Due to the high and diverse stresses involved, the fastening components used in wind turbines are high-strength grades. These are susceptible to brittle fractures, which are usually the consequence of hydrogen penetration during the surface treatment process. This is something that needs to be taken into account when selecting anti-corrosion protection.
The protective coating also has to fulfil specific requirements. Zinc flake systems are able to fulfil them as a package. The basecoat, Delta®-Tone, provides active cathodic protection and with a layer thickness of just 10μm regardless of layer build-up, shape of the parts or type of application. The coating can be applied using all standard application methods; which method to choose depends on the size and shape of the parts. For large steel components, like those used in wind turbines, the methods are primarily spraying or spin coating. As no hydrogen is introduced in the coating process, it is possible to rule out any danger of the high-strength components suffering hydrogen embrittlement. A subsequent organic topcoat – the best choice here is Delta®-Seal, as this system is established for more than 30 years – enables the anti-corrosion protection to be increased significantly.
In August 2012, Germanischer Lloyd has granted this system of Delta®-Tone + Delta®-Seal certification for general use on standard bolts for wind energy plants in the onshore and offshore fields. The main applications are fixings of rotorblades or high-strength fasteners in the gondola with typically dimension of M24-M48. The system is now in use worldwide with almost all well-known manufacturers of wind energy plants, as it offers a safe and economical alternative to the conventional surface protection systems often used in wind energy plants.