Study On The Effect Of Out-of-Roundness On The Cylinders Shell Under External Pressure In Stability Numerical Calculation

Cylindrical shell under external pressure is widely used in the industry. It is important to keep the vessel safe and reliable operation, the stability is the important condition for the vessel run normally. The material and geometric nonlinearity often make it difficult to research the buckling problem by theoretical or analytical solution. With the development of numerical methods, many scholars using the technology of FEA researching the buckling of cylinders subjected to external pressure, but there isn’t a exactly method to be present. In this paper, research the effect of roundness deviation on the buckling of cylinders shell under external pressure.The first concern is the relationship between the numerical simulation results, and experimental value or standard value. The critical pressures of external pressure cylinder were simulated by ANSYS’s GMNIA (Geometrical and Material Nonlinear Analysis with Imperfections included). The comparison was performed between the critical pressure values from simulation and calculated by GB150, ASME VIII-2and EN13445. The result show that the simulated critical pressure is lower than both of the test result in literature and the corrected result which calculated by Mises formula considering nonlinear material property. In the elastic instability stage, some allowed external pressure simulated by ANASYS using the design factor in the section5of ASME Ⅷ-2are slightly higher than that from the ASME Ⅷ-2formula method, also some slightly lower than that from GB150. However, in non-elastic instability stage, the simulated allowed pressures are lower than that from ASME VIII-2formula method and EN13445, and are higher than that from GB150.Then study on the problem of material and geometric model in numerical calculation. By the research of four material models and four geometric models, the result shows that the material model of MPC is a security model. And the Consistent defect mode method also is a conservative method.Last analyze the maximum roundness deviation of a cylinder that the buckling pressure will not be less than80%of the perfect cylinder. The results show that:when the L/Do is small, with the L/Do value increases, the cylinder can withstand the roundness deviation value decreases. In the case of a larger L/Do value, with L/Do value increases, the sensitivity of the cylinder on the roundness deviation is reduced.The deficiencies and flaws is inevitably. In the follow study, there is a further research and analysis the problem of material models and FEA model. And in order to universality of the conclusion, it is necessary need to research the bucking of cylinder under external pressure combine the FEA and the probability method.