A Bandage for the Post

Researchers: Veronika Eggert, Dr. Mohammad Fazel, Saeid Sarafrazian, Maren Seidelmann, Prof. Dr.-Ing. habil. Marcus Rutner

A four-member, interdisciplinary team is working on an ultra-thin coating that could revolutionize steel construction. This “nano bandage” made of nickel and copper can multiply the lifespan of offshore wind farms, among other structures. The project combines fundamental research with high practical relevance.

In Germany, there are nearly 40,000 bridges with a total length of over 2,000 kilometers—many made of steel or containing steel components. In addition, there are about 30,000 onshore wind turbines and around 1,600 offshore in the North and Baltic Seas. Wind and waves, temperature fluctuations, and vibrations expose the material to cyclic loads over decades. At fatigue-critical points, often along weld seams, tiny local cracks form. Over time, they grow until the structure must be repaired or replaced. In Germany, such cases have accumulated into a multibillion-euro maintenance backlog.

At Hamburg University of Technology (TUHH), an interdisciplinary, international team led by Prof. Marcus Rutner, head of the Institute of Metal and Composite Construction, is developing an ultra-thin coating that could multiply the durability of welded joints.

Nano Bandage for Steel

“We coat the surface with a multilayer of nickel and copper layers, each only a few nanometers thick,” explains materials scientist Saeid Sarafrazian - one nanometer is a billionth of a meter. The “nano bandage” consists of alternating hard nickel layers and softer copper layers. Each double layer is about 50 nanometers thick, resulting in a total coating just a few micrometers thick, applied precisely to fatigue-critical areas along weld seams. Structural engineer Veronika Eggert uses numerical models to determine the optimal procedure.

“The welded joint is often the most critical part of a steel structure,” explains structural engineer Maren Seidelmann. “Different stresses, material structures, and geometries converge here. Cracks almost always start at the weld.” Seidelmann is currently developing a method to apply the nano bandage directly on existing structures: “We can bring the electrolyte solution to the desired location in a container and apply the coating galvanically on-site.”

Pressure Against Cracks

Laboratory tests have shown the process to be remarkably effective. For structural steel samples, the researchers found a three- to sixfold increase in lifespan compared to untreated welds. “We demonstrated the effect on standardized samples and also showed that the variability of results is lower than with other methods,” says Mohammad Fazel, the second materials scientist on the team. “This means the technology is not only powerful but also reliable.”
The findings come not only from traditional fatigue tests but also from visual analyses with electron microscopy. These have also helped clarify the mechanism behind the nano bandage.

Four Effects Provide Protection

The exceptional durability results from the interaction of several mechanisms, as confirmed by measurements at the Deutsches Elektronen-Synchrotron (DESY):

1. Residual compressive stresses in the steel beneath the coating counteract tensile stresses and suppress crack formation.
2. Surface roughness is greatly reduced by the electroplated coating, eliminating potential notches.
3. The coating suppresses slip bands—tiny zones of plastic deformation on the surface that can otherwise become crack initiation points.
4. Within the nanolaminate itself, crack deflection and multi-cracking delay crack propagation.

From Millimeter to Meter

So far, the team has coated standardized samples eight millimeters thick. The next step is to scale the process to large structural components. “We want to demonstrate that the method also works for 80-millimeter-thick offshore structures,” says Sarafrazian. The tests use nearly two-meter-long samples weighing 360 kilograms. Such dimensions are typical for monopiles - the massive steel tube foundations of wind turbines. They can have circumferences of up to 30 meters and are particularly vulnerable at their ring-shaped weld seams.

Offshore wind farms face extreme conditions: not only mechanical stresses but also saltwater corrosion. Wind turbines typically have a lifespan of only 25 years. Thus, the need for life-extension measures is greatest here. Maintenance and repair costs are a major issue, compounded by a shortage of skilled labor. Every additional year of operation beyond the original service life significantly eases the transition to renewable energy.

If a bridge could last 150, 200, or even 400 to 500 years instead of just 100, this would save not only vast sums of money but also huge amounts of energy - showcasing resource efficiency at its best.

Less Steel, Longer Life

A calculation for a 15-megawatt wind turbine illustrates the effect. If all the ring-shaped weld seams of a monopile were treated with nanolaminates, the structure could be made 28% lighter, since the fatigue sensitivity of the welds would no longer dictate the design. At the same time, the system’s lifespan could increase by a factor of three to six.

This means less material consumption and a significantly smaller CO₂ footprint in both production and maintenance - a crucial lever for climate protection. After all, the global steel industry accounts for about 8% of worldwide CO₂ emissions.

The goal is to certify the process so that it can be transferred into industrial use. “We want to contribute to making steel construction more sustainable,” says Rutner. “If we can reliably and cost-effectively protect fatigue-critical points with a nano bandage and extend the life of structures, it would be a paradigm shift in offshore and civil engineering - essentially, Engineering to Face Climate Change.”

Info

The three-year project is funded by the Federal Ministry for Economic Affairs and Energy with €2.2 million. Project partners include the monopile manufacturer Steelwind Nordenham, the JBO Engineering Group, and the Federal Institute for Materials Research and Testing (BAM). Associated partners include AG der Dillinger Hüttenwerke, Salzgitter Mannesmann Forschung, Siemens Gamesa Renewable Energy, Vestas Wind Systems, EnBW, RWE, and TÜV Süd.

Publications have already appeared in Scientific Reports, Scripta Materialia, and Stahlbau.