Study On Structural Health Condition Management During The Whole Life Cycle Of Deep-water Semi-submersible Platform

The structures of platforms may have some corrosion damnifications due to the effect of marine environment, which would decrease the structural safeties during their whole life cycle. In this paper, a deep-water semi-submersible platform was selected as the target platform. The residual yield strength and buckling strength of the target platform with different corrosion damnifications have been calculated, and the influences due to the corrosion damnifications for different structures of the platform have also been discussed. It is concluded that the influences of the structures exposed to full immersion zone and splash zone of the platform are much larger than others, and these structures should be effectively protected by using appropriate corrosion control measures.Being the familiar and vital structures in platforms, the fatigue lives of K-tubular joints should been calculated by using appropriate method. Models for several different K-tubular joints of the target platform have been established with finer meshing by using ANSYS, and the hotspot stresses of tubular joints have been calculated based on the methods prescribed by ABS rules. The fatigue life assessments have been done by using spectral fatigue analyses method, and the method was performed on practical engineering structures successfully. The position of crack initiation was selected based on the results of fatigue assessments and the crack models with different sizes for K-tubular joint have been established with solid element by using ANSYS. The stress intensity factors in crack tips have been calculated for fatigue damaged K-tubular joint under practical sea environment, and the residual strength of fatigue damaged tubular joint has also been discussed. Based on the law and mechanism of fatigue crack growth for practical structure, and take the fracture failure under low stresses into consideration, a calculated method of limit crack size for K-tubular joints of the target platform has been proposed, which could provide technique support for maintenance and detection of the target platform during the whole life cycle.The braces and tubular joints of the target platform are very complicated, and lose their resistance easily under the effect of corrosion and fatigue. It will result in plenty of troubles for the structural health condition management during the whole life cycle of the target platform. To decrease the cost for maintenance and detection and improve the economic benefits, the structural safety of the target platform has been studied under the case that some structures failed, and a management proposal of structural health condition for target platform during the whole life cycle has been formed, and the validity of the management proposal has also been verified.