The flat-head double-opening nozzle structure is widely used in equipment such as plate and shell heat exchangers in the petroleum, chemical and energy industries. There are structural discontinuities in the opening nozzle area of the flat head, resulting in complex stress distribution and local stress concentration in the nozzle area. The external load of the flat head taking over the pipe, such as the coupling of the pipe bending moment, axial force, and torque, will also make the stress distribution in the pipe connection area more complicated. Therefore, it is necessary to study the stress distribution law in the nozzle area of the flat head. GB150.1～150.4-2011 "Pressure Vessels" clearly stipulates the opening requirements and opening reinforcement conditions, and ASME BPVC SEC Ⅷ-2013 "Alternative Rules for Construction of Pressure Vessels" also points out the pressure shells that bear pressure loads. Reasonable design requirements near the opening on the body.

　　Analyze the influence of the axial external force acting on the end face of the nozzle on the strength calculation results of the pressure vessel connection part under internal pressure through an example, and discuss the influence of the direction and magnitude of the axial external force of the nozzle on different types of container shells.

　　The elastic stress of the opening structure of the container under the action of the bending moment of the nozzle is studied. The influence of the axial load and the bending moment of the pipe coupling with the internal pressure on the strength performance of the cylinder.

　　ANSYS finite element software was used to analyze the stress of the cylindrical double-opening structure. Based on the theory of precise cylindrical thin shells, the theoretical solutions of the cylindrical shells with radial nozzles under internal pressure and combined loads are solved, and the elastic stress analysis and design methods in these two cases are studied.

　　The influence of parameters such as the inner diameter of the nozzle, the angle between the cylinder and the centerline of the miter tube, the thickness of the nozzle, the fillet and chamfer of the miter tube, etc., on the discontinuous stress distribution of the miter tube is studied. At present, there are few domestic studies on the stress distribution of the double-opening nozzle with a flat head under the coupling of external load and internal pressure. For this reason, using the finite element analysis software ANSYS, the linear elastic analysis method and the ultimate load analysis method are used to analyze the stress of the flat head double-opening nozzle structure under the coupling of axial load and internal pressure.