Ultimate Bearing Capacity Of The Offshore Platform Structure With Impacts Of Corrosion

With the development of the industrialization and the decrease of resources on land,people turn their attention to the sea. At present, there are more than100countries andregions in the world having conducted offshore oil exploration and exploitation. Comparedwith the oil in land, The features of offshore oil development include harsh environment、expensive drilling equipment、more destructive when an accident occurs. As the mainworking and living place of oil exploration and development, the structural safetyof offshore platform determines the use of oil resources, the protection of marineenvironment and the safety of the people. A succession of platforms’ capsizing cases athome and abroad caused huge economic losses、environment pollution and significantcasualties. Therefore, it’s very important to analyze the effect of corrosion damage on thestructural strength of offshore platform and evaluate the safety of platform reasonably. Asthe jacket platform is mainly used as oil production platform, fixed under the sea water andserved for almost ten years, it will inevitably produce corrosion, with the difficulty oftesting and servicing, which will directly affects the ultimate strength of platform. In thisdissertation, as an example of the jacket platform, the effect of corrosion, especially pittingcorrosion, on the structural ultimate strength of jacket platform are analyzed. Followingresearch work have been studied specifically:1. This paper analyzes the research status of the influence of corrosion on ultimatestrength of offshore structure; method for the research of nonlinear effects isdiscussed.2. Finite element model of offshore platform is built by using large-scale FEA softwareANSYS according to the structure type and design size of platform, the loads of thewind, wave, current and ice should be computed based on the local region, the maincontrol load of the platform is determined.3. The applicability and feasibility of the ultimate strength analysis of structures basedon ANSYS/LS-DYNA quasi-static method are analyzed by comparison, and beamcoupling shell jacket platform model is built based on the multi-scale theory, whichcreate the conditions for analyzing the nonlinear behavior of large marine structureswith pitting corrosion damage.4. The platform components model with uniform corrosion and pitting corrosion are built, the influence of pitting depth, pitting radius and uniform corrosion with samevolume loss on the ultimate strength of components are considered under shear andaxial compression. The controlling factors that affect the ultimate strength ofcomponents are determined, meanwhile, the influence of the degree of pit corrosionintensity (DOP) on the ultimate strength of components is analyzed.5. The finite element model of jacket platform with pit corrosion was built and analyzedthe effect of different distributional range of pit corrosion on the ultimate strength ofplatform by ANSYS/LS-DYNA quasi-static method. Serious corrosion area areselected as analysis object, considering the effects of different pitting density on theultimate strength of platform and analyzing the effect of uniform corrosion underthe same volume loss by comparative method.