Torispherical Head

The butterfly head, also known as a folded-edge spherical head, is a widely used sealing configuration in pressure vessels. It consists of three main components: the spherical surface, the folded edge section, and the straight edge section. Compared to elliptical heads, it offers lower manufacturing complexity while meeting the pressure requirements of most medium-and low-pressure vessels, making it extensively applied in storage tanks, heat exchangers, and other pressurized equipment. China's current GB 25198 standard "Pressure Vessel Heads" specifies detailed requirements for the geometry, dimensional parameters, tolerance specifications, and technical conditions of butterfly heads. The standard defines the nominal diameter range as DN150 to DN6000, with applicable nominal thicknesses ranging from 3 mm to 100 mm. It further stipulates that the spherical radius must not exceed one times the nominal diameter, the folded-edge radius must be at least 10% of the nominal diameter, and the thickness must be no less than three times the nominal thickness—measures designed to ensure proper stress distribution under pressure. Additionally, the standard provides detailed specifications for internal dimensional tolerances, straight-edge height deviations, and thickness requirements, offering a unified framework for the design, manufacturing, and inspection of butterfly heads.