Estimation of the maximum allowable lack of penetration defects in circumferential butt welds of structural tubular towers

This paper analyses the structural integrity of structural tubular towers (i.e., towers of wind turbines and floodlight towers) with lack of penetration defects on their circumferential butt welds. The methodology presented is particularised to the analysis of the lack of penetration defects detected in certain sections of several wind towers after the construction process. It is also analysed how such defects affect the fitness for service of the towers during their theoretical lifespan (20 years). The methodology (based on the use of Failure Assessment Diagrams, FAD) can easily be extrapolated to the assessment of other types of defects or towers. Its main hypotheses consist of establishing that the defects behave as internal cracks with certain geometries and also that fracture and fatigue are the key processes affecting the structural integrity of the towers. Then, the resulting allowable crack size, corresponding to the lifespan of the tower, for the different sections analysed and for the different crack geometries considered is determined.