Whether from oil rigs, wave and tidal energy converters or wind farms, many of our energy needs are met by offshore sources. Although these areas tend to be rich in resources, the challenge is to find more cost-effective ways to exploit them. Adding to the challenge are the harsh conditions they face – including paint degradation by UV radiation, seawater corrosion and high wind speeds. This translates into a limited lifespan for these expensive structures.
“Steel structures in marine environments are subject to many forms of degradation, two of the most problematic being corrosion and biofouling,” said surface engineer Henry Begg of the EU-funded ACORN project. “Although coatings to protect against such conditions exist within the shipping industry, where ships can be periodically dry-docked for maintenance, offshore structures are required to be moored in the water for extended periods of time and without ongoing preventative maintenance.”
To rectify this structural issue, Begg and the ACORN project team have developed an innovative protective coating that extends the lifetime of marine structures. The durable, non-paint solution can work on an array of offshore steel structures used for the production of renewable energy, including wind turbine foundations and wave or tidal energy devices, as well as conventional offshore infrastructures (such as docks, buoys and oil/gas rigs).
When the new coating is used, not only do these structures enjoy an extended and virtually maintenance-free lifespan of over 20 years, the need for supplementary (and costly) cathodic protection is also reduced – or even avoided. As a result, the project is boosting the competitiveness of the industry and helping to facilitate widespread roll-out of additional offshore technologies.
Thermally sprayed aluminium
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Left unprotected, steel rapidly corrodes in seawater. TSA provides local sacrificial protection and long-term corrosion protection[/caption]
The ACORN solution bases its technology on thermally sprayed aluminium (TSA). TSA is a coating with proven, long-term resistance to corrosion in offshore environments. This TSA coating is then enhanced with a range of environmentally friendly, active anti-fouling substances that do not need to be released into the water. Instead, they act locally from within the coating to prevent the attachment of biofouling organisms. The substances are added in very small concentrations, allowing them to be gradually exposed at the active surface of the coating as the TSA corrodes (typically at a rate of <10µm/year).
The eco-friendly anti-fouling substances were specifically chosen for their performance, commercial availability and regulatory approval for use in EU waters. In order to ensure the anti-fouling carriers were capable of withstanding the offshore conditions, researchers also evaluated their resistance to seawater corrosion, UV radiation damage and settlement of fouling organisms, with a particular focus on barnacle colonisation.
“Barnacles represent one of the most damaging biofouling species and can block a structure’s key access points, cut through protective paints and promote the settlement of further marine fouling organisms,” explained Begg. “We ultimately chose TSA because of its excellent track record in the oil and gas sector for providing long-term corrosion protection. Not only does it corrode at a very slow and predictable rate, unlike paints, it also provides local ‘sacrificial’ protection that protects the steel substrate even if the coating is damaged.”
With the ACORN project’s solutions now in the commercialisation phase, researchers are confident that their work will provide the market with an environmentally safe solution.
“As global energy demands shift, renewable energies will likely see the construction of more offshore energy installations over the next decades,” said Begg. “Having these installations protected with the coatings developed by the ACORN project helps ensure that the production of sustainable energy is itself sustainable.”
© European Union, 2017