Risk based Fatigue Inspection Planning – State of the Art

The present paper presents the methodology and the practical calculations for risk based inspection planning of fatigue cracks in welded offshore steel structures. Due to the uncertainty in the variables involved in the problem the planning has to be carried out by stochastic modeling and risk based assessments. Scatter in potential crack growth has to be analyzed by applied probabilistic facture mechanics and the uncertainty in the performance of the actual inspection technique has to be determined. With given risk acceptance criteria the practical outcome of the analyses is recommended inspection techniques and associated planned inspection time intervals. The classical theory is briefly outlined and the latest recommendations from a Joint Industry Project recently completed in Norway are included. A practical case study for life extension of an oil loading system in the North Sea is presented.