Producing large wind towers at lower cost
Flanges, for which there are few manufacturers worldwide, are currently forged, making them expensive and time consuming to produce. Producing them via a different method requires new techniques and an improved process understanding. The EU-funded 'Offshore wind turbine towers – A quicker, cheaper flange supply route' (RINGMAN) project was set up to develop an alternative manufacturing route using cold-rolled plate metal. To achieve this, a new electron beam (EB) gun and welder as well as new quality and safety standards for fabricated flanges were required. As guidelines had been drawn for forged flanges, researchers developed models for better understanding the flange stresses and fatigue performance prior to their fabrication. Researchers used them to set an acceptable quality threshold for defect size in the fabricated flanges. RINGMAN partners used a reduced-pressure EB welding process for joining the ends of the rolled rectangular section rings made of carbon–manganese steel. The required EB equipment to achieve fast and reliable thick flange welds produced beam power up to 60 kW. Requiring no filler material, it completed 130-mm welds at a single pass at a welding speed of 100 mm/min. A post-weld heat treatment procedure was developed to restore the metal microstructure, producing a fine-grained microstructure that was indistinguishable from the base material. To detect the size of critical flaws in different regions of the flange section, researchers used a combination of surface flaw detection and ultrasonic testing methods. The demonstrator flange component was inspected to determine the weld quality. The EB welding technology, the post-weld heat treatment and the machined flange element all met the requirements set in the acceptance criteria report. RINGMAN's flange fabrication process promises to lower the production cost of these wind turbine parts. This should also serve to promote European competitiveness in the global wind turbine industry.
Keywords
Wind turbine tower, flanges, cold-rolled plate metal, electron beam
