Offshore Wind Farm Maintenance

Dura-Plate 301W, a surface tolerant 2k, is an ideal solution for the repair of larger surface areas.

301W is the latest evolution of the Dura-Plate 301 series of products, with a track record in offshore and onshore applications spanning over 25 years and with over 15 million m² protected in offshore projects alone. It is a low-temperature application and curing version of the Dura-Plate 301K ultra-surface and moisture-tolerant high-solids epoxy coating platform. Dura-Plate 301W may be applied at ambient and substrate temperatures as low as 2°C. It is engineered to provide outstanding adhesion and anti-corrosion performance over a wide range of surface preparation techniques, including water jetting, abrasive blasting, and hand or power tool cleaning. The unique formulation of Dura-Plate 301W allows it to be applied over damp and medium flash-rusted metal substrates (tolerant to Wa2 M – ISO 8501-4) and without dew point restrictions. It is tolerant to low surface profile roughness and is easy to apply with a single-leg airless spray, brush, or roller. A typical coating system would be 2x125-150 microns. These characteristics significantly broaden the acceptable application windows to drive efficiencies in coating schedules for both new construction and maintenance projects, and thus ideal for offshore wind tower structures.

301W has been assessed by operators in both the offshore and onshore energy sectors for its adhesion to damp, low profile and abrasive blasted surfaces and its suitability as a surface and humidity-tolerant coating to reduce traditional downtime in maintenance painting due to weather conditions.

The performance of a single coat of 301W on rusty steel (prepared to St3) was assessed after 5,000 hours of exposure to artificial weathering (ISO 11507) [3] and humidity (BS 3900 F2) [4].  No coating defects were observed in either test.

Third-party testing confirmed the excellent adhesion of a single coat of Dura-Plate 301W at an average DFT of approx. 250 microns to various substrates (damp, low surface profile), all cured under 100% relative humidity, with average pull-off adhesion above 15 MPa, and where the failure mode was either cohesive or partially glue failure (Figure 1).

No detachment was observed between the coating film and the substrate in any of the twelve pull-off readings performed over six panels. In addition, no meaningful difference or trend was detected between the adhesion over dry abrasive blasted steel and adhesion over damp or smooth non-blasted steel. Curing at the 100% humidity and temperatures tested was normal and did not impact the results. A third-party laboratory was commissioned to carry out flexibility testing of Dura-Plate 301W coated samples using a four-point bend method. Ten sample plates (250 x 25 x 6 mm) were coated with a single coat of Dura-Plate 301W at an average DFT of 220 microns and evaluated at 3% and 5% strain testing (Figure 2).

In a further evaluation by an offshore maintenance services company, the report stated that during application, it was clear that the 301W was easy to apply with brush and roller, that the coating spreads smoothly, and that once dried, the surface becomes smooth and glossy. When applied with a brush in the usual manner, it's easy to achieve a dry film thickness ranging from 150 to 200 µm. With the necessary attention, a dry film thickness of 250 to 300 µm with just one coat on flat and easily accessible surfaces was easily achieved.   The adhesion of the 301W on a Sa 2.5 blasted substrate was good. Even under extreme conditions (exaggerated) with a too-wet surface, the adhesion remained good, and the adhesion on the substrate exhibiting heavy flash rusting (Grade H) even achieved an adhesion value of 8 MPa. When evaluated as a maintenance coating system at an onshore asset, it was found to be effective in reducing downtime during scheduled maintenance by around 70%, which computed to cost savings of approximately £135,000 ($170,000 USD). 

For small area (spot) repair, Repacor SW-1000 is very suitable and has a good record in this application. The advantage of this product is that it is a two-component solvent-free ultra-fast drying coating supplied in a cartridge, which can easily be applied by less-skilled staff, e.g. rope access technicians (Figure 3).

Repacor SW-1000 is the result of a three-year research product by Sherwin-Williams to develop a coating solution that could simplify maintenance repair work on offshore wind structures. The safety of rope-access applicators using this product was also a prime consideration in the development. Compared to the 2-3 layers needed with traditional technologies, it requires only a single layer coating, easily dispensed using a standard sealant gun, without the need for mixing, to obtain the necessary performance. Repacor is compliant with NORSOK M-501 [1] and meets the highest standards in anti-corrosion protection. Repacor SW-1000 has all the properties of traditional multi-coat protection systems built into a single coat of 500-micron dry film thickness. Despite the single coat, it is expected to mimic the original performance of offshore wind structure coating systems. It is UV-resistant and no additional topcoat is needed, which is a major advantage in offshore environments. It also has a cure time that is around four hours faster than alternative aerosol systems, and the unique cartridge application process means the applicator can effectively work from a backpack, so it only requires one visit to carry out the repair, whilst waste packaging is also minimized. 

Both a battery-operated bristle blaster for surface preparation and the Repacor cartridge can be carried in the backpack of a rope access technician, enabling an easy-to-apply 1-coat fix, saving money and time. In addition, one of the main properties needed from a repair system is good adhesion to the existing substrate after suitable preparation, together with continued good corrosion protection. Third-party testing was carried out to determine both the adhesion of Repacor SW-1000 and its suitability for providing corrosion protection in this environment.

Coated steel panels, which had been exposed to a corrosive environment, were repaired using Repacor SW-1000 and then subjected to 4,200 hours of cyclic corrosion protection tests in accordance with ISO 20340 Annex A after removal of the damaged coating by spot grit basting to SA 21/2, and manual application of one coat of Repacor SW-1000 at 500 microns DFT.

After testing, the panels were visually assessed, followed by adhesion testing and measurement of corrosion at the scribe. The results are given in Table 1 and Figure 4.  

Repacor SW-1000 transforms the maintenance and repair of offshore wind turbine towers and additionally provides an excellent solution for onshore industrial environments where a simple-to-apply, high-performance, durable and cost-effective coating is required.

Repacor SW-1000 Application Process

Table 1: Repacor SW-1000 Test Results

Evaluation before exposure

Evaluation after exposure

Duration: 4200 hours (500 microns)

Testing was carried out by Fraunhofer IFAM, Bremen, Germany, and results are reproduced with approval.