1. Elliptical head

　　The hoop stress and axial stress of the elliptical head change at each point on the shell. The hoop stress and the axial stress at the apex are equal, while the stress at the equator. When the elliptical head is subjected to uniform internal pressure, the axial stress is always a tensile stress (positive value), and gradually decreases from the maximum at the apex to the equator to the minimum; when the hoop stress is present, pressure will begin to appear in the transition zone of the head Stress, if the ratio of long and short axis continues to increase, the compressive stress value at the edge of the head transition zone will increase rapidly, that is, the shallower the head, the higher the compressive stress value at the edge of the head, so the ratio of the long and short axis of the head is limited to 2.6 It is more reasonable within. In addition to meeting the strength requirements, the thickness of the head should also be used for large-diameter and thin-walled elliptical heads. The compressive stress in the transition zone of the head should also be used to produce elastic instability under internal pressure. Meet the rigidity requirements.

　　2. Torispherical head

　　The torispherical head consists of three parts: a spherical part, a straight side part and a transition zone. The transition zone connects the spherical part and the straight side section, so there is a sudden change in the curvature radius of the warp at both ends of the transition zone, which will produce edge stress. The size of the edge stress of the dish-shaped head is related to the ratio of the radius of the transition zone to the radius of the spherical surface. The smaller the ratio, the more severe the sudden change of the curvature border and the greater the edge stress. When the ratio reaches the limit, that is, the radius of the transition zone is 0, the dish-shaped seal The head evolves into a spherical cap and a straight cylinder, and the edge stress reaches the maximum at this time. Therefore, the transition area of the dish-shaped head is to reduce the edge stress, and the straight side part is to avoid the edge stress from acting on the welding seam connecting the head and the cylinder.

　　3. Spherical head

　　The radius of curvature of the spherical crown-shaped head at the junction of the spherical surface and the cylinder undergoes abrupt changes. At the same time, because the two shells have no common tangent, there is a lateral thrust, so considerable discontinuous stress is generated. Therefore, this kind of head can only be used in occasions where the pressure is not high, and the fillet weld connecting the head and the cylinder must adopt a full penetration structure.

　　When designing the spherical crown-shaped head, it should be noted that the thickness of the cylinder connected to the head should not be less than the thickness of the head, otherwise a strengthening section transition connection should be provided between the head and the cylinder.

　　4. Conical head

　　When does the taper head take the edge folding, the Angle limit and so on refer to the relevant section of GB150.Here is an internal pressure - free flanged tapered head.

　　Under the internal pressure of the main part of the cone, the maximum film stress occurs at the big end.At the connection of cone and cylinder, due to geometric discontinuity and abrupt change of radius of curvature, there will be greater lateral thrust, leading to greater edge stress and prone to bending, so it needs to be strengthened.For the big end, the axial bending stress is the main control factor, and it belongs to the secondary stress, so the stress intensity is controlled.For the small end, the stress condition at the connection between the small end and the cylinder is mainly the average circumferential tensile stress and the average radial compressive stress, belonging to the local thin film stress, so the stress intensity can be controlled.