Abstract

Electron beam (EB) welding has high productivity and can weld steel plates with a thickness of more than 50 mm (Onoue, 1985). However, in general, securing the toughness of a weld joint is difficult. To deal with the above issue, the technology to refine a microstructure was applied to the weld metal (WM). It was comfirmed that the formation of intragranular ferrite and optimized Ni addition to the groove of an EB weld joint were important for improving the low-temperature toughness. Based on the above-mentioned technologies, it was demonstrated that the newly developed EN10025–4 class steel plates had excellent toughness in the EB weld joint.

Introduction

The current trend in offshore wind energy is towards larger wind turbines because of the economics of installation and operation. For this reason, heavy steel plates are applied to these large structures and there is increasing interest in innovative welding technologies for cost-efficiency and high productivity.

There seems to be two candidate solutions of welding technologies to increase the productivity. One solution is to increase the productivity of arc welding by applying high-speed welding (Gehring, 2008) and high-heat-input welding (Homma, Hoshino, Nakashima, Shishibori, Kojima, Nishimura and Bockelmann, 2013).

Another solution is to apply alternate welding technology with high productivity. EB welding has high productivity for welding steel plates. Heavy steel plates with a thickness of more than 100 mm can be welded by a single pass of EB welding; however, there are issues with applying EB welding to the manufacture of offshore wind foundations. A huge vacuum chamber is required to weld a large structure such as a 40 m long monopile for an offshore wind turbine, because EB only can be generated in high vacuum (10-2 Pa).

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