Storage stain is a white corrosion-formed stain which appears on the surface of galvanized steel products. Though its appearance is normally white, it can also be grey or black. Storage stain occurs when the galvanized steel product is tightly wrapped and overlapped upon itself and gets wet from rain or condensation in the air. This causes the corrosion products like zinc to emit a white substance when it comes in contact with moisture. The phenomenon is often referred to as “white rust.” While white rust is unsightly, white rust is not harmful to your galvanized steel. Here are a couple of ways you can prevent it from occurring.
Chemical Passivating Treatments. This is the best way for you to prevent white rust on your galvanized steel products both during shipment and while your structure is standing. The treatment is applied by the steel manufacturer and is done by applying a thin protective coating during the galvanization process. Clear passivation coatings have been proven to be very effective over the years in minimizing storage stain. It is important to note, though, that this process does not prevent storage stain. If the steel product is coiled, gets wet, and sits in a warehouse for some time, storage stain will still occur.
Passivating Oils. You may choose to use rust inhibiting oils on your galvanized steel. The oils contain chemicals which are called corrosion inhibitors. Inhibitors are what protect your steel from the elements and the oil is merely a carrier for the inhibitor. To apply, the most common method is through an electrostatic applicator. The oils themselves are not intended for lubrication and should not be used as such. Another type of oil called “vanishing oil” is also used. In this case, the oil evaporates when exposed to air, leaving behind the inhibitor.