Abstract
Offshore wind turbines (OWT) are a major goal of the energy strategy of Germany encompassing the increase of the installed wind power. OWT components are manufactured from welded steel plates with thicknesses up to 200 mm. The underlying standards and technical recommendations for construction of OWTs encompass specifications of so-called minimum waiting time (MWT) before non-destructive testing of the weld joints is allowed. Reason is the increased risk of time-delayed hydrogen-assisted cold cracking as hydrogen diffusion is very slow due to the very thick plates. The strict consideration of those long MWT up to 48 h during the construction of OWTs leads to significant financial burden (like disproportionately high costs for installer ships as well as storage problems (onshore)). In this study, weld joints made of S355 ML were examined in comparison with the offshore steel grade S460 G2+M. The aim was to optimize, i.e., reduce, the MWT before NDT considering varied heat input, hydrogen concentration and using self-restraint weld tests. This would significantly reduce the manufacturing time and costs of OWT construction. To quantify the necessary delay time until hydrogen-assisted cold cracks appear, acoustic emission analysis was applied directly after welding for at least 48 h.
Highlights
1.1 Welding and waiting time before non-destructive testing (NDT)For the aim of increasing the renewable energy generation, many offshore wind turbines (OWT) will have to be installed (20 GW wind power till the year 2030) [1, 2]
The test welds performed with M21 gas show a diffusible hydrogen concentration of 1.8 to 3 ml/100 g Fe for both filler materials, i.e., reduced HD class to avoid hydrogen-assisted cold cracking (HACC)
The fact that free shrinking samples (FSS) with low restraint intensities (RFy − 0 kN/(mm × mm)) show crack relevant acoustic emission (AE) signals and they appear for low-HD experiments. These results show increasingly that NDT and metallographic analysis is important for a validation of the AE results and to give a statement on the minimum waiting time (MWT)
Summary
1.1 Welding and waiting time before NDTFor the aim of increasing the renewable energy generation, many offshore wind turbines (OWT) will have to be installed (20 GW wind power till the year 2030) [1, 2]. Most OWT components demand excessive welding fabrication of components of structural steels and especially. The standards for construction of OWTs do not differentiate sufficiently the available offshore steel grades [5]. Advanced thermomechanical rolled offshore steel grades like the S460 G2+M [9] offer an improved weldability due to the reduced carbon equivalent combined with excellent mechanical properties [10]. These steels can be welded with reduced heat input, without preheating and have an increased resistance against HACC [10, 12, 13].
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call