ABSTRACT
Offshore wind turbine monopile structures are fabricated from rolled steel plates welded both longitudinally and by circumferential or splice welding processes. In spite of the level of quality control measures applied during fabrication and welding, there is still the potential for defects at the intersection between the parent material and the weld region which could result in some significant local stress concentrations. Due to the synergistic effects of a corrosive environment, machine, wind and wave loading encountered by the structures in service, fatigue cracks can initiate from the weld region and propagate progressively to failure. Fatigue cracks in offshore wind farm monopiles therefore need to be discovered and sized by reliable inspection and monitoring techniques to ensure economical and safe operation of the structures.
