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New coating resists corrosion and biofouling

TWI is among a group of seven organisations collaborating on a project that has developed a new coating technology to protect offshore steel structures from corrosion and biofouling.

Pioneered by the oil and gas sector, thermally sprayed aluminium (TSA) has an excellent track record in providing long-term corrosion protection for steel. It corrodes at a slow (<10µm/yr) and predictable rate in seawater and, unlike organic paints, also provides local sacrificial protection. Thermally sprayed aluminium not only preferentially corrodes in regions of damage, hence preventing the steel itself from corroding, but it also ‘seals’ exposed areas of steel by promoting the precipitation of insoluble deposits from the seawater.

Combining approaches

Now research carried out under the EU-funded ACORN project has combined TSA with eco-friendly, low-release-rate biocides, capable of preventing barnacles from settling on surfaces. Barnacle settlement causes huge amounts of damage, cutting through paints, blocking key access points and making structural inspection problematic as well as promoting further settlement of other marine species, further compounding the problem of bio-accumulation.

Barnacles settle on surfaces and breach through protective paint layers, causing extensive damage to the surface
Barnacles settle on surfaces and breach through protective paint layers, causing extensive damage to the surface

Developed at TWI, this new coating technology has now been extensively tested in simulated offshore conditions and shown to corrode at a steady rate of ~2µm per year. Two sets of field trials were undertaken in 2015, one off the coast of Sweden and the other off the Northern Spain coast. Despite an anomalously low year for barnacle settlement, the results show promise in preventing biofouling. 

Keeping turbines in service

This research has been carried out primarily to benefit the emerging offshore renewable energy market, where static structures need to be moored offshore for prolonged periods of time. In these cases, periodic dry docking is often impossible and in-situ maintenance is difficult and very costly. When total life-cycle costs are considered, application of a highly robust, long-lasting coating that provides protection from both corrosion and biofouling has the potential for significant through-life cost savings and reduced maintenance budgets.

For more information about the ACORN project, visit www.acorn-project.eu. To find out more about TWI’s expertise in coatings technology, please email contactus@twi.co.uk.

Left unprotected, steel rapidly corrodes in seawater. TSA provides local sacrificial protection and long-term corrosion protection
Left unprotected, steel rapidly corrodes in seawater. TSA provides local sacrificial protection and long-term corrosion protection
Avatar Henry Begg Section Manager - Surface, Corrosion and Interface Engineering

Henry joined TWI as a Project Leader in 2013 having completed a PhD on the processing of advanced aluminium alloys. Since joining, he has managed a range of R&D activities relating to coatings and surface engineering across a diverse set of industry sectors. For the past three years, he has led the surface engineering team and has recently also taken management responsibility for the electrochemical corrosion and permeation testing activities at TWI.

Surface engineering activities at TWI span a broad range of process technologies and applications, from thin, functional coatings that create repellent surfaces, right up to thick weld overlays for heavy-duty industrial service. The surface engineering team has a particular focus on thermal and cold spray technology, providing support to industry across a wide range of TRL/MRL levels. They assist TWI members in developing new materials and processes, providing characterisation and performance testing in bespoke environments and supporting the automation and coating of large demonstrator components.

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