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Typically, a hemispherical head is half a spherical shell or half a spherical shell with cylindrical straight edges. The connection between the hemispherical shell and the straight edges or cylinder is a tangential connection; therefore, there is no lateral thrust, and the edge stresses are low enough to be ignored. A flangeless spherical head consists of portions of the spherical shell that are directly welded to the cylindrical shell or flange, with interlaced non-tangent connections. There is a circumferential tensile force on the cylindrical shell at the connection point in the tangent direction of the spherical shell. To this end, GB150 adopts design principles based on stress classification, determining the wall thickness of flangeless spherical heads by ensuring that the maximum combined radial tensile stress at the joint edge is ≤ 3t. For hemispherical heads, the outer surface of the cylinder at the joint edge experiences the maximum circumferential combined tensile stress, with a value of only 1.031pR/δ; whereas in hemispherical heads, the maximum circumferential tensile stress occurs on both the inner and outer surfaces at the joint edge, but this value is lower, at just 0.75pR/δ. It can be seen that when a hemispherical head with the same thickness as the cylinder body is used, the influence of boundary effects is minimal; in such cases, design can be carried out based solely on membrane stresses, without needing to consider the effect of edge stresses.