In offshore windfarms there has recently been an increasing trend in the use of large diameter bolted connections for the connection between the Transition Piece (TP) and the Monopile (MP). The dimensions of such connections cause handling challenges due the size of the bolts, often M72. An cost driver for these connections the need for maintenance: neither the maintenance intervals nor the maintenance scope can be clearly deferred from standards, and industry experience specifically on these large diameter flanges is generally limited. For these offshore installations, maintenance costs and HSE risks can be high due to the difficult accessibility of these bolted connections offshore often in confined spaces. I n addition, maintenance periods should preferably be scheduled in good weather seasons. This paper describes a case study whereby inspection results are used to set the interval to the next inspection with the purpose of minmizing the maintenace costs.
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