1.How to choose the type of galvanizing?
Increase the zinc layer thickness: This is one of the most direct and effective methods. Choose the minimum zinc layer thickness that meets or exceeds the "harsh environment" requirements in the relevant standards. Thicker zinc layer means more sacrificial protection.
Zinc-aluminum-magnesium coating: This is one of the most effective solutions to improve corrosion resistance. Adding aluminum and magnesium to zinc creates a coating with: A denser and more stable corrosion product layer (mainly composed of hydrozincite and zinc-magnesium hydroxide) that better blocks chloride ion and oxygen penetration. More uniform sacrificial anode protection. Excellent resistance to cut-edge corrosion and scratch corrosion. In coastal salt spray environments, its corrosion resistance is usually 2-10 times that of ordinary hot-dip galvanizing.
Galvalume: Aluminum provides excellent barrier protection (oxidation and chemical resistance) and zinc provides sacrificial protection. In coastal atmospheres, its resistance to red rust is worse than ordinary galvanizing, but its sacrificial protection is not as good as pure zinc or zinc aluminum magnesium, and its cut edge protection is poor. White rust resistance may not be as good as ordinary galvanizing.
High zinc aluminum alloy: The zinc content is higher than that of aluminum-zinc alloy, it has better sacrificial protection and good barrier protection, and its performance is between ordinary galvanizing and aluminum-zinc.
2.How to optimize the surface?
High-quality passivation:
Chromium-free passivation: The mainstream choice under environmental protection requirements. Choose a chromium-free passivation solution optimized for coastal environments (such as a composite system based on silane, titanium/zirconate, molybdate, phosphate, etc.). These passivation films can delay the formation of white rust and improve initial corrosion resistance.
Trivalent chromium passivation: The performance is better than hexavalent chromium passivation, more environmentally friendly, and has better corrosion resistance.
3.What role does protective coating play?
Organic sealer: A thin layer of transparent organic coating (such as water-based acrylic, polyurethane, epoxy resin, etc.) is applied on the passivation layer. This film can physically isolate the corrosive medium, significantly delay white rust and initial corrosion, and maintain beauty. This is a very cost-effective and commonly used method to improve coastal corrosion resistance.
Paint coating: For applications requiring a higher level of protection or a specific color, a complete paint system can be applied over the galvanized layer. Be sure to choose a primer that is compatible with the galvanized substrate (such as epoxy zinc-rich primer, epoxy zinc phosphate primer, or a dedicated galvanized layer primer), and then match it with a topcoat with good weather resistance (such as polyurethane, fluorocarbon paint). This provides double protection (sacrificial anode + barrier protection).
4.How can we improve the design and installation?
Avoid water accumulation: When designing, ensure that the components have good drainage slopes to avoid long-term accumulation of rainwater and condensation in grooves and gaps. Pay attention to drainage when drilling. ◦ Reduce gaps: Try to avoid the formation of narrow gaps (such as overlaps of steel plates), which are prone to form closed cells and accelerate corrosion. Use sealants to fill necessary gaps. ◦ Avoid contact between dissimilar metals: If galvanized steel must be connected to metals with more positive potential (such as stainless steel and copper), it must be strictly electrically isolated using insulating gaskets or sleeves, otherwise it will cause severe galvanic corrosion. ◦ Ventilation: Ensure good ventilation inside the structure to reduce humidity and accelerate surface drying. ◦ Protect cut edges and drilled holes: These areas have the thinnest zinc layer or are damaged. They can be carefully repaired with zinc-rich paint (cold galvanizing paint) to provide additional sacrificial protection.
5.What other measures can be taken to improve it?
Sacrificial anode: For critical or difficult to maintain components (such as dock pile foundations, underwater structures), a metal with a more negative potential (such as zinc alloy or aluminum alloy anode blocks) can be attached to the galvanized steel structure to provide additional current protection.
Impressed current cathodic protection: Usually used for large or buried/underwater structures, the protection current is provided by an external power supply. It is less used in coastal atmospheric environments.