Addressing Offshore Wind Structure Challenges

The offshore wind energy industry has seen enormous growth in recent years, and it doesn’t look to be slowing down anytime soon. Those in the industry will know the stats: the offshore wind energy market is forecast to reach $42 billion by 2025, with a projected compound annual growth rate of 13.6% from 2020 to 2025.

Evidence of the increased focus on achieving clean, renewable energy can be seen worldwide. A skim through renewable energy news sites reveals new projects being commissioned on an almost weekly basis. In January, U.S. President Joe Biden signed an Executive Order that includes doubling offshore wind power generation in U.S federal waters by 2030, and his recent infrastructure plans include considerable attention to green energy sources. In October of last year, the United Kingdom government—already home to the largest offshore wind market in the world—announced a £160 million injection into the industry to upgrade ports and infrastructure. Vietnam has big plans to increase its proportion of power from wind and solar from 10% in 2019 to 42% of its national grid by 2045. Although most current locations are onshore, the country is already making great strides to achieve that goal ahead of schedule, with the next big push in offshore wind off its southern coast. With that progress, of course, comes the need for preventative maintenance and protection.

This push for increased offshore wind energy takes advantage of the power of the wind produced at sea, moving at a much higher and more consistent speed thanks to the open space and absence of structures. What is a benefit to production, however, poses a logistical disadvantage to construction and maintenance along with an aggressive corrosive environment. While many offshore installations are currently situated near the shore in predominantly shallow waters, the next few years will see a move to deep water installations further away from the coast, as space becomes an issue. These developments will see stronger winds and bigger waves, adding pressure to not just the installation phase, but ongoing operation and maintenance.

On an offshore wind turbine structure, corrosion can occur in many different areas—monopiles, ladders, walkways, boat landings, guard rails and rotor heads—and compromise the overall integrity of the structure. Coatings systems have been applied to protect wind structures from the intense offshore environment for decades, and both coating manufacturers and industry standardization organizations have made recent strides in bringing new technologies to the market to meet this growing demand for corrosion protection. However, performing maintenance coating offshore can require ex-tensive equipment, supplies and manpower to perform the surface preparation and application—all of which need to be transported offshore, which presents its own logistical challenges.

Currently, other complications add to these challenges and further threaten progress in the sector. No one could have imagined how 2020 unfolded, with a pandemic sweeping the globe, many countries in recession, budgets being hit harder than ever. Oil prices dropped, projects were put on hold, struggles with supply chains surfaced, workforce constraints and social distancing measures were imposed, and turn-around projects were pushed back with just a focus on the critical work required. Even as the pandemic has subsided in some areas, many in the industry report ongoing challenges in hiring and retaining skilled workers.

The impact of these challenges on maintenance and asset integrity is profound, and maintenance man-agers now face a whole new set of challenges to balance on an already sensitive set of scales. Deployment of maintenance personnel has, and will likely continue, to be a challenge for 2021—not only with the risk of an outbreak among staff, but with the need to provide a safe environment with social distancing measures and PPE equipment while vaccines are rolled out. This has resulted in smaller workforces in operation at any one time and careful deployment to where manpower is needed most, delaying operational and maintenance activities. Reductions in workforce allowed at any one time to comply with these measures will likely slow further production.
Ongoing constraints on travel across the globe pose additional problems for the movement of personnel to get to project destinations whether it be inspection or maintenance activities. Quarantine times and isolation windows could well extend the time people are travelling, and of course whether countries have agreed air bridges to enable the reciprocal flow of passengers.

While the industry faces constraints to operational maintenance, there is one universal truth: the work still needs to get done. This is where minimal footprint solutions, which require the least amount of personnel and equipment to complete the work, can potentially present an advantage.

This article will discuss two potential corrosion protection materials that can be used to protect offshore wind structures using minimal manpower and surface preparation and application equipment, potentially offering benefits in maintenance time, long-term protection and costs.

Surface Prep Footprints

The subject of surface preparation is always an interesting one when it comes to corrosion. While abrasive blasting is effective, it is also a messy undertaking; work areas need to be protected, waste must be contained and disposed of, the by-products can be hazardous, and it takes consider-able time and skilled manpower. Surface preparation is a key step in any corrosion prevention coating, but if preparation of a structure can be managed to the point where it can be performed in a simpler fashion than abrasive blasting—such as using a wire brush or other hand tool—it can be a huge advantage to operational maintenance time.

If extensive corrosion is identified on on an offshore structure, materials and equipment will need to be brought offshore to work on the piece onsite. This will likely include large, heavy surface preparation and coating and application equipment, as well as access equipment, personal protective equipment and other materials and supplies. Once the job is complete, all equipment must be transported back. Any waste generated during surface prep and coating operations must be segregated and disposed of properly.
However, if only small areas of corrosion are identified on an offshore wind turbine structure, less demanding options might work.

Polymeric Patch

A polymeric coating was recently developed based on the idea that a corrosion solution could be applied simply as an adhesive patch rather than painting or spraying. This corrosion preventive patch is designed for single-layer application for touch-up and spot-repair of existing coating systems, as well as an environmentally and worker-safe alternative to traditional coating systems for atmospheric offshore applications. These 100%-solids viscoelastic polymer patches contain no VOCs and can be applied after minimal surface preparation, such as to SSPC-SP 1, Solvent Cleaning, or SSPC-SP 2 and SP 3, Hand and Power Tool Cleaning, without a required surface profile for adhesion. At a nominal thickness of 40 mils, the patches can be applied at temperatures ranging from 14 to 120 F, and reportedly withstand cyclic aging testing according to ISO 20340.

For instance, one individual, or a small team, could potentially head to the site armed with a wire brush and an alternate corrosion protection method, such as a roll of patches. They can brush the loose corrosion away, apply a protective patch and return with only the release liner and cardboard as waste. Each corrosion spot can potentially be halted from expansion as soon as it is observed, allowing the operator to avoid reaching the point of blasting, removing chlorides and repainting the structure until the end of its design life—which, depending on time in-situ, could be up to 30 years.

Any void or exposed groove on an offshore structure is a vulnerable spot for crevice corrosion that may affect the integrity of the structure. Transition pieces are one of these examples: close to the sea and with high chloride content accumulation, and prone to accelerated corrosion and threatened integrity. Applying the self-adhesive corrosion preventative patch over the groove can seal it off from the environment and prevent corrosion formation. For example, the patch can be applied to the groove of a transition piece; in this case, the coated transition pieces and the applied polymeric coating tape combine to give added corrosion protection to the piece.

Another area that can potentially benefit from that extra protection are flanged structure connections. Flanged spots not only contain voids that accumulate unfavourable environmental impacts that can threaten the protection of the asset, but also expose a lot of sharp angles, like bolts and nuts, prone to damage during installation as well as during service life of the structure. By encapsulating the flange using a polymeric paste, basecoat and an addition of extra mechanical protection layer such as composite wraps, maintenance operators can not only prevent corrosion, but also potentially increase the mechanical properties of what would otherwise be considered a weak spot of the structure.

Thermoplastic Coating

There are many situations that require the ability to remove the existing protective coating for maintenance while the structure is in service, such as during addition of new structural bolting, welding or steel repairs, or simply when moving different parts of the structure. Take, for instance, performing maintenance on a working crane pivot, hydraulic fitting or actuator—these items might all be coated or otherwise maintained during normal operational use instead of requiring a production shutdown, which can obviously present a huge benefit for operators.

Another recently developed thermoplastic coating solution has been put to the test in the challenging environment in which wind turbine structures operate. This organic polymeric resin coating can be applied in a fluid state to penetrate threaded fastenings and protect these critical areas from corrosion spread. Additionally, the coating can be applied in-service at elevated surface temperatures, allowing equipment to remain operational during application. Due to the viscoelastic behaviour of the solution, it has the ability to withstand expansion and contraction of steel without cracking or loss of adhesion.

Again, required surface preparation is minimal; solvent cleaning and wire brushing is sufficient to clean the area, so no blasting is required. The coating can be applied in humid conditions at surface temperatures between 41 and 158 F. The coating reportedly withstands ISO 20340 and ISO 2812 accelerated weathering and submersion tests, among others.

While the ability to easily remove the coating is a notable benefit, non-destructive testing and inspection can be achieved without removal of the coating during scheduled maintenance. These features, combined with the ability to apply the protective coating without a shutdown in operations can potentially keep costs and project timelines in line. The coating is reported to have been successfully applied on multiple offshore wind structures and oil platforms, ships, as well as other heavy duty industrial structures.

Conclusion

The need for optimized corrosion maintenance on offshore wind structures has never been clearer, as renewable energy production continues to gain steam worldwide, and ongoing pandemic-related workforce and transportation issues make performing maintenance work all the more challenging.
The rehabilitation options covered in this article certainly aid corrosion maintenance work in less time with fewer maintenance personnel deployed. They also highlight just how innovation is leading to smaller and more agile solutions for complex corrosion issues.  JPCL

By Somaieh Salehpour

Somaieh Salehpour is the Vice President, Technology and Strategic Marketing for Seal for Life Industries. She has more than 10 years of industry experience and holds a B.S. in polymer engineering and science from Amirkabir University of Technology/Tehran Polytechnic and an M.A.Sc and PhD in chemical and biological engineering from the University of Ottawa.