Fatigue loading on subsea monopiles used within wells has been an increasing problem in recent years for the oil and gas industry through the use of larger and heavier equipment on the monopole, longer operating durations and harsher environments. However, this is not a unique problem to the oil and gas industry as wind turbine monopiles also face large cyclic loading over extended life times. This challenge has prompted the widespread implementation of monitoring systems to confirm predictions of monopile loading and fatigue and ensure that: operations are conducted safely, inspection regimes may be properly specified; and life extension may be possible.
Monitoring system design requirements, data processing and evaluation of field measurements from a number of offshore monopiles are described. Monitoring systems for measurement of monopole fatigue require careful planning to ensure adequate quality of the data and cost effectiveness. The evaluation will determine the suitability of off-the-shelf equipment or the need for application specific devices. An example assessment of the requirements of measurement devices from which monopile fatigue can be derived is given that demonstrates the importance of integrated consideration of instruments, resolution and data processing methods in the selection and design of the system. Conservatisms in monopile design may be removed by using continued monitoring to increase understanding of these systems. Premature failures may be prevented through better understanding of the system loading and extension of the operating life of monopole foundations is shown to be possible.
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