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In offshore steel structures engineers often face the problem of assessing the criticality of existing hot spots to predict the remaining lifetime and thus to develop sound reliability-based inspection programs. One problem with such an approach is that the past fatigue conditions cannot be appropriately modeled, and the degree to which damage has accumulated in hot spot areas cannot be consistently modeled. This paper shows a practical methodology for predicting the remaining fatigue life of hot spots by using a probabilistic fracture mechanics approach and shows how in general the results can be used in reliability-based inspection programs. Introduction At present, the best practice for modeling remaining fatigue life and identifying hot spots in existing offshore steel structures is the traditional S-N approach (Miner's rule). The uncertainties in the S-N approach for existing structures are significant, and it is often impossible to take into account the stress cycles to which the structure has been subjected in the past, especially in cases where the structure has been strengthened or modified. This results often in very low fatigue life, sometimes even lower than the actual age of the structure. The S-N approach has thus only limited use for identifying measures and for establishing risk- and reliability-based inspection plans for such hot spots in existing structures. The present paper shows how a probabilistic fracture mechanics approach can be used to analyze the existing hot spots in an offshore steel structure and how reliability-based inspection planning can be established based on these results. The general approach is to postulate cracks of specific length and depth that match the threshold of known inspection techniques, to have cracks located in specific directions at the hot spot locations, and then to predict the crack growth and failure probability of the postulated cracks.
Abstract In offshore steel structures engineers are often facing the problem to assess the criticality of existing hot spots, to predict the remaining life time and thus to develop sound reliability based inspection programs. One problem in such an approach is that the past fatigue conditions cannot be appropriately modelled and it cannot be modelled consistently to which degree damage has already accumulated in the hot spot areas. In this paper a practical methodology is shown how to predict the remaining fatigue live of hot spots by using a probabilistic fracture mechanics approach and how in general the results can be used in for reliability based inspection programs. INTRODUCTION The present best practice for modelling remaining fatigue lives and identifying hot spots in existing offshore steel structures is the traditional S-N approach (Miners rule). The uncertainties in the S-N approach for existing structures are significant and it is often impossible to take the stress cycles to which the structure has been subjected in the past into account, especially in cases where the structure has been strengthened or modified. This results often in very low fatigue lives, sometimes even lower than the actual age of the structure. The S-N approach has thus only limited use for identifying measures and for establishing risk and reliability based inspection plans for such hot spots in existing structures. In the present paper it is shown how a probabilistic fracture mechanics approach can be used to analyze the existing hot spots in an offshore steel structure and how reliability based inspection planning can be established based on these results. The general approach is to postulate cracks of specific length and depth matching threshold of known inspection techniques and to have cracks located in specific directions at the hot spot locations and then predict the crack growth and failure probability of the postulated cracks.
- Well Completion > Hydraulic Fracturing (1.00)
- Reservoir Description and Dynamics (1.00)
Abstract In this paper a practical application of a probabilistic fracture mechanics approach in an existing and damaged offshore structure is presented. Taking basis in the global wave load modelling and FEA models of the structure the stresses and fatigue cycles at existing cracks are modelled in a probabilistic manner. The failure probability of the cracks in the present and future states are calculated and probabilistic predictions of the crack growth are made. Finally, an outlook on possible usage of the results is given and advantages of a probabilistic analysis are discussed.
- Europe > Denmark (0.47)
- North America > United States (0.29)
- Europe > Switzerland (0.28)
- Well Completion > Hydraulic Fracturing (1.00)
- Reservoir Description and Dynamics > Reserves Evaluation > Probabilistic methods (0.49)
- Well Drilling > Drilling Operations > Drilling operation management (0.34)
- Information Technology > Artificial Intelligence (0.49)
- Information Technology > Data Science (0.34)