Important position of pipe fitting cap

　　The opposite radial displacement occurs at the connecting part, which strengthens and counteracts most of the radial displacement, so that the circumferential compressive stress of the cylinder cap the circumferential tensile stress of the pipe fitting caps.

　　When the elliptical pipe fitting caps and the cylinder are connected, the bending radius of the elliptical pipe fitting caps is continuous and does not produce stress, so it can be used in the container of higher pressure, while the disc. The connection of shaped pipe fittings cap is discontinuous and the productivity stress is generally applied in low pressure vessel, especially for stamping and butterfly pipe fitting caps.

　　The structural discontinuity zone of pressure vessel is usually the high stress zone of pressure vessel. Generally speaking, the structural discontinuity zone of pressure vessel can be divided into two types: the general structural discontinuity zone and the local structural discontinuity zone.

　　Overall structural discontinuity refers to the stress or strain sources that affect a considerable part of the structure, such as the joint area between pipe fitting caps and shell, flange and shell, nozzle area, joint area of different diameters or thicknesses or materials, etc. Local structural discontinuity refers to the stress that affects a relatively small area of the structure. Or strain sources, such as small fillet radius, small connectors, partially penetrated welds or holes, etc. Many structures, such as pressure vessel nozzles with openings, have both overall structural discontinuity and local structural discontinuity. Because the geometric structure of discontinuous zone is usually complex, it is difficult to solve it accurately by analytic method, and the finite element method is usually used to calculate it.