Understanding Corrosion Control on Structures in Offshore Wind

The world is craving renewable energy. Every day, we hear news of the green energy revolution in mainstream media – whether it be hydrogen fuel cells, carbon capture, solar or wind energy. One such booming energy segment is offshore wind, which includes anchored offshore turbines as well as floating wind turbines.

Offshore wind has parallels with the oil exploration segment of energy with regards to corrosion and asset protection due to their mutual hardships, mostly being located in the middle of the sea. With the offshore sector poised for rapid growth across the globe and North America, it is important to dissect the performance needs for material selection and the role that industry specifications play in protecting these valuable assets.

Concerns from investors, project owners and operators of these renewable energy segments focus on some key points – improved asset life, superior corrosion protection and reduced maintenance costs. Sherwin-Williams is dedicated to providing superior support across these areas. Our wide range of subject matter expertise ranges from the framework for material selection, various parameters affecting corrosion, differentiation amongst prevalent industry vs. owner specifications, and how it all ties to sustainability as well as life-cycle assessments of the assets that these coatings protect. We can help customers progress in their renewable energy endeavors while protecting their investments.

THE WORLD WANTS MORE RENEWABLE ENERGY

Recent human efforts have focused on reducing our collective carbon footprint for global environmental benefits, resulting in efforts to spur energy generation from renewable sources. As North America catches up with the demand for offshore wind turbine energy, the need for corrosion protection will only increase.

The next decade will see a boom in renewable energy – with that comes the requirement to address asset installation, protection and maintenance, all critical to asset lifecycle and performance. There is a demand for materials required to bridge the gaps between challenges – the need for higher-performing, innovative materials requiring the least amount of substrate to exceed the asset life cycle is critical.

European conditions versus U.S. conditions for offshore wind are very different because oceanic water temperature fluctuations and weather conditions play a big part in salinity and moisture levels on corrosion of towers, monopiles and rotor blades.

To understand how different types of corrosion work and how they affect assets, we need to understand the performance zones of a typical offshore environment. In offshore wind environments, there are four different stress/corrosion zones in relation to sea water level:

1. Zone four: Atmosphere, internal
   
2. Zone three: Atmosphere, external
3. Zone two: Splash zone, tidal zone, and low water zone
4. Zone one: Underwater zone and seabed (internal and external)

Each zone has its own corrosion control requirements, and with each set of requirements comes a set of mechanisms for corrosion control.

CORROSION ALLOWANCE
The allowance for extra wall thickness on a structure. This includes larger amounts of steel for allowing that particular corrosion to happen – extra wall thickness allows for corrosion loss during life. However, this extra metal adds to material, transportation and installation costs of a project.

CATHODIC PROTECTION
Widely accepted throughout the industry, a protective cathodic current is applied to the asset by sacrificial anodes or an impressed current. Usually, another form of corrosion protection is required in collaboration with this method, most typically protective coatings.

CORROSION PROTECTION COATINGS
This is the most prominent form of corrosion control, and it is often coupled with cathodic protection. This method is the most effective solution, with a proven track record of asset protection behind it.

With each system type comes a set of requirements and specifications set by industry organizations and testing agencies around the world. This sets the criteria and performance requirements of any coating system for corrosion control in offshore wind projects. The most commonly accepted industry specification standards are ISO 12944. NORSOK M-501, VGB/BAW, and DNV-GL are other globally recognized standards. There are independent specifications by project owners like Orsted, GE and others.. Each component of an offshore windmill has a different requirement to match its functionality and performance needs.

• The interior and exterior of the tower usually uses the same coating system with variable film thickness.
  The exterior of the tower requires an additional topcoat that is weatherable and can withstand sunlight/UV exposure.
• Total recommended film thickness: External > 280 μm

STANDARDS FOR OFFSHORE MONOPILES/TRIPODS

• ISO-12944 and Norsok M-501 System-7
• ISO 20340 as a predecessor spec
• Norsok M501, 7A describes Splash Zone
  • Total film thickness > 1000 μm
• Norsok M501, 7B describes Immersed zone, with steel temperature <50 oC
  • Total film thickness > 350 μm
• Norsok M501, 7C describes Immersed zone, with steel temperature >50 oC
  • Total film thickness > 350 μm

Currently, protective coatings provide assets in service up to 25 years of corrosion protection. Any asset owners would prefer to extend this to 35-40 years, as installing these structures and performing ongoing maintenance is costly and time-consuming. To understand how we can better protect these assets and bring more renewable energy to the world, we must understand the corrosive environment types.

There are six different levels of corrosive category environment types based on ISO 12944:

• C1. Very low
• C2. Low
• C3. Medium
• C4. High
• C5. Very high
• CX. Extreme

These corrosive classifications help determine the type of environment and performance testing needed for a particular coating system to ensure the utmost protection based on the particular asset. CX is the harshest performance requirement and the most applicable to offshore wind projects.

There are four immersion environment classifications based on ISO 12944:

• IM1. Freshwater
• IM2. Sea or brackish water
• IM3. Soil
• IM4. Sea or brackish water

IM4 is the most applicable for offshore environments, equivalent to Norsok M-501 7B requirements. Installation takes time and effort – and maintenance is its own obstacle. Maintenance on these structures poses a series of complex challenges, involving:

• Weather conditions
• Severity of the oceanic climate
• Accessibility of the structures as they are submerged underwater
• Wearing specialized gear during maintenance
• High humidity
• Less access space
• Personnel and worksite safety

Selecting a Coating system that meets and exceeds the performance requirements, expected life cycle and asset protection needs, as well as checks the boxes for cost and maintenance concerns can be a complex endeavor for fabricators. Selecting the right suppliers often reduces project pains and extending service life usually results in cost savings. Sherwin-Williams Protective & Marine has the approved coating products listed on numerous of this industry as well as owner specifications, conforming or exceeding the extensive asset protection needs prevalent in this growing energy subsegment of the offshore wind industry.

Many offshore wind structures become locally damaged during and after installation. Modern repair solutions have been developed over the years to keep up with the growing need for maintenance and repair of atmospheric exposure zones of offshore wind farms. Material and process efficiency are key when labor and materials are costly. To achieve highly efficient and durable repair jobs with corrosion protection coating systems and ensure the extended lifetime of offshore wind powerplants, Sherwin-Williams Protective & Marine developed a modern repair coating and procedure.

SHERWIN-WILLIAMS PROTECTIVE & MARINE IS HERE TO HELP

Sherwin-Williams considers three sustainability parameters to ensure our products extend asset life cycle to the greatest possible end timeline: Environmental Footprint, Product Blueprint and Social Imprint. Our corporate sustainability focus aligns well with customer expectations of prolonging asset life and ensuring reduced carbon footprint, to drive a sustainable growth with least environmental impact for future generations.

This not only reduces waste but ensures the energy we produce and the climate are getting the most out of its performance – to maximum expectancy with a noticeably reduced carbon footprint. Dura-Plate® SW-501 is a 100% solid epoxy primer with the least VOC for an Offshore wind project coating, with the higher performance as tested per ISO, Norsok and other industry specifications, also offered in a glass flake version (Dura-Plate® SW-501 GF) that conforms to Norsok M-501 7A. Also, Repacor® SW-1000 is a glass flake 2K polyaspartic putty that offers the least amount of required substrate preparation for a repair product, resulting in noticeable asset longevity. Repacor® SW-1000 is low-VOC, as regulated by the U.S. Environmental Protection Agency. Formulated as a 100%-solids and solvent-free coatings, Repacor SW-1000 is abrasion- and UV-resistant – with an underwater cure, perfect for maintenance or repair on damaged coating areas. Both of these coating systems have a good track record of protecting Offshore wind energy assets.

Sherwin-Williams Protective & Marine is committed to the highest level of customer service, ensuring optimal performance with every application of our products. We offer expert on-site assistance and are here to discuss your challenges and provide guidance for complicated projects with our global industry expertise.

Looking to learn more about specifications and performance requirements, and what it means for your project and corrosion protection needs? Check out our sustainability report published in 2023 for updates on how Sherwin-Williams measures the progress we make in our Corporate Sustainability Initiatives.

ABOUT THE AUTHORS

Dr. Jigar Mistry is a Renewable Energy Market Segment Manager for Sherwin-Williams Protective & Marine and based in Minneapolis, Minnesota. With approximately 20 years of experience in the coatings and chemical industry – both as an educator and a Sherwin-Williams team member – he has specialized in multiple subject matters related to corrosion, coatings performance, asset protection, and coating solutions for the renewable energy sector. Contact: jigar.mistry@sherwin.com.

Neil Wilds is the Global Product Director – CUI for Sherwin-Williams Protective & Marine. With 37 years of technical coatings experience, Wilds develops strategies for long-term asset protection and directs the development of specifications and testing programs. He is a member of several coatings associations including AMPP, NORSOK M501, the International Organization for Standardization (ISO) and others. Contact: neil.wilds@sherwin.com

THE SHERWIN-WILLIAMS DIFFERENCE

Sherwin-Williams Protective & Marine delivers world-class industry subject-matter expertise, unparalleled technical and specification service, and unmatched regional commercial team support to our customers around the globe. Our broad portfolio of high-performance coatings and systems that excel at combating corrosion helps customers achieve smarter, time-tested asset protection. We serve a wide array of markets across our rapidly growing international distribution footprint, including Energy, Water & Wastewater, Bridge & Highway, Steel Fabrication, Flooring, Manufacturing & Processing, Fire Protection, Marine, Rail and Power.