Measurement of Weld Depressions in Thin-walled Steel Tubes before and after Circumferential Welding

Thin-walled circular steel tubes are a widely-used structural element for wind turbine towers. An important limit state for these tubes is local buckling of the tube wall in compression and the strength of this limit state is sensitive to geometric imperfections, which are sensitive to the fabrication process. Wind turbine tower sections are usually manufactured by can-welding, where flat steel plates are rolled into cylinders and seam-welded into ""cans,"" fit to adjacent cans by tack welding along the circumference between cans, and fully connected with a continuous circumferential weld. A well-known imperfection induced by this process is the weld depression, a radially inward axisymmetric deviation formed during the cooling of the circumferential weld. These depressions have an important influence on the structural behavior of thin-walled tubes, so it is meaningful to understand the evolution of this imperfection pattern during the fabrication process. Using the latest noncontact laser-scanning instrumentation, full-field measurements are used in this paper to capture the change in geometric imperfections of two can-welded tubes before and after full circumferential welding. The two tube sections have diameter D equal to 1003 mm and thickness t equal to 4.8 mm, corresponding to a diameter-to-thickness ratio D/t equal to 211. These tubes are roughly a 1:4 scale model of a wind turbine tower section. Geometric imperfections of these tubes, defined as radial deviations between the measured geometry and the nominal geometry based on drawings, are presented and compared. Weld depression profiles of the measured geometry before and after circumferential welding are isolated and compared.

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