Evaluation of Two Repair Methods for Duplex-Coatings

The economic use of offshore wind turbines requires a reliable and long-lasting corrosion protection. Sophisticated multi-layer coating systems consisting of a thermal spray coating – mainly ZnAl15, a sealer and several layers of organic coating have been proven to provide such protection. Damages to these duplex-coatings can however not be prevented necessitating on-site repair works. In case of severe damages, the remaining coating close to the damage is often removed and subsequently, the duplex-coating is rebuild from scratch. In the present study, two integrated coating removal and substrate pre-treatment methods are investigated. For this purpose, duplex-systems were produced, artificially damaged by milling and afterwards treated by either grit-blasting or with a rotating steel-wire brush, i.e. a Monti Bristle Blaster, commonly presented as superior solution on offshore corrosion conferences. Afterwards, the duplex-coating was re-applied in the considered area. To evaluate the influence of the pre-treatment method on the coatings’ corrosion protection potential, a 38 week-long salt spray test was used. The test revealed a pronounced influence of the pre-treatment method on the corrosion protection potential. In case of grit-blasting, no corrosion could be detected. The use of a wire brush, however, resulted in coating failure and some spots of red rust.