KIT Steel and Lightweight Structures

Increasing the Strength and Durability of Bonded Steel Joints in Offshore Applications (P 1393)

  • contact:

    Jakob Boretzki, M.Sc., Dr.-Ing. Matthias Albiez

  • project group:

    Adhesive bonding and joining technology

  • funding:

    FOSTA, AiF

  • Partner:

    Fraunhofer Institute for Large Structures in Production Engineering IGP, Rostock

    Fraunhofer Institute for Manufacturing Technology and Applied Materials Research, Bremen

  • startdate:

    2019 - 2022

Offshore-WEAKIT Stahl- und Leichtbau

Offshore wind turbines have, in addition to the main components tower, nacelle and rotor blade, numerous other secondary structures such as boat landings, platforms, cable protection tubes (J-tubes), etc., which are connected to the primary support structure by structural steel (usually welded or bolted) connections. Furthermore, there are connections of much smaller dimensions such as cable and lighting supports or supports for corrosion protection systems.

Offshore wind energy is a young and dynamic industry. New technologies are regularly developed and tested, so that many of the structures built are unique and the support structures can vary from wind farm to wind farm. Due to this high dynamic in structure design, retrofitting of the aforementioned attachments in the field is a frequent occurrence. Damage cases also require suitable repair concepts under harsh offshore conditions.

The problem with the joining methods used is that they damage the basic structure. The bolting or welding joining methods introduce geometric or metallurgical notches. These lead to a downgrading of the notch class and thus to reduced fatigue strength. If the attachment of secondary structures by the joining methods mentioned is planned, this must already be taken into account in the dimensioning of the primary structure. An increase in wall thickness necessitated by this leads to reduced resource efficiency. Structures, that are subsequently attached offshore, often lead to the fact that the fatigue check can no longer be fulfilled and the calculated service life can no longer be achieved. In addition, the corrosion protection is locally destroyed by the attachment. In summary, there is a great need for a solution to connect secondary components without damaging the base material.

The aim of the research project is to systematically investigate an adhesive bonding of secondary structures to the primary structure. Bonding is not associated with any damage to the primary structure. Neither does high heat exposure occur, nor does the basic structure have to be weakened by screw holes. Adhesive bonding is carried out between face plates, which are attached to the secondary structure, and the primary structure. Both adhesive bonding in the factory and offshore bonding and subsequent use under offshore conditions are to be mapped by means of tests.

In detail, the following focal points will be investigated:

  • Selection and characterization of suitable adhesives and coating systems
  • Development and testing of manufacturing concepts for offshore applications (surface treatment, injection, rapid curing)
  • Investigations on aging both under outdoor weathering and in the laboratory under standardized environmental conditions
  • Development, optimization and experimental investigations of component-like sample