Why Do Galvanized Products with Powder Coating Rust Quickly Near the Sea?

Galvanized products that are powder-coated are designed to resist corrosion and provide long-lasting durability. However, in coastal environments, these products can sometimes rust prematurely. If you’re located near the sea, understanding why this happens and how to prevent it can save you both time and money. Let’s explore the key reasons behind this issue and what can be done to address it.


1. The Harsh Coastal Environment


Coastal areas present unique challenges for metal products:


Salt Spray and High Humidity:
  •  The air near the sea contains high levels of salt and moisture. Salt particles are highly corrosive and can penetrate even small imperfections in the powder coating.
  • Humidity accelerates the formation of rust by providing the moisture needed for corrosion to occur.


Constant Exposure:

Products near the sea are often exposed to wind-borne salt spray and fluctuating temperatures, which can weaken protective coatings over time.


2. Common Issues with Galvanizing and Powder Coating


Even though galvanizing and powder coating are robust protective measures, improper application or compatibility issues can compromise their effectiveness:

  • Poor Surface Preparation

Before applying powder coating, the galvanized surface must be properly cleaned and pre-treated. If this step is skipped or poorly done, contaminants or residues can prevent the coating from adhering properly, leading to weak spots.


  • Incomplete Curing of Powder Coating

Powder coatings must be cured at precise temperatures for the right amount of time. If this process is not followed correctly, the coating may form a weak bond, making it prone to cracking and peeling.


  • Porosity in the Coating

Small pores in the powder coating can allow salt and moisture to seep through, reaching the galvanized layer underneath and starting the rusting process.


  • Damage to the Galvanized Layer

The zinc coating in galvanized products acts as a sacrificial barrier to protect the steel. If this layer is damaged during handling or application, its ability to prevent rusting is compromised.


  • Lack of Synergy in the Duplex System

When galvanizing and powder coating are combined, the two layers must work together as a duplex system. If the powder coating is too rigid or poorly bonded, it can crack, exposing the zinc layer to the environment.


3. Why Rusting Is Worse Near the Sea


  • Chloride Attack:

 ​Salt in the air contains chloride ions, which aggressively attack both the powder coating and the galvanized layer, especially if there are scratches or pinholes in the coating.


  • Breakdown of the Zinc Patina:

 Zinc in the galvanizing layer normally forms a protective patina that slows down corrosion. However, in saline environments, this patina breaks down faster, exposing the steel underneath to rust.


4. How to Prevent Rusting Near the Sea


If you’re manufacturing or installing galvanized and powder-coated products near the sea, follow these steps to improve their durability:


  • Improved Surface Preparation

Ensure the galvanized surface is thoroughly cleaned, degreased, and pre-treated (e.g., using zinc phosphate or chromate conversion) before applying the powder coating.


  • High-Quality Powder Coating
    • Use marine-grade or corrosion-resistant powder coatings specifically formulated for coastal environments.
    • Apply a thicker powder coating layer to provide extra protection against salt and moisture.


  • Sealing and Inspection
    • Add a sealing topcoat over the powder coating for enhanced durability.
    • Inspect for defects such as pinholes, cracks, or peeling, and repair them promptly.


Duplex System Optimization
    • Use a galvanizing process that ensures a thick, uniform zinc layer.
    • Work with powder coating specialists who have experience with galvanized products and understand coastal requirements.


Regular Maintenance
    • Wash powder-coated surfaces regularly with fresh water to remove salt deposits.
    • Apply corrosion inhibitors to protect exposed metal if needed.
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