During storage, transportation, and use, electrogalvanized steel strips are often susceptible to white rust corrosion due to environmental factors. This corrosion not only affects the product's appearance but can also reduce its corrosion resistance. White rust formation is essentially an electrochemical corrosion process. When condensation on the zinc plating surface comes into contact with gases such as oxygen and carbon dioxide in the air, a corrosive electrolyte is formed. This creates an oxygen concentration cell on the zinc surface, causing rapid local dissolution of the zinc layer and generating white zinc hydroxide corrosion products. If the ambient humidity is high or corrosive gases are present, the corrosion products will further transform into basic zinc carbonate. However, if air circulation is poor, the zinc hydroxide cannot be completely converted, ultimately forming a loose white rust layer. Therefore, preventing white rust formation through process control requires a comprehensive protective system that addresses multiple aspects, including plating treatment, storage environment, and packaging methods.
After the electrogalvanized steel strip is manufactured, surface treatment is the first line of defense against white rust. Passivation treatment, by forming a dense chemical conversion film on the plating surface, can significantly improve its corrosion resistance. Traditional chromate passivation is gradually being replaced by chromium-free passivation, such as titanate, silicate, or organic passivation processes, due to environmental concerns. These technologies can generate a stable and strongly adhering protective film on the coating surface, effectively isolating moisture and corrosive gases. In addition, oiling is also a common method; applying a thin layer of anti-rust oil to the coating surface forms a physical barrier, delaying moisture penetration. For high-end applications, composite coating technologies, such as epoxy resin or polyurethane coatings, can be used to further enhance protective capabilities.
Humidity control in the storage environment is crucial to preventing white rust. Electrogalvanized steel strips should be stored in dry, well-ventilated warehouses, avoiding direct contact with the ground or damp walls to reduce condensation. If outdoor storage is necessary, the steel strips should be elevated using wooden supports and covered with waterproof tarpaulins, ensuring the supports are dry and untreated to prevent chemical penetration. Dehumidification equipment can be installed in the warehouse to control relative humidity within a reasonable range, especially during the rainy season or in areas with high temperature and humidity, requiring enhanced environmental monitoring and control. In addition, appropriate spacing should be maintained when stacking steel strips to avoid obstructing airflow and promoting moisture evaporation.
Optimizing packaging methods is equally important. During transportation, if the packaging is not properly sealed, temperature differences can cause condensation to accumulate inside, leading to white rust. Therefore, moisture-proof packaging materials, such as vapor phase corrosion inhibitors or plastic films, should be used, and desiccants should be placed inside the packaging to absorb residual moisture. For steel strips exported by sea, special attention must be paid to humidity control within the container. Container desiccant bars or desiccant boxes can be installed, while avoiding direct contact between the steel strips and the container walls to prevent salt spray corrosion. Furthermore, the surface of the steel strips should be ensured to be dry before packaging to prevent residual moisture from being trapped inside.
Protection during transportation needs to be tailored to the specific transportation method and route. For land transportation, prolonged exposure to rain and snow should be avoided. If traversing damp areas, additional protection for the steel strips should be provided in advance, such as adding layers of packaging or using waterproof covers. In addition to the aforementioned packaging optimizations, it is crucial to monitor temperature and humidity changes during sea transport. Direct shipping routes should be prioritized to minimize transshipment and reduce the risk of cargo exposure at ports. Furthermore, the cleanliness of the transport vehicles is essential to prevent contact between the steel strip and corrosive substances.
Process parameter control during production directly impacts coating quality. During electroplating, current density, temperature, and plating solution composition must be strictly controlled to ensure a uniform, dense coating free of defects such as pores or cracks. Defects in the coating allow moisture and corrosive gases to easily penetrate the substrate, accelerating white rust formation. Post-processing steps such as washing and drying must be performed according to regulations to prevent residual plating solution or moisture from causing localized corrosion. For example, incomplete washing may leave residual chloride ions on the coating surface, leading to pitting corrosion in humid environments.
Regular inspection and maintenance are necessary to ensure the continued effectiveness of protective measures. Companies should establish a comprehensive inspection system and regularly conduct visual inspections of stored steel strips, focusing on the presence of white rust or signs of corrosion. For steel strips that have developed slight white rust, they must be cleaned and re-protected promptly to prevent further corrosion. Simultaneously, the storage environment, packaging materials, and transportation vehicles must be regularly assessed, and aging or malfunctioning protective equipment must be replaced in a timely manner to ensure the reliability of the entire protective system.
