Probabilistic modelling of pitting corrosion and its impact on stress concentrations in steel structures in the offshore wind energy

Supporting structures for offshore wind turbines and the appropriate transformer platforms are highly susceptible to corrosion. Especially the phenomenon of pitting corrosion is very crucial, since this leads to local stress concentrations and hence has an impact on the fatigue life of marine structures. Despite corrosion protection systems, corrosion cannot be completely avoided, which can lead to pitting corrosion on the steel surface. Stress concentrations from pitting corrosion are not explicitly considered within the design of offshore structures. This is only possible by using local fatigue concepts, which requires a realistic modelling of corroded steel surfaces and the corresponding stress concentrations. Hence, in this work, three different models for evaluating the stress concentrations were developed: single-pit model, double-pit model and random fields model. The results were compared to the stress concentrations of a real corroded surface, which was analysed with the reverse engineering method. In all models, the probability-based determination of the stress concentration was the main focus in order to consider the characteristic scatter in pitting corrosion. The comparison of the three models with the real surface shows a good agreement with the double-pit model. It becomes evident, that the single-pit and the random fields model are not sufficient for modelling the stress concentrations. However, derived stress concentrations from the double-pit model and the real surface model can be utilized for risk and reliability-based analysis with local fatigue strength concepts.