PSI - Issue 57

Arne Fjeldstad et al. / Procedia Structural Integrity 57 (2024) 692–700 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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they present is of great importance. Inspection activities have the potential to impact the operation of the FPSO. Therefore, it is important to optimize inspection resources and optimize the process. In this context, the adoption of campaign-based inspection strategies proves invaluable. Rather than planning individual inspections on each detail, a campaign-based approach is employed, offering a practical and cost-effective solution. Careful planning and scheduling of inspection activities are important to minimize disruptions to routine operations. The objective is to achieve a balance that ensures thorough inspections while minimizing the impact on the FPSO's operation. Entry into compartments such as ballast tanks, cargo tanks, voids, and cofferdams are planned at regular intervals. For cargo tanks, specific procedures must be followed before inspections can occur. Thorough washing of the tanks and complete removal of any hydrocarbon gases are necessary to create a safe and conducive environment for inspection activities. In the case of ballast tanks, the FPSO needs to be re-ballasted before the inspection can take place. These examples highlight the balance that must be maintained between regular operation and inspections with optimal intervals. While ensuring structural integrity remains a top priority, continuous operation is vital for the efficiency of the FPSO. GVI plays a crucial role in campaign-based inspections as it serves as the initial assessment of the overall condition of structural details. GVI involves a visual examination to identify visible signs of damage, degradation, or irregularities. Non-Destructive Testing (NDT) inspections is based on details with low calculated fatigue lives and high consequences of failure. These critical components, typically identified through probabilistic fracture mechanics analyses, pose a higher risk of developing fatigue cracks and demand greater attention. NDT techniques such as ultrasonic testing, magnetic particle inspection, and eddy current testing are employed to comprehensively evaluate their integrity and identify potential cracks. Close Visual Inspection (CVI) serves as a valuable tool within the inspection framework, both as a supplement and a replacement for NDT techniques. CVI is particularly advantageous for inspecting specific types of well-defined details, such as bracket terminations, where cracks are more likely to be detected, even during CVI. Furthermore, CVI is employed when multiple details require inspection, allowing for a targeted and streamlined approach. By strategically utilizing CVI, the reliance on time consuming NDT techniques can be reduced, optimizing inspection resources and improving overall efficiency. By implementing these inspection strategies, including GVI, NDT inspections, and CVI, FPSO operators can efficiently allocate inspection resources and effectively address potential fatigue cracks in ship compartments. This approach ensures the preservation of structural integrity while minimizing disruptions to operations, contributing to both safety and the overall economic efficiency of the FPSO. References Bjørheim, L. (2006). Fatigue Assessment of Long Through Thickness Fatigue Cracks in Ship Hulls, PhD Thesis, Dept. Marine Tech. NTNU, Trondheim, ISBN:82-471-7754-4. Bowness, D. and Lee, M. M. K. (2002). Fracture Mechanics Assessment of Fatigue Cracks in Offshore Tubular Structures. Offshore Technology Report 2000/077. HSE. ISBN 0-7176-2328-9. DNV-RP-C203 (2019) Fatigue design of offshore steel structures DNV-RP-C210 (2019) Probabilistic methods for planning of inspection fir fatigue cracks in offshore structures. Itagaki, H, Akita, Y, and Nitta, A. (1983). Application of Subjective Reliability Analysis to the Evaluation of Inspection Procedures on Ship Structures, Role of Design, Inspection, and Redundancy in Marine Structural Reliability, Proc. Int. Symp., ISBN: 0-309-03488-4, National Academy Press. Landet, E., Lotsberg, I. and Sigurdsson, G. Risk-Based Inspection of an FPSO. OTC 12146.Offshore Technology Conference, Houston. 2000. Landet, E., Oma, N., Ersdal, G., Sigurdsson, G. and Sørensen, T. 2011. Assessment of ageing structures – Case studies. OMAE2011-49959. Proceedings of OMAE2011, 30 th International Conference on Ocean, Offshore and Arctic Engineering. 2011. Lotsberg, I., Sigurdsson, G., and Wold P. T. (1999). Probabilistic inspection planning of the Åsgard A FPSO hull structure with respect to fatigue. OMAE99/S&R-6040. Proceedings of OMAE99, 18 th International Conference on Offshore Mechanics and Arctic Engineering. 1999. Lotsberg, I. and Sigurdsson, G. 2014. A New Recommended Practice for Inspection Planning of Fatigue Cracks in Offshore Structures based on Probabilistic Methods. OMAE2014-23188. Proceedings of OMAE2014, 33 rd International Conference on Ocean, Offshore and Arctic Engineering. 2014. Lotsberg, I., Sigurdsson, G., Fjeldstad, A. and Moan, T. (2016). Probabilistic methods for planning of inspection for fatigue cracks in offshore structures. Journal of Marine Structures 46, 167-192. Madsen, H. O. (1985). Model Updating in First-Order Reliability Theory with Application to Fatigue Crack Growth, Proc. of 2nd Int. Workshop on Stochastic Methods in Structural Mechanics, University of Paris, France.