Seawater and steel just don’t get along, which makes corrosion control for the offshore wind industry far more critical than it is for onshore turbines. A wide range of bolt and tower coatings are commercially available. But inspect the facility of any large structural fabricator and you find the paint shop is the choke point of production. Speed up the application of paints and coatings and production flows faster. One coating in particular from developer Hempel is said to be time and cost-efficient for steel towers. And although recent, it has a history.
A case history
Alucrom AB, a supplier to many of Europe’s wind projects, had shot blasted and painted more than 300,000 m² of steel towers in 2008, but was finding it increasingly difficult to keep up with demand. The only way to stay on top of business was to speed up production. The company asked coating manufacturer Hempel A/S if it could deliver a system with faster drying, low-VOC paint which would speed up production.
Hempel turned to Covestro for assistance and the two firms devised a two-coat system based on a zinc-epoxy primer and a topcoat that use Covestro’s Pasquick polyaspartic technology, a range of resins and hardeners. The outcome is a two-coat method instead of the previous three conventional coatings. What’s more, the coatings cure faster. Both factors help to reduce the cycle time and the manufacturing costs of wind turbines.
Tests of the new product consumed about 75,000 liters. Hemple says the corrosion protection is as long lasting and high in quality as the previous materials and process. This is an important prerequisite for turbines intended for long service lives and minimal maintenance.
Covestro says the coating uses a low-viscosity polyaspartic binder in combination with a polyisocyanate hardener to boost productivity in paint shops. The layer reduction from three to two is said to have no negative effects on the quality of the film: The total coating thickness is unchanged, providing protection against seawater and other environmental influences.
“This principle of reducing the required number of coating layers also applies to medium-duty applications,” says Ahren Olson, marketing manager with Covestro. “A frequent challenge facing protective coating manufacturers and applicators is increasing the productivity of coating operations. Covestro’s Paskquick polyaspartic technology requires fewer coating layers, which significantly increases painting efficiency and reduces overall painting costs. This is especially true for the fast-growing market of direct-to-metal coatings where Pasquick polyaspartic technology can be formulated into high film build, fast drying, UV and corrosion resistant coating.”
The end client, Enercon Windtower Production AB, now receives six complete towers per week with an exterior coating of a Dry Film Thickness (DFT) 320 μm and an interior coating of DFT 200 μm. ‘’So far all parties involved are very satisfied,” says Hempel’s Lars Rosen. “VOC emission have been reduced by 30%, and more sections can be produced per day thanks to the shorter drying time.’’ The curing process for a complete Pasquick-based coating build-up takes 6 to 8 hours. This is a significant time reduction compared to conventional three-coat systems, which take a total of 18 to 24 hours to cure. The system is now standard in production as Hempathane HS.
Filed Under: Featured, Offshore wind, Towers