Understanding White Rust
Nature, Prevention, and Maintenance
White rust is a term that refers to a form of superficial corrosion that manifests on zinc coatings when subjected to moisture
This is especially extreme in environments with high humidity, such as coastal areas or during prolonged exposure to rain and other elements. This corrosion appears as a chalky, white powdery substance on the surface of zinc-coated items, which can lead to concerns about the integrity of the coating.
The Nature of Zinc Coating
When freshly applied, a zinc coating possesses a bright, shiny silver appearance. This dynamic quality indicates that the zinc layer is still in the process of establishing its protective barrier. As time progresses, the zinc coating undergoes a transformation characterized by the gradual accumulation of a zinc carbonate film. Eventually, this results in the development of a dense, insoluble, and dull grey film, which indicates that the zinc surface has stabilized adequately.
Importantly, the presence of white rust should not be mistaken for a defect or an inferior quality of the zinc coating. Rather, it is a natural response to environmental factors, specifically related to moisture exposure. Newly galvanized items are particularly vulnerable to the formation of white rust during the initial stages of their lifecycle, as the protective coating is still settling and has not yet reached its full effectiveness.
Prevention Strategies
To mitigate the risk of white rust, it’s critical to implement proper storage and maintenance practices for newly coated zinc items. These measures can significantly enhance the longevity of the coating:
- Immediate Care Post-Galvanizing: Newly coated items should be stored in a dry, well-ventilated environment to allow the zinc layer to cure adequately without premature exposure to moisture.
- Regular Inspections: Conduct frequent checks of zinc coatings, particularly for items exposed to moist conditions. This is especially important for steel items located in areas with consistent humidity, which can accelerate corrosion processes.
- Proper Cleaning: If white rust is detected, it is essential to remove it promptly using a wire brush. This helps to prevent further corrosion and allows for a more thorough inspection of the coating’s integrity.
- Coating Thickness Assessment: After cleaning, it’s imperative to check the thickness of the zinc coating to ascertain that it remains intact and has not been compromised by corrosion or wear.
- Avoiding Red Rust Development: Neglecting to address white rust promptly may lead to more severe corrosion in the form of red rust, which can threaten the structural integrity of the underlying steel.
Tips for Specific Applications
Larger structural items should be brushed clean whenever feasible. For smaller items like boat trailers, which are frequently exposed to saltwater, rinsing with fresh water after use is crucial. Additionally, when parking these items, position them in a way that allows any remaining water to drain efficiently, facilitating proper drying.
Long-Term Considerations
Always ensure that the zinc coating is allowed adequate time to stabilize before putting the items into active service. This precaution helps maximize the effectiveness of the zinc as a protective barrier and minimizes the risk of corrosion-related issues in the future.
By understanding the nature of white rust and implementing effective preventive measures, the longevity and performance of zinc-coated items can be significantly enhanced, safeguarding them from the adverse effects of environmental exposure.
Durban Galvanizing’s facilities allow for the dipping of large fabricated steel items, our Phoenix branch boasts a Zink kettle 14m long. Our team of technical experts are available to provide advice and guidance to ensure your steel items are coated to the highest standards and ensure years of uninterrupted service.