The industry standards and requirements for the preparation of steel surfaces for surface treatment for corrosion protection in wind turbines involve the following:
Removal of foreign matter: Foreign matter such as oil, grease, dirt, NDT residues, weld flux, and other surface contaminants must be removed using suitable cleaning media and freshwater washing. The cleaning media and methods used must be approved by the paint supplier.
Removal of salts and water-soluble impurities: Salts and water-soluble impurities must be removed through high-pressure cleaning with freshwater, with special attention to areas around welds and difficult-to-access areas. The maximum permissible content of soluble impurities on the blasted surface is specified, corresponding to a maximum NaCl (salt) content of 50 mg/m².
Blasting abrasives: Blasting abrasives used must be dry, clean, and free from contaminants that could adversely affect coating performance. ISO 11127-6 applies to non-metallic abrasives. The size of abrasive particles must achieve the required blast profile for the chosen coating system.
Protection of threaded holes: All threaded holes must be protected from abrasive blasting particles, paint, and metallisation particles as specified in the provided specification.
Abrasive blasting for steel surfaces: Abrasive blasting for steel surfaces prior to painting must meet cleanness level Sa 2½ according to ISO 8501-1 (SSPC SP10). Specific roughness requirements are defined, and particular attention must be paid to achieving the correct blasting profile on weld seams and hard-to-reach areas. Mill scale residues are not acceptable.
Cleanness of surface prior to painting: Moisture, particles from blasting, dirt, and dust must be removed from the surface before painting. Shop primer on offshore structures must be fully removed by abrasive blasting.
Re-blasting: If the cleanness level deteriorates between abrasive blasting and application (lower than Sa 2½), re-blasting to Sa 2½ must be performed.
Abrasive blasting for areas prior to spray metallisation: Abrasive blasting for areas to be spray metallised must meet cleanness level Sa 3 according to ISO 8501-1 (SSPC SP5). Specific roughness requirements are defined, and similar attention to achieving the correct blasting profile and removing mill scale residues is specified.
Cleanness of surface prior to spray metallisation: Similar to painting, moisture, particles from blasting, dirt, and dust must be removed from the surface before metallisation. Any shop primer must be fully removed by abrasive blasting.
Ambient conditions: Specific ambient conditions are specified, including substrate and steel temperatures, relative humidity, and ambient temperatures for painting and metallisation processes. These conditions must be maintained during surface treatment.
These standards and requirements ensure proper surface preparation to achieve the desired level of corrosion protection for wind turbine components, aligning with industry best practices and quality control measures.