Influence of pitting corrosion on the fatigue strength of offshore steel structures based on 3D surface scans

Abstract

Support structures for offshore wind turbines and the corresponding transformer platforms are highly susceptible to corrosion. In particular, the phenomenon of pitting is crucial, as it leads to local stress concentrations and thus affects the fatigue life of structures. Despite corrosion protection systems, corrosion cannot be completely avoided, which can lead to pitting corrosion on the steel surface. This leads to fatigue life reduction, since the structures are exposed to high dynamic loads. Local stress concentrations can be considered in local concepts but so far, corrosion effects in local concepts are insufficiently defined. Hence, this paper aims to investigate the impact of pitting corrosion and the corresponding stress concentration on the fatigue life endurance of structural steel, used for offshore wind support structures. For this purpose, a total of 36 pre-corroded specimens with pitting were tested against fatigue failure and monitored with Digital Image Correlation. In addition, the specimens were scanned with a high-resolution 3D scanner and converted to numerical models by reverse engineering, to determine the stress concentrations on the surface. In most cases the hotspots from the numerical model coincide with the crack location detected with Digital Image Correlation. The notch effect has a significant impact on the crack location and crack path.