ABSTRACT
During inspection of a monotower a large crack (about 1 m in length) was discovered along the weld toe of a tubular joint. This location had not been inspected in the first 13 years of the life time due to the very low calculated fatigue damage and stress level. Investigations were made including: vortex shedding, installation damage, etc. But none were satisfactory. The calculations of the jacket structure were then studied in more detail but those were not able to capture the local effect relevant for this detail. Furthermore, since the member was connected to a pile sleeve, the stiffness of the sleeve was overestimated. A detailed local model including the sleeve, the grout, the pile and using gap elements between sleeve and grout was developed, and a non-linear fatigue analysis was carried out. The results show a damage life of 4–6 years, also well correlated to the facts.
