A Study of Fatigue Crack growth in Offshore Wind Monopile Parent Steel in Air and Seawater

Abstract

Offshore wind turbines supported on monopile structures have significantly different structural dynamic response characteristics compared to oil and gas structures due to the structural stiffness and machine loading characteristics. Therefore, the effect of corrosion assisted fatigue damage in offshore wind turbine support structures needs to be researched and better understood for reliable operation of the structures in service. This paper presents constant amplitude fatigue crack propagation tests conducted on representative Compact Tension specimens (CT) in air and in laboratory simulated free corrosion seawater environment similar to what might be experienced by steel monopile wind turbine support structures. Crack growth rates were shown to be faster in seawater than in air across all the applied cyclic stress intensity factor ranges tested. Mean stress effect on fatigue crack growth was accounted for at stress ratios of -1 to 0.6 using various mean stress models. Significant difference in the predicted results is discussed