1st Mai 2021: Salzgitter Mannesmann Renewables GmbH joins SmartWeld Project
This project aims to reduce the carbon emission of offshore steel Jackets during fabrication, transport (and installation) through overall substructure weight reduction. Since the overall Jacket weight is highly driven by the steel node dimension, which is mainly determined by the fatigue resistance of the node, this project focus on improving the fatigue resistance by innovative lightweight design approaches including principles of bionic design, notch stress approach and fracture mechanics. Also, the prove of producibility of optimized node design (i.e. weld shape) by means of robotic welding technologies and the prove of fatigue life extension utilizing small, medium and full-scale fatigue tests are main targets.
Approach
Following the notch stress approach and hence the assumption that the node fatigue life is driven by the local stress situation at the weld, the weld geometry (notch radii, weld flank angle and weld shape) will be modified by bionic design principles utilizing FE simulations such that an minimized notch stress is gained. In order to compute the life time the classical structural stresses approach as well as a combination of notch stress concept and fracture mechanics is applied.
Subsequent small scale nodes (1:3.3) and medium scale nodes (1:1.5) with conventional and optimized weld shape will be produced and fatigue tested in order to confirm optimisation potentials. The fatigues test program is designed to create a Wöhler curves for both small scale nodes and medium scale nodes (i.e. each will have at least 16 specimens) and, therefore, enable to determine to optimisation potential with respect to the DNVGL specifications. Implying that only automated welding procedures enable to model the weld shape as required in terms of quality and reproducibility all nodes will be manufactured by means of robotic welding technologies, apart from some manual welded nodes as reference. In addition to the investigation of local stress / geometry interaction the overall geometry of nodes, i.e. misalignment, ovality and wall thickness variations will be measured too and implemented in the FE models to examine its impact on fatigue life. Furthermore, fracture mechanic analyses of crack development and growth are planned to investigate to full potential of optimized weld shape.
In order to rise the industrial acceptance of gained improvements through weld shape optimisation three full scale nodes (chord 1219 mm, 50 mm / stub 610, 25 mm wt.) will be manufactured by means of robotic welding and fatigue tested by Federal institute for material research and testing (BAM).
Based on the computed lifetime extension for nodes and subsequent for the whole Jacket the weight reduction potentials will be calculated and reflected to potential CO2 emission reduction during steel making and steel processing.
Project basics
- Project name: smartweld
- Public funded by Federal Ministry for Economic Affairs and Energy with 2,6 Mio. €
- University partners: Leibnitz University of Hannover, BAM-Federal institute for material research and testing, Fraunhofer IWES,
- Industry partner: JBO (designer), Salzgitter Mannesmann Renewables / Salzgitter Mannesmann Forschung (robotic welding of full scale nodes)
- Associated partner: certification bodies, developer, designer
- Project start: 1.05.2021
- Duration: 3 years