In pressure vessels, compared with other forms of heads, semi-circular heads have the best stress distribution, require the smallest thickness under the same diameter and pressure, and save the most materials. Therefore, they are often used in high-pressure vessels. At the same time, among all forms of connections between the head and the cylinder, the thickness difference between the semi-circular head and the cylinder is the largest. The connection structure between them not only affects the manufacturing of the equipment, but also is one of the important factors for the safe operation of the container. In GBl50-1998, the circumferential weld seam between the cylinder and the semi-circular head is also defined as a Class A welded joint.
The habit of processing semi-circular head materials has a long history and a wide range. In order to effectively control the entire process of head manufacturing, promote the scale and specialization of head manufacturing, standardize the head market, and ensure the safety of special equipment such as pressure vessels, it is necessary for the Special Equipment Safety Supervision Bureau to deploy safety supervision and inspection and pressure vessels in various regions. The semi-circular head manufacturing unit strictly controls the input and output of incoming materials for processing, clarifies their respective legal responsibilities, eliminates counterfeit and illegal manufacturing, and continuously purifies and regulates the market for special equipment heads such as pressure vessels.