Abstract: This paper presents an analysis of the cracking causes in a wind tower of a wind farm. The cracks were detected in several towers of the farm, in the welded joint between the lower ring of the towers and the flange connecting the towers to their corresponding foundation. In the extreme case, here analysed, the crack was a through thickness crack. In order to clarify the cracking causes, the component was inspected in situ, non-destructive tests were performed on the base material, the weld bead and the Heat Affected Zone (HAZ), and a Finite Elements (FE) simulation was carried out to determine the stress state in the welded joints and to develop the corresponding fatigue analysis following the Fatigue Module (Chapter 7) of the FITNET FFS Procedure. The analysis has demonstrated that the main cause of the cracking process is an inadequate design of the joint, with high stress concentrations and an insufficient resistant section on the flange. Finally, two tentative solutions (grinding and grinding plus soft transition) have been analysed but none of them have provided satisfactory results.

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