Research study: qualifying offshore-wind repair coatings — and the surface-prep step behind them (RepaKORR)

RepaKORR was a German government-funded research project into repair systems for the anticorrosive coatings of offshore wind structures. Its work on damage assessment, accelerated ageing of repair coatings, and offshore application procedures put mechanical surface preparation — coating removal and profiling with a rotating bristle tool — at the centre of the field-repair sequence.

The project

RepaKORR (“Repair systems and concepts for anticorrosive coatings of offshore wind structures”) was funded through the German Federal Ministry of Education and Research (BMBF, project 03X3570A). It brought together Muehlhan AG (application procedures), Fraunhofer IFAM (qualification and verification; temporary protection), Sika Deutschland (repair materials), AirRobot (inspection drone), Corroconsult (damage assessment), RETC (regulatory and environmental issues) and WeserWind (design and logistics). Results were presented in industry sessions and at Eurocorr in 2016–2017.

Why offshore coatings fail

Analysing coating damage on platform-type structures, the project attributed failures roughly to: mechanical damage (~30%), unfavourable design (~30%), insufficient coating (~24%), welding (~11%) and environment (~5%). Much of the mechanical and design-related damage occurs in exactly the places that are hardest to inspect, blast-clean, paint and repair — corners, openings, connections and areas with poor access, as also recognised in ISO 12944-3.

The offshore field-repair sequence

The project set out a five-step field-repair procedure for offshore structures, carried out largely by rope-access technicians:

1. Access & protection / housing — reach and wrap external areas, and access internal sections.
2. High-pressure water washing — remove dirt, impurities and soluble salts (notably chlorides) from the substrate.
3. Blast-cleaning — wet blasting in the atmospheric, splash and tidal zones, followed by fine cleaning.
4. Power tooling — coating removal and profiling with a rotating bristle brush, de-rusting with a grinder, scale and rust removal with a needle hammer, and weld-seam cleaning with a power brush.
5. Paint application — by roller, cartridge or brush.

Step 4 is where mechanical surface preparation earns its place: in confined, access-limited and splash-zone areas where wet-blasting is impractical, a rotating bristle tool removes the failed coating and generates the anchor profile in one grit-free step — the same principle behind the Bristle Blaster®.

Qualifying the repair coatings

Fraunhofer IFAM subjected candidate repair coatings to accelerated ageing and to the mechanical tests used for certification, including:

• Impact strength (falling-weight, ASTM G14): greater than 3.4 J for non-deck areas and greater than 5.6 J for decks and the boat-landing splash zone.
• Abrasion resistance (Taber, ASTM D4060): coating-thickness loss under 50 µm per 1,000 cycles.

Together with ISO 12944 corrosion-category context, these criteria define whether a repair system applied under offshore field conditions can be expected to last.

The takeaway for surface preparation

A repair coating is only as durable as the surface it is applied to. RepaKORR’s field procedure shows why grit-free mechanical preparation — coating removal and profiling in a single step — has become a standard tool in the offshore repair kit, especially where abrasive blasting cannot reach or cannot be used.

This article summarises publicly presented research from the RepaKORR project for reference. MontiPower was not a formal project partner; MONTI rotating-brush tooling is shown in the project’s documented offshore application step.