Using finite element elastic-plastic buckling analysis and considering the maximum shape deviation of the elliptical head and by applying a local thickness thinning defects in the transition zone, the variation law of buckling load Pcr with limit load PL of the standard elliptical head under internal pressure was systematically discussed for different materials and thickness diame- ter ratioδe /Di.The results show that when the thickness-diameter ratio is less than a critical value, the buckling load is lower than the limit load, and the buckling failure occurs for the elliptical head analysis model, whereas the thickness-diameter ratio is greater than a critical value, the buckling load is higher than the limit load, and the strength failure may occur for the elliptical head anal- ysis model. There are some differences in the critical values of thickness-diameter ratio for analysis models of different materials. For high strength steel material 13MnNiMoR, the thickness-diameter ratio stipulated in GB 150—2011 code to prevent the failure of elastic buckling of standard elliptical heads under internal pressure may lead to insufficient safety margin. The results of this study provide guidance for the design criteria of standard thin wall elliptical heads under internal pressure.

　　The elliptical head is one of the most widely used heads in medium and low pressure vessels due to the smooth and continuous change of the warp curvature of the ellipsoid part, the relatively uniform stress distribution, and the easy stamping and forming. The research on internal pressure elastic buckling of elliptical heads began in the 1950s. Galletly conducted a linear elastic analysis of the buckling failure of a large-diameter vulcanized coker during the hydrostatic pressure test, and found that the transition section of the elliptical head was in a compressed state; subsequently, Bushnell performed the elastic buckling load of the elliptical head under internal pressure. In order to prevent the circumferential stress in the corner area of the elliptical head from causing instability, Shield gave the elastic buckling load of the elliptical head. With reference to the research results of some documents, my country’s GB 150-2011 stipulates that in order to prevent elastic instability under internal pressure, the effective thickness of the standard elliptical head should not be less than 0.15% of the internal diameter of the head (non-standard elliptical head is 0.3%). The elastic buckling pressure expression for convex heads provided by WRC Bulletin compares the elastic buckling load and strength failure load of elliptical heads with different diameter-thickness ratios for several groups of commonly used materials. It is considered that GB 150-2011 is for elliptical heads The regulation of internal pressure instability is not comprehensive enough and deserves further study. With the development of finite element technology and numerical simulation software, a large number of scholars have performed numerical simulations on the elastoplastic buckling behavior of convex heads. Bushnell used the BOSOR5 finite element program to analyze the buckling load of the dish head under internal pressure, and compared the test results. Galletly conducted an elastoplastic buckling test study on the dish-shaped head under internal pressure. The deformation curve of the transition section was obtained through the probe, and the buckling behavior was successfully obtained. Through internal pressure test, topography scanning and numerical simulation, Zhou Yi obtained the deformation law of the transition section between the elliptical head and the barrel section. The numerical simulation results are relatively consistent with the experimental results. Tao Weiming used the finite element software ABAQUS to analyze the local plastic buckling problem in the transition zone of the dish-shaped head, and proposed that the real geometry and defects of the structure should be measured as much as possible to ensure that the simulation results are close to the test. Zhang Tong conducted a nonlinear buckling analysis of the internal pressure dish-shaped head based on ABAQUS, and the calculated critical buckling load was close to the previous test results, capturing the complete buckling and post-buckling path and shape.

　　Using finite element elasto-plastic analysis, a more systematic discussion of standard elliptical heads under different materials and different thickness-to-diameter ratiosδe /Di. Analyze the change law of structural internal pressure buckling load Pcr and ultimate load PL, and compare and analyze with the regulations in the current standard GB 150-2011, and get the following conclusions:

　　(1) Using the arc length method in ANSYS software to perform nonlinear buckling analysis of a certain dish head, and analyze the local transition zone of the dish head

　　Introducing a single defect of 15% thickness reduction, the calculated bifurcation buckling load of 0.597 MPa is basically consistent with the previous test value of 0.609 MPa, which shows the reliability of the finite element internal pressure buckling analysis solution in this paper.

　　(2) When the aspect ratio is less than a certain critical value, the buckling load is lower than the limit load, and the analysis model undergoes buckling failure; when the aspect ratio is greater than a certain critical value, the buckling load is higher than the limit load, and the analysis model undergoes strength yield failure. The critical value of the thickness-to-diameter ratio of the standard elliptical head analysis model of different materials is different, but it is basically in the range of 1.4‰ to 1.9‰.

　　GB 150-2011 stipulates that the minimum thickness-to-diameter ratio to prevent elastic buckling failure of the internal pressure standard elliptical head is 1.5‰, which is too strict for the high-strength steel 13MnNiMoR material.