When seawater is constantly trying to eat your steel
Carbon steel in seawater corrodes at roughly 0.1 mm per year — and that's before you account for chlorides, biofouling, mechanical wear from waves, or the pH swings of splash-zone exposure. Conventional paint systems can manage this for years, but they don't last decades. Thermal Spray Aluminium (TSA) does — by combining a sacrificial cathodic mechanism (pure aluminium gives up electrons before steel does) with a thick barrier layer.
We deploy TSA via twin-wire arc spray onto blast-cleaned steel. Coating thickness 200-500 µm is typical, with optional sealer or topcoat depending on the service.
Where we recommend TSA
- Offshore platform topsides in splash and atmospheric zones
- Riser pipe protection in seawater-immersed and tidal zones
- Subsea structures including jacket members, conductors, J-tubes
- Seawater intake / outfall pipework for desalination and power plants
- Ship structures and ballast tank externals
- Bridge components in coastal or marine environments
- High-temperature carbon steel in oil & gas service (TSA prevents sulfidation up to 600 °C)
How TSA works
Pure aluminium wire is fed into a high-velocity arc-spray gun where it's atomized and propelled onto the steel substrate at supersonic speed. The molten aluminium particles flatten and bond mechanically + metallurgically to the blasted steel, forming a 200-500 µm porous-but-coherent metal layer.
The aluminium then does two jobs:
Cathodic protection. Aluminium has a more negative electrode potential than steel — so any chloride or moisture that penetrates the porous coating finds aluminium to corrode preferentially, sparing the steel.
Barrier. Once the aluminium starts to corrode (from the surface in), it forms a passive aluminium oxide layer that further slows the corrosion process. This layer self-heals when scratched.
Build properties
| Property | Value |
|---|---|
| Coating thickness | 200-500 µm (project-spec dependent) |
| Bond strength | ≥ 7 MPa (per ISO 4624) |
| Service temperature | up to 540 °C uncoated; 200 °C with sealer |
| Wire purity | 99.5% Al minimum (Al-Mg available for higher temperature) |
| Density of coating | 90-95% of bulk aluminium |
| Operating life | 30+ years in seawater immersion (typical) |
Sealers and topcoats
For most TSA applications we recommend a sealer to fill the surface porosity and improve appearance:
- Vinyl sealers for atmospheric exposure
- Aluminium-pigmented epoxy for immersion service
- Polyurethane topcoats where colour and gloss are required
- Silicone-based topcoats for high-temperature service (200 °C+)
Standards
- ISO 2063-1 — thermal spraying, zinc, aluminium and their alloys
- NORSOK M-501 — surface preparation and coating, offshore
- AWS C2.18 — guide for the protection of steel with thermal sprayed coatings
- ASTM A1059 — aluminium and aluminium-alloy coatings on steel
- NACE SP0386 — cathodic protection of steel structures
Common questions
TSA vs hot-dip galvanizing — when do you pick TSA? HDG is cheaper and faster for general structural steel, but tops out around 50-100 µm and can't be applied to assembled structures or to carbon steel above ~150 °C service. TSA goes thicker (up to 500 µm), can be applied in-situ to assembled structures, and tolerates much higher service temperatures.
TSA vs paint systems — what's the trade-off? TSA costs 2-3× more than paint per square metre but lasts 30+ years vs 7-15 for paint in marine atmospheric service. Total lifecycle cost is lower for offshore where re-coating is expensive.
Can TSA be applied in the field? Yes — we operate field TSA spray equipment for situations where shop application isn't viable. Application requires controlled humidity and temperature; we provide enclosures where needed.
