The hemispherical head is a hemispherical shell.
Under uniform internal pressure, the film stress is half that of a cylinder of the same diameter. The spherical head has a small surface area per unit volume, stress is small under the same conditions of diameter, wall thickness and working pressure, and the stress of the two-way film is equal, and it is uniformly distributed along the warp. If connected to a cylinder with equal wall thickness, the stress near the edge is not significantly different from the film stress. But the depth is large, the diameter is small, and the overall punching is difficult. The use of split punching for large diameters has a large amount of tailor welding work.