Fatigue strength degradation of structural steel in sea environment due to pitting corrosion

Steel support structures of offshore wind turbines (jackets and monopiles) undergo both fatigue and corrosion damage, impacting their lifetime. Due to the time‐variant uncertainties associated with environmental and mechanical loads, having reliable models that allow prediction of the degradation due to corrosion and fatigue is necessary to accurately assess the structural integrity and to support decision-making. This work investigates how pitting corrosion, caused by being exposed to the marine environment, affects the fatigue strength of structural steel. A short 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. The modeling 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 convergence of the fatigue strength to a minimum value. ALso, a parametric study is done to see the effect of the pit size and sharpness of the degradation of the fatigue strength. It illustrates that for a specific pit sharpness by increasing the pit size the fatgiue strength decreases sharply at first and then tends to converge to a specific value which depends on the sharpness of the pit