Turning the Tide

Turning the Tide

Protecting a steel structure that will be continuously exposed to extremely corrosive conditions for a number of years is a challenge relished by a coating solutions expert. Hempel was asked to do just that when the company was engaged by Orbital Marine Power Ltd (Orbital) to provide a comprehensive coating solution for its world-leading tidal turbine – the Orbital O2. David Heal, Global Head of Renewable Energy & Performance OEM Segments at Hempel, explains.

Orbital O2 is the world’s most powerful floating turbine and is soon to be commissioned off the coast of the Orkney Islands, Scotland. Weighing in at 680 tonnes, the steel structure is capable of producing 2MW of predictable and clean energy from the strong tidal currents that surround the Orkneys. Utilising two turbines which together create a 600m² rotor area, this cleantech innovation is capable of supplying enough energy to power around 2,000 UK homes.

Hempel has been involved in the project from the very start – including the prototype development in 2015. The challenge with Orbital O2 is two-fold. The steel structure itself will float in the ocean for many years and will require long-lasting and robust protection from saltwater and sea air. Coupled with this, the submerged rotors will need a defence against the accumulation of bio-fouling that has the potential to clog up and slow down their movement.    

The development of the coating system began at the prototype stage of O2 with Hempel’s Technical Service specialists working closely with the Orbital team to design and test the optimum solution. When construction of the full-scale turbine began, Hempel’s experts worked with the company that would be applying the coatings – RyBay Corrosion Services – to ensure the paint would be applied correctly and would perform as expected over the long term.

Protection from corrosion

The combination of salt water and oxygen together with the repeated immersion and atmospheric exposure and the potential for impact and abrasion was expected to cause particular problems for the steel tidal turbine. Added to this, the remoteness of its installation meant that access for coating repair would likely be dangerous, costly and time-consuming. Therefore, the specified coating was required to deliver excellent protection over a long period.

To protect the external steel, Hempel specified two coats of Hempadur Multi-Strength GF 35870 as a high-build coating designed for extremely corrosive conditions including where the steel would be partly submerged in seawater. Not only will this paint protect against corrosion, it is also highly abrasion-resistant and will protect against damage from ice floes. Internally, the steel was painted with two coats of Hempadur Easy.

Hempel’s Hempadur Multi-Strength product is an amine-cured epoxy coating. It is reinforced with glassflake and cures to a hard, impact and abrasion-resistant layer giving excellent protection against seawater. Importantly, it is suitable for early water exposure and will continue to cure under water.

Bio-fouling protection

For the rotors themselves, Hempel’s flagship fouling-defence product – Hempaguard x7 – was specified to prevent the build-up of bio-fouling. Hempaguard incorporates one of Hempel’s most advanced technologies – Actiguard. This works by forming a biocide-activated hydrogel on the surface of the coating and as the biocide diffuses out of the film, it is trapped in the hydrogel layer. This increases the time the biocide is retained at the surface of the coating – where it is most effective. Coupled with this, the silicone coating itself exhibits superior non-stick properties which help to repel organisms trying to attach themselves to the submerged rotors. Since its launch in 2013, Hempaguard has been an extraordinary success and has been applied to more than 2,000 vessels, so it was an easy decision to incorporate this fouling-defence product into the overall solution for O2.

Sustainability at our core

The challenges of protecting O2 required the combined expertise of Hempel’s Protective and Marine divisions. This collaborative and fully-rounded approach was essential is ensuring an optimum solution could be achieved for this innovative project. This project takes Hempel a step closer towards its aim of becoming the global coatings leader in renewable energy solutions and moves the company along its chosen path of embedding sustainability into its core purpose.

As announced in January 2021, Hempel is committed to shaping a brighter future with sustainable coating solutions. It has placed sustainability at the heart of its new business strategy and strengthened its commitment to help customers reach their sustainability targets. This requires embedding a sustainability culture across the organisation including all products and services across the value chain. In practice, Hempel is championing the use of innovative coatings and processes that help its customers reduce their carbon output whilst taking responsibility for its own environmental footprint.

With a core ambition of doubling its energy business by 2025, Hempel’s participation in the ground-breaking Orbital O2 project illustrates its value as a trusted partner as well as the quality and effectiveness of the coating solutions it manufactures.

You can read more articles like this in the current issue of PCE-International