Introduction to Marine Anti-Corrosion Coatings

I. Composition of Ship Anti-Corrosion Paints:

Anti-corrosion paints come in a wide variety and are generally classified by composition into: epoxy anti-corrosion paint, polyurethane anti-corrosion paint, acrylic anti-corrosion paint, and Chlorinated Rubber anti-corrosion paint.

II. Key Characteristics and Applications of Marine Anti-Corrosion Paints:

These coatings perform reliably under harsh conditions, offering excellent durability and weather resistance. They maintain effectiveness for 10 to 15 years or more in marine and underground environments, and can withstand exposure to acidic, alkaline, saline, and solvent media for over 5 years under specified temperature conditions.

III. Application Guidelines for Marine Anti-Corrosion Paints:

1. Surface Preparation
• Remove impurities, oil, grease, and deposits from the surface using cleaning methods specified in SY/T0407 “Specification for Surface Preparation of Steel Before Painting.”
• Perform blast cleaning on steel surfaces according to SY/T0407 methods. Proceed in the sequence: ceiling, walls, then floor. Rust removal quality must achieve Sa2.5 grade as defined in GB/T8923—1998 “Rust Grading and Blasting Grading for Steel Surfaces Before Painting.” Anchor pattern depth should be selected based on the required corrosion protection level; for standard applications: approximately 40μm. Use a 6-8 mm nozzle with inlet compressed air pressure of 0.5-0.6 MPa. Maintain a blasting angle of 30-75°, an impact distance of 100-200 mm, and abrasive particle size of 0.8-4 mm. When sandblasting thin steel plates, reduce abrasive particle size and air pressure appropriately. Nozzles must be discarded when wear at the outlet end exceeds half the original inner diameter. Surface pretreatment for attachments must match that of the main component.
• After blasting, surfaces must be thoroughly cleaned with dry, clean, oil-free compressed air.
• Any defects exposed on steel surfaces or welds after blast cleaning must be addressed.
• Safety measures: Maintain ventilation to keep solvent gas concentrations below hazardous levels. Operators must wear protective clothing and masks. Ground the blast hose.

2. Paint Preparation
• If the anti-corrosion paint is a two-component coating, mix the components only immediately before application. Before mixing, verify that Components A and B are compatible, match the required application grade, and have not expired.
• Before mixing Components A and B, stir thoroughly until no sediment remains at the bottom and the mixture is uniformly blended.
• Prepare a small test batch using the mixed A and B components in the specified ratio. Adjust viscosity with the designated thinner to optimize application conditions, ensuring consistent film thickness and quality.
• Calculate the required quantities of A and B components based on the application area and desired film thickness. Ensure the mixed batch is used within 6 hours to prevent excessive curing and thickening, which compromises film quality.
• Control the amount of dedicated paint thinner to no more than 15% (for spraying) or 8% (for brushing) of the total weight. Add it to Component A at the calculated ratio and mix thoroughly. Then add Component B and stir for 10-15 minutes to cure the mixture. Finally, let it stand for 15-20 minutes to eliminate air bubbles introduced during mixing. The duration of mixing and standing depends on the batch size.
• Strain the mixed coating through a 100-mesh filter before spraying. If the coating thickens excessively due to over-reaction during spraying, stop immediately. Discard the mixture and prepare a new batch. Over-reaction time varies with ambient temperature: shorter times at higher temperatures require smaller batches, while longer times at lower temperatures warrant larger batches.

3. Application Process
• Specific application procedures and quality assurance measures for the protective coating shall be developed based on the structure of the item being coated.
• Environmental conditions during application must comply with the manufacturer's specifications. Outdoor coating operations shall cease during rain, snow, fog, sandstorms, or similar weather conditions. Application is not recommended when ambient temperatures fall below -5°C or exceed 40°C, or when relative humidity exceeds 80%. Prevent rainwater immersion of uncured coatings.
• If rusting occurs between surface pretreatment approval and application of the first primer coat, re-pretreat the rusted areas before coating. For large vessels where sandblasting cannot be completed within one day, seal them to prevent air convection and prolong rust reappearance time.
• Chlorosulfonated polyethylene anti-corrosion paint may be applied using airless spraying, air spraying, brushing, or rolling. Application should proceed from top to bottom, ensuring uniform coverage without missed areas. The specific application method shall be determined according to the anti-corrosion construction plan. Application operations shall comply with the following provisions:
A. When spraying, maintain a uniform gun movement speed and keep the nozzle perpendicular to the surface.
B. When brushing, apply even pressure in a consistent direction to prevent surface fuzziness.
C. When using a roller, ensure the roller is evenly coated with paint without excessive loading. Apply even pressure without excessive force, maintaining a consistent speed. Roll in the same direction for each pass, though the direction may vary between passes. Use brushes to apply paint to edges, fittings, and other areas inaccessible to the roller.
• Apply additional paint or increase the number of coats on weld seams, edges, corners, and uneven surfaces.
• The interval between each coat should not exceed 24 hours. Apply the next coat after the previous coat has reached surface dryness. If the previous coat has cured, roughen the surface before applying the next coat. After the final topcoat application, allow at least 7 days of curing at ambient temperature (25°C) before use. If curing temperature is below 10°C, cure for at least 10 days before use.
• During application, measure wet film thickness at various locations and promptly adjust coating viscosity and application parameters to ensure the final protective layer thickness meets design requirements.