Research On Residual Strength Of Jacket Platform With Fatigue Crack Damage

As the main working and living place of oil exploration and development, at present, there are more than 100 countries and regions in the world having conducted offshore oil and gas exploration and exploitation. As the platform served at the sea with serve environment for a long time, corrsion and crack are the common damage types of platform, which not only cause the decline of resistance ability of whole structure, but also threaten the use of oil resources, the protection of marine environment and the safety of the people. A succession of platforms’ capsizing cases at home and abroad caused huge economic losses、environment pollution and significant casualties. Therefore, it’s very important to analyze the effect of crack damage on the structural strength of offshore platform and evaluate the safety of platform reasonably. As the jacket platform is mainly used as oil production platform, fixed under the sea water and served for almost ten years, it will inevitably produce crack damage, with the difficulty of testing and fixing, which will directly affects the ultimate strength of platform. In this dissertation, as an example of the jacket platform, the effect of crack, especially through-thickness crack, on the structural ultimate strength of jacket platform are analyzed. Following research work have been studied specifically:1. This paper analyzes the research status of the influence of the crack on ultimatestrength of offshore structure; method for the research of ultimate strength isdiscussed.2. Propagation of fatigue crack based on the theory of fracture mechanic and nonlineareffects are discussed, multi-scale method is introduced in this paper, an numericalapproach containing some techniques to build and compute multi-scale model ofoffshore structure with crack damage are exposed.3. The key point of platform is obtained by ANSYS according to the structure type andload, meantime, get the crack size with time varying based on the fracture mechanic,and the applicability and feasibility of the ultimate strength analysis of structures areanalyzed by comparison, which creat the conditions for analyzing the nonlinearbehavior of large marine structures with crack damage.4. The jacket platform with time varying carck is bulit, the influence of crack size,uniform corrosion and weld on the fatigue life is considered under load. Thecontrolling effect factors that affect the fatigue life of platform are determined,meanwhile, influence of crack of different joints on the fatigue life is analyzed. 5. The jacket platform with time varying carck is bulit, get the changing rule of residualstrength of platform with the time-varying crack. Crack area which has obviousinfluence on the residual strength of whole structure is selected as analysis object,considering the effects of crack size, weld and uniform corrosion on the ultimatestrength of platform, meantime, the residual strength of platform with crack of jointsis analyzed.