| Due to offshore platform structure is complex, the structural integrity and safety of the platform are directly affected by the flow load and corrosion fatigue. SPAR platform, as a deepwater floating production system, its dynamic performance is high, and now is increasingly widely used in ocean engineering, particularly applicable to the extraction of oil and gas resources in deep water. Marine environment of the South China Sea is complex and changeable, so fatigue characteristics of offshore platform structure become high-cycle, nonlinear, variable and corrosion damages show changeable, irregular features. Dynamic performance of SPAR platform suitable for deep water of the South China Sea is studied, then stress response of the platform is analysed and the corrosion fatigue life is predicted, it has important practical significance for improving development ability of marine platform in the deep-water and oil and gas resources exploitation efficiency.Pitting corrosion is a major type of corrosive damage to offshore platforms. Based on the ASTM standard, pitting corrosion model is established, the effect of main dimensions of corrosion pits on the structural stress concentration is analysed, the development rule of corrosion pit size is summarized, the hot spot stress is magnified to consider the pitting corrosion on fatigue effects according to the effective stress concentration coefficient, and then calculation method of the corrosion fatigue life combined with the critical plane energy method which is suitable for offshore platform is determined. Based on the South China Sea marine environment, the environmental parameters of the South China Sea referring to DNV specification is determined in extreme working conditions, the model of Truss SPAR platform for the South China Sea conditions is set up, and the dynamic response of platform structure is analysed under extreme conditions. The exercise performance is assessed through the frequency domain dynamic response results and the time domain response results are obquired to assess its safety performance. The stress of fairlead in time history is calculated under working condition, combined with DNV positioning mooring specification and API specification, coupling point between main structure of platform and the mooring system- the fairlead is determinated, the service life of fairlead as key structure of SPAR platform combined with method of calculation of corrosion fatigue life is evaluated.The results show that the pitting corrosion is the maximum impact on the structural stress concentration, formula of effective stress concentration factor is determined by the measured data and the simulation analysis.The working and extreme sea condition of the south China sea waves flow parameters is determined, the truss SPAR platform model is set up. Frequency-domain dynamic results on the extreme sea condition show that the platform motion performance is good, and the time-domain dynamic results show that the platform limited displacement and force of mooring system both are in the allowable range, conforming to the safety performance. Based on calculated results of the stress concentration coefficient under different years, the hot spot stress is enlarged, the calculated corrosion fatigue life of the SPAR platform combined with the critical plane energy method is 224.0605 years, conform to partial designed life of floating production system of the ABS specification under the deep ocean. |
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