain a low humidity environment
Wet storage staining 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 likely reduction in the products service life. If wet storage stain does form, the objects should be arranged so that their surfaces dry rapidly. Once dry, most stains can be easily removed by brushing with a stiff bristle (not wire) brush. If the affected area will not be fully exposed in service, or if it will be subject to an extremely humid environment, even superficial white films should be removed with a stiff bristle brush. This allows for the successful formation of galvanized coatings protective zinc carbonate patina.