Demo Cases

The European Marine Energy Centre (EMEC), is the first and only centre of its kind in the world to provide developers of both wave and tidal energy converters with purpose-built, accredited open-sea demonstration facilities.

With 14 grid-connected test berths, there have been more marine energy converters deployed at EMEC than at any other single site in the world, with developers attracted from around the globe to prove what is achievable in some of the harshest marine environments. EMEC is also at the forefront in the development of international standards for marine energy, and is forging alliances with other countries, exporting its knowledge around the world to stimulate the development of a global marine renewables industry. EMEC has first-hand experience in how issues with materials can cause significant challenges for technology developers. This project will support the development of solutions for marine energy converters, subsystems and connectors that are costs effective, reliable and can survive the demanding requirements the environment places on technology.

WHERE

Orkney Islands, UK

GOALS AND CHALLENGES

To date, most wave and tidal energy converters demonstrated at EMEC have been painted steel structures, or reinforced concrete, with some sub-structures in polymer composites. Trials of various coating technologies have been carried out across the broader marine energy sector with some concrete, composite and plastic structures being developed, however these opportunities have not been explored in full despite being employed extensively in other industries. There are also very few marine energy technologies that have been deployed long term where issues around corrosion become much more significant.
Key focus areas for EMEC will be floating technologies (wave and tidal) which operate in a highly exposed, oxygenated environments with limited access for O&M. EMEC will work with our technology developers (which includes Wello, CorPower, Laminaria, Scotrenewables, Magallanes, Tocardo and Nautricity) to outline a detailed set of emerging challenges to be resolved during the project. This is likely to include the costs of materials, fatigue performance, buoyancy, wear of sub-systems, effects of bio-fouling, device mass and manufacturing of complex shapes. In addition to this EMECs offshore infrastructure has been in place since 2003 which includes cardinal buoys, subsea cables, data monitoring systems, connectors, foundations etc. Challenges facing this infrastructure through corrosion are also sought. As the wave and tidal energy sector is emerging a key outcome will be the identification of supply chain solutions that have been employed in other industries or are emerging from the supply chain that have the capability to benefit the marine energy sector.

SSE are the biggest renewable energy producer in the UK, with 6.8 GW of renewable energy capacity. We operate a large portfolio of on and offshore wind farms, totalling over 2,000 turbines.

SSE operate Greater Gabbard which is one of the 10 largest offshore wind farms in the world, based out of Lowestoft, UK totalling 140 wind turbines, 2 substations and producing up to 504 MW. We are currently constructing Beatrice which has 84 wind turbines, 2 Offshore Transmission Modules and will produce 588MW. SSE also operates Arklow Bank Wind Park in Ireland with a capacity of 25MW. SSE also have a range of new sites in development, from Dogger Bank the world’s largest planned developed to Arklow in Ireland and Seagreen in Scotland.

WHERE

Greater Gabbard and Beatrice

GOALS AND CHALLENGES

SSE are interested in seeing innovative in corrosion management and remediation. As the UK’s offshore wind portfolio ages, corrosion will become a major factor in maintaining asset integrity and be a significant limiter in looking at asset life extension.

SSE have experienced corrosion which requires remediation in the following areas:

• Boat Landing Fenders. Boat Landing Fenders are utilised by CTVs (crew transfer vessels) to push on and transfer personnel to the asset. These areas experience wear from usage and sit within the splash zone, where salinity is very high. Offshore wind farms often have a tidal range of approx. 3 metres which means at times sections with corrosion are submerged. The foundation has an impressed current cathodic protection (ICCP) system which mitigates the corrosions rates causes, but does not prevent it all together. We are looking at reactive paint or air/water tight wrap solutions for this area.
• Other External Transition Piece (TP) Corrosion. Occasionally, other factors cause corrosion, such as suspected TP contacting from floating objects. Remedial actions likely to be similar to the above.
• Access Hook On Locations. On access routes up to the wind turbine (WTG) tower, we have a number of hook on points which personnel clip onto in their harnesses. These are areas without collective protection, so working at height gear is mandatory. Consistent clip-ons have led to paint loss and corrosion, especially on the horizontal bars and lower sections of ladder. Salinity can often be 300 micrograms per square metre, many current paint solutions requires less than 50 micrograms, so several washes are required. The bars are critical to access and must be maintained to have a safe working load of 500kg for fall arrest purposes. Paint solutions and sacrificial wraps are again being considered.
• Major Component Corrosion. In the nacelle, many major components have lubrication systems, such as the gearbox, main bearing. One issue we face when changing these out is corrosion at interfaces, which can lead to lost time during remedial works. This can lead to some components being lowered to a jack-up vessel and polished before being re-fitted. No solutions have been offered for this as of yet, but it is more easily remediated.

Simec Atlantis Energy (ATLANTIS) is a global sustainable energy generation company whose core business is to develop and operate large-scale renewable energy projects around the world. It is currently working on projects for tidal stream, tidal range, and waste-to-energy.

Atlantis has a long track record in tidal energy, developing sites as well as technology. Atlantis initiated, and is the majority owner of, the pioneering MeyGen project. MeyGen is the largest operational tidal array in the world, with four 1.5MW turbines installed in the Inner Sound of the north-east corner of the Scottish mainland. MeyGen is also the largest planned tidal array in the world, with an offshore lease for up to 398MW, and marine consents for a first phase of 86MW.

WHERE

Pentland Firth

GOALS AND CHALLENGES

Tidal energy shares the problems of seawater corrosion with other industries, such as offshore oil and gas, offshore wind, and ships. The corrosion protection measures available to these are also applicable to tidal, but Atlantis’ experience of operating tidal turbines has exposed a number of particular areas of challenge.

• Tidal turbines need to be serviced, which entails opening flanged joints to gain access. The standard method of protecting bolted flanged joints is to prepare and paint them in the same way as the rest of the structure. The whole exterior is blasted, prepared and painted in one go in a dedicated paint shop. It is difficult to achieve the same protection integrity when the joints need to be re-opened for maintenance. The complex geometry of threaded fasteners in holes complicates re-coating the joints in a workshop environment. Nevertheless, the joints need to resist corrosion for many years subsea. There are some proprietary compounds that offer the possible protection for flanges, generally in the form of a plastic coating that covers the whole area, but these solutions have not been proven in marine tidal environments. Other possible corrosion prevention measures are to use sealed caps, but again the long-term effectiveness is unproven.

• Turbines are, of necessity, in aggressive tidal flows, which accelerates corrosion. Cathodic protection standards (for example, DNV-RP-B401) does not allow for increased oxidation due to fast-moving flows passing the structure. There are widely varying factors proposed in literature to compensate for flow effects, but no consensus to aid turbine designers.

• Tidal turbines often incorporate sizeable stainless-steel components, such as wet-mate connectors. Stainless materials may also be required for components that cannot be painted but must not corrode. These masses of stainless steel can act as anodes for the rest of the structure, accelerating corrosion. Improved understanding of this, and the ways of mitigating it, would help to prevent localised corrosion. 

• A specific issue for tidal turbines is cathodic disbondment, caused by the effect of cathodic protection on metal components bonded to carbon fibre composite.Better understanding of this effect is required to ensure long life from carbon fibre tidal blades.