Marine Hull Sequence
Surface preparation in shipyards is governed by the harsh saline environment. To prevent "under-film" corrosion, the blasting sequence must achieve surgical cleanliness while managing chloride levels.
1. High-Pressure Wash
Removal of marine growth and salt deposits before blasting to prevent driving chlorides into the steel pores.
2. Sa 2.5 Technical Blasting
Using Garnet or Copper Slag to achieve a near-white metal finish with an anchor profile of 75-100 microns for heavy marine epoxies.
3. Dust Extraction & Verification
Immediate removal of spent abrasive and dust to allow for surface profile and chloride testing prior to primer application.
Ballast Tank Logic
Confined space blasting requires high-CFM ventilation and mandatory Grade D Breathing Air. Steel Grit or Garnet is preferred here to minimize dust levels and ensure Sa 3.0 white-metal cleanliness for long-life tank linings.
The Chloride Threat
Coastal humidity causes rapid "flash-rusting." Technical shipyard operators utilize high-capacity Moisture Separators to ensure dry air, preventing media clogs and ensuring the abrasive hits the steel with zero moisture-bound salts.
Coating Verification Sequence
- Profile Check: Using Profile Gauges to confirm mechanical bond prep.
- DFT Verification: Multi-point Digital DFT checks after each coating layer.
- Holiday Testing: Final high-voltage spark check for 100% lining continuity.
Frequently Asked Questions
What surface standard applies to ship hull and topside blasting?
Ship hull external: Sa2.5 (Near-White Metal) per ISO 8501-1 for antifouling and hull coatings per IMO MARPOL. Topside and superstructure: Sa2 minimum for maintenance repaints, Sa2.5 for newbuild. Ballast tank: Sa2.5 per IMO Resolution A.1049(27). Profile: 30-75µm Rz depending on coating system (Epoxy: 30-50µm, Vinylation: 50-75µm).
What environmental controls apply to shipyard blasting?
Marine environmental controls: (1) Containment sheets mandatory — no abrasive or paint debris into water. (2) DfT/MARPOL compliance — no harmful substances to sea. (3) SSPC SP10/NACE 2 for all marine coatings. (4) Abrasive recovery and disposal — copper slag classified as non-hazardous (EPA 40 CFR 261). Grit contaminated with heavy metals requires special disposal per RCRA.
Can wet blasting be used in shipyard operations?
Yes — wet blasting (vapor/slurry) is preferred for: underwater hull cleaning (no diver risk), environmentally sensitive areas, and areas with hydrocarbon risk. Wet blasting achieves Sa2.5 but the surface is wet — use W1 designation per ISO 8501-2. After wet blasting: surface must dry or be treated with rust-preventive wash before coating. Flash rust prevention is critical in marine environments.