Surface anti-corrosion treatment for CCS Grade D shipbuilding steel plates

1. Surface Pre-treatment of Steel Plates

1.1 Surface Rust Removal

A shot blasting process is employed to remove scale, rust and impurities from the surface of CCS Grade D shipbuilding steel plates. The rust removal grade must meet the Sa2.5 standard specified by the marine industry, and surface roughness must be controlled within the range of 40–75 μm to enhance coating adhesion.

1.2 Degreasing and Cleaning

The steel plate surface is wiped with an organic solvent to remove rolling oil and machining grease, preventing the oil film from reducing the adhesion of the anti-corrosion coating and avoiding flaking and blistering of the coating in the marine environment.

2. Application of Anti-Corrosion Coating

2.1 Primer Coat

A zinc-rich epoxy primer is applied, with a dry film thickness of 60–80 μm. Zinc powder provides sacrificial anode protection, inhibiting electrochemical corrosion of the steel substrate, and is suitable for hull plating exposed to seawater.

2.2 Intermediate Coat

Apply an epoxy micaceous iron oxide intermediate coat with a thickness of 100–120 μm to improve coating density, enhance barrier properties against moisture and salt spray, and improve the overall permeability resistance of the coating system.

2.3 Topcoat

A marine-grade polyurethane topcoat is selected, with a thickness of 50–60 μm. It offers excellent weather resistance and anti-fouling properties, resisting UV radiation and marine biofouling, maintaining a smooth hull surface and reducing navigational drag.

3. Specialised Corrosion Protection for Critical Areas

3.1 Ballast Tank Steel Plating

Heavy-duty epoxy anti-corrosion coatings and cathodic protection technology are employed to withstand the alternating wet and dry conditions of the marine environment.

3.2 Deck Structures

Increase the coating thickness and incorporate anti-slip abrasive particles to resist mechanical wear and rain erosion.

3.3 Hulls in Cold-Water Regions

Select low-temperature-resistant anti-corrosion coatings to prevent cracking caused by temperature fluctuations.

4. Anti-Corrosion Maintenance Cycle

Following standardised anti-corrosion treatment, the effective service life of a CCS Grade D steel hull can reach 8–12 years. It is recommended that surface coating inspections be carried out every two years, with localised repairs to areas of flaking and corrosion to extend service life.

5. Conclusion

Anti-corrosion treatment directly affects the service life of CCS Grade D shipbuilding steel plates in marine environments. A scientific rust removal process combined with a three-layer coating system can effectively resist seawater corrosion. Targeted anti-corrosion schemes should be formulated based on the specific conditions of the navigation waters to maximise structural stability.