Investigation of the effect of pitting corrosion on the fatigue strength degradation of structural steel using a short crack model

Steel support structures of offshore wind turbines (jackets and monopiles) undergo both fatigue and corrosion damage, impacting their lifetime. This paper investigates how pitting corrosion, caused by being exposed to the marine environment, affects the fatigue strength of structural steel. A short fatigue crack model is used to estimate the minimum required applied load amplitude which causes a growing crack emanating from the bottom of a semi-elliptical pit. Pit growth rate data, reported in literature, is employed to update the pit size and its sharpness at each time step. The modelling results show the fatigue strength degradation as a function of the exposure time to the corrosive environment. As exposure time increases, it is observed that degradation happens more quickly in the early years followed by a gradually decreasing degradation rate of the fatigue strength in the following years.