White Rust What Happens ?
Galvanized materials in the stack are formed of zinc compounds called white rust which causes water to enter between them or humidity due to ambient conditions. White rust does not mean that the galvanized quality is low. Parameter storage and environmental conditions are important for the formation of white rust.
White rust; The zinc coating on the surfaces of galvanized coated steel and sheet surfaces exposed to damp conditions and inadequate ventilation conditions undergo rapid corrosion and show itself as white or gray mold deposits. It is usually caused by shipping conditions or unfavorable storage conditions in the premises. This problem is more frequently encountered on surfaces that are stacked with no space between them.
A very reactive element, zinc oxide, rapidly forms a layer of zinc oxide on the surface of the air-bearing surface. The formation of this thin and rigid layer is the first step in the development of protective corrosion film in galvanized coatings. The reaction of this surface with rain or moisture in an open environment results in a corrosion product in the form of zinc hydroxide in a porous and gelatinous form. During drying, this product reacts with carbon dioxide in the atmosphere and is converted mainly into zinc carbonate (2ZnCO3.3Zn (OH) 2). After a certain time, this white-gray inter-color appearance occurs. Zinc carbonate, formed on the galvanized surface, is the main mechanism preventing white rust formation.
Dampness of surfaces during storage or stacking, direct contact with rain or sea water, chilling due to atmospheric or temperature changes, white rust formation. The packing process, which is tightly done in humid and hot environments, requires that the noodle is kept inside and that the drying process is not carried out; Thus causing white rust formation. In fact, the most important reason for white rust is water itself.
In galvanized products, the formation of white rust can be reduced or completely avoided by reducing the ambient humidity to the non-condensing levels. The necessary ventilation conditions must be provided or heated to a temperature that will prevent condensation of the air in the air. The relative humidity of the stock should not exceed 75%. If adequate ventilation is not provided in stock areas, galvanized materials should be stocked in a separate place where ideal conditions can be established.
What are the measures to prevent the formation of white rust ?
In galvanized products, the formation of white rust can be reduced or completely avoided by reducing the ambient humidity to the non-condensing levels. The necessary ventilation conditions must be provided or heated to a temperature that will prevent condensation of the moisture in the stored air. The relative humidity of the stock should not exceed 75%. If adequate ventilation is not provided in stock areas, galvanized materials should be stocked in a separate place where ideal conditions can be established.
To avoid excessive condensation of air in storage areas, especially in winter, the daytime temperature difference should be maximum 10 ° C.
Galvanized materials should not be stalled for a long time; For this reason, customers should be warned that the waiting period should not exceed 2 months after the customer has been warned about the waiting conditions. The water or humid air entering the package during loading and transportation will be imprisoned and shortly cause white rust. This phenomenon is one of the most important factors in the formation of white rust.
Materials must not get wet during transportation. The vehicle must be completely covered with dry and sturdy canvas. Transport of galvanized products shall not be allowed with untransferable transport means.
Galvanized materials must never be left in an open space atmospheres, protected from rain, water and humidity by being stored in a closed and ventilated environment. Generally, in areas exposed to excessive rainfall, white rust comes to the foreground in exposed materials. There is a frequent problem with materials stacked on top of each other. A thin white rust layer forms on the surface. Light rust has no effect on coating quality.
White Rust Cleaning:
Since corrosion is a natural phenomenon, it is not possible to erase it entirely from the earth. However, the detrimental effect of corrosion can be reduced or controlled.
All white rust layer is cleaned using a wire brush. By measuring the coating thickness it will be seen that the zinc coating in this area is preserved. Storage of the materials in a dry environment should be ensured.