The head is one of the components of the pressure vessel. It is the end cap on the pressure vessel and a main pressure-bearing part of the pressure vessel. The head is an indispensable and important part of the pressure vessel equipment in the nuclear, petrochemical, food and pharmaceutical industries. The components are very versatile and can be used in various container equipment, such as storage tanks, heat exchangers, towers, reactors, boilers, separation equipment, etc.

　　There are many classification methods for heads. According to the geometry of the heads, the heads can be divided into spherical heads, oval heads, dish heads, spherical crown heads, cone shell heads and flat heads. There are six types, of which spherical heads, elliptical heads, dish-shaped heads and spherical cap heads are collectively called convex heads; according to the welding method of the heads, they can be divided into butt-welded heads and bearing heads. There are two types of plug-welded heads.

　　The materials of the head include carbon steel, stainless steel, alloy steel, aluminum, titanium, copper, nickel and nickel alloys. Its working principle is to seal the pressure vessel of the equipment. It can be used for both the upper and lower bottom of the tank-shaped pressure vessel and the two ends of the pipeline. Generally, it cannot be disassembled after the head is welded. The main fittings for the head include pipelines, pressure vessels, flanges, elbows, tees, crosses, etc. The quality of the head directly affects the safety of the pressure vessel. According to the relevant regulations of "Pressure Vessel Head", the minimum forming thickness of the head should be controlled. Therefore, in the manufacture of the head, it is necessary to determine the minimum forming thickness of the head and subsequent inspection issues.

　　As a pressure vessel head, its minimum thickness should meet the requirements of the "Pressure Vessel Head" standards and drawings, that is, the minimum forming thickness of the head should be greater than the nominal thickness of the head minus the negative deviation C1 of the steel plate thickness. In general, the reduction rate of the forming thickness of the head is between 12% and 16%. Therefore, if the steel heads for pressure vessels are pressed with steel plates whose thickness is marked by the design drawings, it will not meet the requirements of the standard. Only the steel plate with a thickness above the thickness of the drawing can be used to press the steel head of the pressure vessel, that is, the thickness of the blank should be greater than the thickness of the drawing. For example, the head formed by using 8mm blank steel plate can meet the requirement of "when the design drawing indicates the minimum thickness of the head after forming, the minimum thickness measured shall not be less than the minimum thickness marked on the drawing". In addition, the "Pressure Vessel Head" also stipulates the minimum forming thickness of the head. At the current stage, there are currently two marking methods when designing head drawings. Most head designers adopt the method of marking the nominal thickness of the head in the design drawings, while a small number of designers adopt double marking methods. , That is, the nominal thickness and minimum thickness of the head are marked at the same time. The nominal thickness refers to the thickness of the steel standard specification after the design thickness plus the negative deviation of the steel thickness.