The process begins with the removal of mill scale, a thin layer of iron oxide that forms during the steel rolling process.

1. Removal of Mill Scale:

• Weathering: Using wire brushes.
• Pickling: Immersing plates in a weak solution of H₂SO₄ or HCl.
• Shot Blasting: Abrasive blasting to remove rust and mill scale.
• Flame Cleaning: Heating and cleaning the surface.

Freshwater Washing and Drying: Ensures the surface is clean and ready for priming.

2. A primer is then applied. This acts as a base layer for subsequent coatings and improves adhesion. Common types include epoxy primers with corrosion-inhibiting pigments like iron oxide, zinc, and calcium phosphates (though zinc content is reduced due to safety concerns).

3. Next comes the anticorrosive coating, the main layer offering corrosion protection. Common choices are two-component epoxies, coal tar epoxies, and epoxy or polyester coatings with glass flakes for added strength and water impermeability.

4. Finally, an antifouling coating prevents marine organism attachment. While tin-based paints were once common, environmental regulations have led to their replacement with copper-based, silicone-based, or non-TBT (Tributyltin) self-polishing coatings. These utilize seawater-soluble polymers. The number of antifouling layers (two or three) depends on the chosen system and desired lifespan. The dry film thickness (DFT) of the primer is closely monitored to prevent cracking and ensure effective protection.

Corrosion prevention begins at the design stage:

• Avoid dissimilar metal joining to minimize galvanic corrosion.
• Use high-quality steel plates based on the galvanic series.
• Minimize areas where water can accumulate by ensuring proper drainage systems.
• Ensure sufficient anodes are installed in optimal positions.
• Consider installing Impressed Current Cathodic Protection (ICCP) and Marine Growth Prevention Systems (MGPS).

Maintenance:

• Regular checks and maintenance of ICCP and MGPS systems.
• Renewal of sacrificial anodes during dry-docking.
• Cleaning, repairing, and repainting surfaces to maintain the protective coatings.
• Ensuring proper drainage and inspecting for any areas of corrosion.

Sacrificial anodes are less noble metals (more electro-negative) than the hull material. When immersed in seawater, they corrode preferentially, protecting the hull. Common materials include zinc, aluminium, and magnesium. They are welded to the hull for good electrical contact.

• External surface: Large anodes provide complete protection until the next dry-docking.
• Internal surface: Anodes are fitted inside tanks, filters, and coolers to prevent internal corrosion.
• MGPS: These systems utilize sacrificial anodes to protect seawater lines and pumps, further preventing marine growth.
• ICCP: Impressed current systems offer an alternative, using an external DC power source and permanent anodes (typically titanium or platinum) for continuous protection. These systems are self-regulating and adjust current output based on hull coating condition. Regular monitoring (e.g., monthly data analysis) is important for both sacrificial and impressed current systems.