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Welding How Welding Consumables Extend the Service Life of Offshore Towers

From Martin Hübner | Translated by AI 2 min Reading Time

Welded seams are among the most stressed areas of offshore wind turbines. Researchers at BAM have now shown that special welding consumables can increase their fatigue strength by 50 to 140 percent compared to conventional welds.

Special alloys, so-called low transformation temperature filler materials (LTT), change the structure of the weld seam during cooling in such a way that residual tensile stresses are significantly reduced.(Image: Image)
Special alloys, so-called low transformation temperature filler materials (LTT), change the structure of the weld seam during cooling in such a way that residual tensile stresses are significantly reduced.
(Image: Image)

Offshore wind turbines consist of numerous welded individual parts and are exposed to extreme loads from wind and waves. These lead to cyclical stresses that particularly affect the weld seams. Until now, they have been considered a critical factor, particularly in the case of high-strength steels, as the welding process changes the material structure and generates damaging residual tensile stresses. For safety reasons, the relevant regulations have so far only allowed the lightweight construction potential of these steels to be exploited to a limited extent.

Significantly Reduce Residual Tensile Stresses

As part of a cooperation project coordinated by the Federal Institute for Materials Research and Testing (BAM), new types of welding filler materials, known as low-transformation temperature (LTT) filler materials, were therefore investigated. These special alloys change the microstructure of the weld seam during cooling in such a way that residual tensile stresses are significantly reduced. In some cases, they even create favorable residual compressive stresses that counteract the formation of fatigue cracks.

In offshore wind turbines in particular, the fatigue strength of the weld seams is crucial to the service life.

Martin Hübner, author of the study from the Wind@BAM competence center

Typical high-strength steel components with additional structural reinforcement, such as those used in towers and support structures of wind turbines, were investigated. These parts are among the most heavily stressed components in such systems. Depending on the design and seam geometry, the fatigue strength could be increased by 50 to 140 percent compared to conventional welds. An additional, specifically placed LTT welding layer in the highly stressed seam area proved to be particularly effective.

"Especially in offshore wind turbines, the fatigue strength of the weld seams is decisive for the service life," explains Martin Hübner, author of the study from the Wind@BAM competence center. "Our results show a potential for the safe realization of higher loads and larger turbines—without time-consuming and cost-intensive post-treatment processes."

Additional Work Steps Can Be Omitted

A key advantage of the concept is that the desired effect is created directly during welding. Additional work steps are not required, which makes its use particularly attractive for industry. In the future, the targeted use of LTT filler materials will also open up opportunities for repairing and upgrading existing weld seams.

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