Offshore wind developers and companies with technology that could help them tackle corrosion are collaborating to bring forward new solutions
Corrosion of structures installed offshore is extremely expensive to deal with. Preventing it from happening wherever possible is the key. New types of technology are required, over and above those developed for the offshore oil and gas industry and transposed into offshore wind.
And as with so much of the technology developed to reduce costs in the industry, a collaborative approach is the key to developing, testing and introducing into service new concepts, as two recent projects highlight.
The first project, Cost Reduction for Offshore Wind Now 1 (CROWN 1), saw the ORE Catapult in the UK working with The Welding Institute, also in the UK, and consultancy LIC Engineering in Esbjerg, Denmark, to demonstrate the technical and economic feasibility of using thermally sprayed aluminium to protect monopile foundations from corrosion.
Also participating in the project were offshore wind developers EDF Energy and Ørsted, Wilton Engineering Services, Universal Coatings, a specialist in surface preparation and coatings for offshore structures, and Metallisation, a company that specialises in metal spraying equipment. The £1.2M (US$1.5M) project was funded by Innovate-UK .
ORE Catapult project manager Jude Ogwu explained that thermally sprayed aluminium could be particularly important in the offshore wind industry because, firstly, it seems to be effective in other, related corrosion control applications; and secondly, because it can help reduce the levelised cost of energy through reduced capex and curing times, because it is easier to apply than some other corrosion protection products. Another important advantage is that compared to alternative corrosion protection techniques such as cathodic protection (CP), thermally sprayed aluminium is unlikely to need the same level of maintenance.
The scope of the CROWN 1 project ranged from investigating thermally sprayed aluminium application methods, to investigating its behaviour during piling and exposure to corrosive environments in the field. The ORE Catapult also carried out lifecycle cost modelling to compare thermally sprayed aluminium with other conventional methods of corrosion protection such as paint formulations and sacrificial anodes.
Field tests began in June 2017, with simulated piling operations taking place at the ORE Catapult’s drydock facility. The mechanical damage from these trials was assessed following seven months of simulated offshore operation, before a lifecycle cost modelling phase of the project.
A follow-on project, CROWN 2, recently got under way, building on the work completed in CROWN 1. It includes an offshore field trial of thermally spray-coated materials and laboratory studies to understand the operational properties of thermally sprayed aluminium, such as acidification and its interaction with other materials such as paint.
A spokesperson for the ORE Catapult said CROWN 2 will also look into the effect of thermally sprayed aluminium on the fatigue life of coated steel, as well as interaction with materials used in other corrosion protection systems, such as cathodic protection materials such as CP or impressed current cathodic protection (ICCP).
There are eight industry partners involved in seven work packages (WPs) in the project. The ORE Catapult is part of WP2, which is carrying out the offshore corrosion trials in order to characterise the performance of thermally sprayed aluminium in a harbour/mudline environment.
“A total of 12 tubular monopiles, six with epoxy coating, six with thermally sprayed aluminium, were piled into the artificial seabed in Dock 2 at our National Renewable Energy Centre in Blyth in January 2019,” said the ORE Catapult. “The dock was filled with seawater and the condition of the seawater and seabed are being monitored.
“This is a long-term installation involving periodic removal and inspection of the monopiles, with half of them due to be taken out in January 2020. Three of those removed will be epoxy-coated and three coated with thermally sprayed aluminium. The remaining piles will be removed in January 2021 and a full analysis/assessment of corrosion performance of all coatings carried out. The ultimate aim is to analyse the performance of different corrosion protection coatings in near real-world environmental conditions.”
Coatings applied to offshore components need to be able to prevent corrosion, but must also be easy to apply and suitable for use on large structures
The second collaborative project also involved developers and technology providers and is known by the acronym NeSSIE (North Sea Solutions for Innovation in Corrosion for Energy). The project, co-funded by the EMFF programme of the European Union, started in May 2017 and was completed in Q2 2019. Its aim was to identify corrosion challenges facing developers of offshore renewable projects and match them up with companies with technology that could be used to address those challenges and tested in demonstration projects.
Funded by the European Maritime Fisheries Fund (EMFF) and developed through co-operation between regions participating in the Advanced Manufacturing Pilot, part of the Vanguard Initiative, the two-year project saw a consortium of partners work together to define three bankable demonstration projects in the North Sea.
At the end of Phase 2 of the project in October 2018, participants in NeSSIE heard from developers who have corrosion-related challenges they would like to address, among them SSE, which is looking for solutions to corrosion management and remediation for offshore wind turbines.
Supply chain companies were put forward to meet project developers in January 2019 and it is hoped they will now have the chance to work with them to develop business cases for demonstration projects. Developers were also expected to help identify potential funding packages to deliver the demonstrations.
Eight partners from five countries participated, including Scottish Enterprise, the Basque Energy Cluster (Spain), ASTER (Italy), Sirris (Belgium), Svenskt Marintekniskt Forum (Sweden), University of Edinburgh (UK), Fundación Asturiana de la Energía (Spain) and the Lombardy Energy Cleantech Cluster in Italy, in addition to an industry advisory group including Dalarna Science Park (Sweden), the Offshore Energy Cluster (Denmark), MERINOVA (Finland), Highlands and Islands Enterprise (UK), and SPRI Group (Spain).
Apart from introducing new technology that can prevent corrosion in offshore windfarms and other renewable energy installations, the participants in the NeSSIE project believe commercialising anti-corrosion solutions for marine renewable assets will provide market opportunities for the supply chain in Europe and add value to the offshore industry at European level.
Thermally sprayed coatings – what are they and how do they work?
Thermal spraying (or metal spraying as it is also known) is a surface engineering/coating process that sprays metals, ceramics and polymers onto the surface of another material. It is widely used to provide corrosion protection to ferrous metals, as well as to change a structure’s surface properties, for example to improve the wear resistance or thermal conductivity.
In other industries it has been shown to extend the life of structures, equipment and vessels for which protective surface coatings are essential for their longevity.
There are four main methods of thermal spraying, all of which project small molten or softened particles onto a surface to adhere and form a continuous coating. The temperature increase of the coated part is minimal, meaning heat distortion is rare, which is a major advantage over hot-dipped galvanising or welding.
Thermal spraying for corrosion control is usually carried out by flame and arc spray, which are the least costly and quickest techniques to implement, so are suitable for corrosion protection of larger structures. Plasma and high-velocity oxygen fuel (HVOF) coating is a thermal spray coating process used to improve or restore a component’s surface properties or dimensions. HVOF sprays are usually used to apply engineering coatings, and are of a higher quality, density and bond strength.