Power Take Off steel rods are key components in wave energy. Their surfaces are exposed to among others, marine corrosion, marine biofouling, and mechanical wear. Protective coatings are sought for, and test and validation protocol for these coatings are needed. In this study metallic matrix coatings applied by laser cladding, have been tested. Accelerated testing and field methods have been employed. The goal is to use these coatings as study case for evaluation of methods itself for corrosion and wear resistance validation. The methods and preliminary results are presented and discussed. In particular: a) field test of a biofouling control strategy using mechanical scraping at different intervals; b) continuous salt spray test in three different media (conventional NaCl; artificial seawater; and natural seawater); c) cyclic potentiodynamic polarization measurement (ASTMG61) for ranking of nickel- and cobalt-based coatings and study susceptibility to localized corrosion; d) Critical crevice temperature test for nickel-based alloys (ASTMG48–D); d) Multi-degradation testing where synergy effects from wear and corrosion are considered (only discussed). The goal is to evaluate methods and experimental design to both reduce uncertainty, assist in material selection, and finally provide a pathway for final validation of PTO coatings toward a third-body certification.
Harvesting ocean energy will play an important role in supplying fossil-free energy for future generations.1 The oceanic environments around the world are unfortunately of the toughest possible to operate in. Most technologies use a power take-off (PTO) unit with mechanisms that are placed inside protective enclosures or sealed buoys to protect from the harsh environment in seawater. This gives a barrier from the corrosive electrolyte and biological activity that can deteriorate the components. The energy from the oceans in form of relative movements and forces are transferred to the PTOs with help from complex dynamic sealing systems. To guarantee their performance and reliability, dynamic sealing systems include engineered surfaces (for example hard metallic coatings on piston rods), combined with specific polymer sealing materials that can cope with high velocities and provide good media separation. These elements operate together and need to be kept in good condition of cleanliness over their entire lifetime. One need to find an optimal combination of properties from the system which can minimize risks from corrosion, wear, and biofouling. To ensure a high level of reliability efforts need to be focused on R&D, tests, and demonstrations of critical subcomponents such as PTOs, seals, and moorings.2 This work has focus on reliability testing for biofouling and corrosion mitigation which is also linked to the wear of coatings and seals. The study case is a wave energy converter (WEC) developed by "CorPower Ocean AB" and the test methods aim to creating valuable knowledge on antifouling and anticorrosion solutions to minimize risks and maximize reliability of components in the marine energy sector.
