Investigation On Residual Strength Evaluation Method Of Pressured Equipment With Two Kinds Of Defects Based On FEM

In the 21^st century, on the one hand, as demand for saving resources is increasingly becoming urgent globally, the fitness-for-service （FFS） assessment on pressurized structures has attracted wide concern. On the other hand, the development of larger scale structures and working under extreme conditions also require in-service components to be assessed by FFS assessment. At present, our country also positively develops the FFS standards, but they still lag behind the advanced FFS standards. The assessment process has shortcomings of systematization and convenience.In GB/T19624-2004, it recorded assessment methods for plane flaws in detail, but rarely mentioned assessment methods for geometric imperfections and non-planar flaws.So in this thesis, it mainly researched the fitness-for-service assessment methods for misalignment defects on spherical tank and corrosion defects on pipelines. It also introduced the finite element safety evaluation method.As for misalignment, since there is no specific evaluation provision about the spherical tank with misalignment defect in GB/T 19624-2004 code, a three-level assessment method based on the Fitness-for-Service （FFS） Standard API579 was proposed to evaluate a large spherical tank with a misalignment defect that exceeded the tolerance. The work put emphasis on how to execute the finite element analysis of the Level 3 assessment procedure. A nonsymmetrical 3D model was established in accord with the practical situation, and the safety assessment was successfully executed to the high stress zone based on the FFS standard. The research results provide an available evaluation method for those in-service vessels with the related misalignment defects.As for corrosion defects, in this thesis, it used finite element method to simulate corroded pipelines, and compared the simulation results with experiment data to ensure the reliability of finite element model. It has also found that the prediction results of using solidl85 was more accurate than using solid 186, the time for simulation was also relatively shorter. Also, the thesis has compared 4 different kinds of remaining strength calculation methods for corroded pipelines and summarized the application scope of these evaluation methods.In addition, this thesis has also developed fitness-for-service assessment software which could assess the misalignment defects and corrosion defects. The software contains four modules, one- and two- level assessment for misalignment defected spherical tank and failure pressure prediction and maximum safety working pressure calculation for corroded pipeline.