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The generation and characteristics of edge stress: The shells of pressure vessels used in actual production processes are basically composed of simple shell shapes such as spherical shells, cylindrical shells, and conical shells. The generatrices of these shells are not single, simple curves; rather, they are combinations of multiple curves. In other words, the shell can be regarded as being formed by rotating a specific combined curve around an axis, which results in discontinuities at the joints where the generatrices meet, and thus leads to discontinuities in stress at those joints. Furthermore, changes in the thickness, load, material, temperature difference, and so on of the housing along the axial direction can also cause discontinuous stresses at the joints. The discontinuous stresses generated at the connection edges are collectively referred to as edge stresses. Shell combinations that are different result in varying edge stresses at the connection edges. In some cases, the edge stress is quite significant, with stress values that can reach very high levels. However, they have one distinct characteristic: they decay rapidly and have a limited range of influence. The stress exists only in a localized area at the edge; it drops to zero quickly in areas slightly away from the edge. This property of edge stress is commonly referred to as locality. The analysis shows that for ordinary steel, the edge stress decreases by 95.7% at a distance of 2.5sqrt(Rδ) from the edge, where δ is the thickness of the shell and R is the radius of the shell. Furthermore, edge stress arises from the mismatched elastic deformation of the shell on both sides of the edge, as well as the elastic constraints between their deformations. However, in the case of shells made from plastic materials, when the material in the local area at the joint edge undergoes plastic deformation, the original elastic constraints are relieved, causing the previously different deformations to become coordinated immediately; the deformation does not continue to develop, and the edge stress is automatically limited. This property is known as the self-limiting nature of edge stress. Measures to reduce edge stress: 1. Reduce the stiffness difference between the two connectors. Inconsistent deformation of the two connectors can cause edge stress. Shell stiffness is related to factors such as the material’s elastic modulus, radius of curvature, and thickness. Trying to reduce the stiffness difference between the two connectors is one of the effective measures to lower edge stress. Two cylinders with the same diameter and material are connected together; when their wall thicknesses differ, discontinuities arise under internal pressure, resulting in edge stresses. If the thick cylindrical sections of different thicknesses are thinned within a certain range, the edge stress can be reduced. When the difference between the two thicknesses is small, the single-sided thinning structure shown in Figure (a) can be used ； When the difference between the two thicknesses is large, a double-sided thinning structure is advisable. 2. Try to use arc transitions; sudden changes in geometric dimensions and shapes are one of the main causes of stress concentration. To reduce stress concentration, arc transitions or specially shaped, optimized curves are preferably used at structural discontinuities. For example, on the inner surface of a flat-ended head, the maximum stress occurs near the internal corner A; by using transition arcs with a radius of not less than 0.5δp and (Dc/6), the edge stresses resulting from structural discontinuities can be reduced. 3. Local reinforcement: In areas of the shell where local loads are applied, such as at the junction between the shell and the lifting lugs, or at the connection between a horizontal container and a saddle support, a gasket is placed between the shell and the attached components to provide appropriate reinforcement, thereby effectively reducing local stresses. 4. Select the appropriate opening orientation: Based on the effect of loads on the cylinder, choose the suitable location, direction, and shape for the openings. For example, the long axis of elliptical or oblong holes should be parallel to the direction of the maximum stress at that point; holes should be placed in areas where the stress level is relatively low, as this can also help reduce local stresses.