15 March 2016
The offshore turbines are built to last about 25 years but what about the paint on the first generation of turbines? Hempel makes a status.
The investigation was primarily carried out by visual inspections, photographic documentation and dry film measurements.
Zero maintenance due to corrosion. That is the overall conclusion of the survey that Hempel have carried out in cooperation with Vestas and Vattenfall to identify the durability of the paint that the company has delivered to the wind turbine towers at Horns Rev 1 and Thunoe Knob.
“Our estimate is that the paint will last another 15 years without corrosion which means that the total lifetime of the paint is at least 25 years,” explains Chief Engineer in Hempel Group R&D Niels Lund Jensen. He is specialised in the development of Hempel’s products against corrosion.
“The rule of thumb is that if there is no corrosion after a couple of years, the paint is very likely to have a long durability. If our survey show no corrosion after approximately 12 years our track records show that there is a great probability that the paint will last up to 25 years and more,” he adds.
The thickness of the painting is crucial when it comes to protection against corrosion. For offshore constructions the adequate thickness is 300-400 micrometers. The tests showed that in some areas of the towers at Thunoe there was only half this amount, still the paint protected against corrosion.
He explains that the towers at Horns Rev in the North Sea are exposed to much more harsh weather conditions including a higher concentration of salt than Thunoe Knob near Aarhus in Kattegat. This makes the condition result at Horns Rev even more interesting for the possibilities of export to countries with similar harsh climate.
The new generation of paint
During inspection some damages were spotted. For instance by the bolts that fasten the rope around the towers at Thunoe Knob that function as a kind of liveline that personnel can hold on to when working at the turbine. When the wind blows, the bolts hit the tower and make holes in the paint.
“We could see that the paint had disappeared in those areas, and that there was minimal corrosion The rest of the paint was intact, so the corrosion had not dissipated. That is conclusive evidence that the paint will last,” Niels Lund Jensen mentions.
The paint used at the offshore windfarms a decade ago is of course not identical with today’s products among others due to more severe environmental requirements. The amount of solvent in the paint has been reduced either by so call higher solid paints or paint where a large part of the solvent has been replaced by water, however, the paints are still comparable to the previous products when it comes to durability. The waterborne paints can be a special challenge as the hydrous material does not tolerate frost during application and handling and there is a small price premium due to the production process involved.
Hempel is constantly working on developing their paintings to be more long-lasting and also more eco-friendly.
“As laboratory tests are not yet reliable enough to fully predict durability, we are very satisfied that we can document some of our products and solutions to our customers through the fine performance of the products offshore. This is an advantage for them and for us,” says the Chief Engineer.