Although steel is strong, it’s also sensitive to rust. We now have six coating halls in Rotterdam, where monopiles are coated in order to extend their lifespan in salt water. This is also where we make the markings for installation. Siewerd Hartenhof has been our Quality Control Engineer for corrosion protection for a year now.
‘The most important thing is that the coating adheres well. But you can only make this happen if you carefully go through all the steps of the process and clean the monopile under high pressure between each machining step, so that no dirt can get to the paint. With two-component coating, the ratio between the two components is extremely close. It is mixed in the pump by computer control while it is being sprayed. Environmental conditions such as temperature and humidity are also extremely important for the quality of the coating. The temperature is usually between 21-23 degrees. The humidity must be no higher than 80%, otherwise there is a risk of microscopically small moisture droplets on the steel.’
Standards and tests
‘Coatings need to meet strict standards (ISO 12944-2). We prepare the correct documents and test reports for every client. We record all the conditions and make a test plate of each step. These are plates that we treat in every coating operation, for every monopile. The corresponding pull-off test confirms the coating’s adherence and strength. At the end of the process, we go through everything with the client and perform the test of completion – the final check. All documents, tests, and forms together constitute the “as built” documentation, i.e. the paper delivery of the product.’
There are an incredible number of different coating systems, and every system has advantages and disadvantages. That’s why we usually use a combination. One part is done manually (the hard-to-reach parts), and one part is done automatically. One part is done with epoxy (multiple coating layers), and the most fragile parts are done with aluminium or zinc (metallizing). The latter is by far the strongest and lasts the longest, but it’s also expensive. So you work very specifically, around the flange for example. For Borssele 5, large-scale automatic application of thermally sprayed aluminium (TSA), was used for the first time. This is pure aluminium – an expensive material that’s difficult to apply, but very strong. It’s a promising technique that will become more affordable through automation.’