Common sealing structures for high-pressure vessels – Discussion

Thread Content

The quality of the sealing in a high-pressure sealing structure is directly related to the safety of using the container; it constitutes the core part of such containers. Whether the design of this sealing structure is scientific and reasonable not only affects the normal operation of the container but also poses significant risks to its reliability and safety. 　 　When designing high-pressure sealing structures, it is necessary to take into account various influencing factors, including the environment in which the container will be used. Factors such as extreme pressures, high temperatures, and even significant temperature fluctuations must all be considered to ensure the safe use of the container as well as its sealing performance. Furthermore, in addition to having the necessary sealing reliability, the structure must be as simple as possible to facilitate easy daily installation, maintenance, and disassembly, as well as to simplify repairs. 　　Although the machining precision and surface finish of the sealing structure are not very high, the material of the sealing element must be resistant to medium corrosion and possess the strength to withstand multiple repeated uses. To meet the increasingly high demands in production and daily life, there is an urgent need for ceiling sealing structures capable of withstanding higher pressures in order to fulfill various production requirements. 　　1 Analysis of Several Traditional Sealing Structures for High-Pressure Vessel Heads and Their Defects 　　1.1 Flat Gasket Sealing 　　Metal flat gasket sealing is a commonly used sealing structure in the market; it belongs to the category of forced-sealing mechanisms. The sealing principle of this structure is relatively simple – pressure sealing is achieved through preload and operating pressure, with both of these pressures coming from the compressive force exerted by the main bolts on the large flanges at the ends of the cylinder. The main factor affecting the strength of the structural pre-tensioning force is the yield strength of the gasket material; in addition, the width of the gasket is also an important influencing factor. The greatest advantage of metal flat gasket seals is their simple structure, which reduces the construction and assembly time as well as the complexity involved. They require few sophisticated processing equipment, and thanks to years of development, the processing techniques related to them are now quite mature. Due to the limited range of applications for metal flat gaskets, which can only be used in environments where the temperature is below 200°C, the pressure is less than 32 MPa, and the inner diameter of the container is no more than 800 mm, their applicable conditions are quite limited. When the pressure increases and higher pressure levels are required, it is necessary to make adjustments to the bolts and increase the size of the structure; this raises the complexity of the sealing mechanism and also increases the weight of the structure as well as the entire container. The complexity of such structures also poses many difficulties in terms of installation and disassembly. 　　1.2 Biconical Seal The biconical seal is an improved semi-self-sealing structure that retains the main bolt design; its sealing surface consists of a combination of two semi-circular or triangular grooves. Its sealing principle is that, under the high temperature and pressure conditions inside the container, the biconical ring expands due to heat, undergoes elastic deformation, which increases the specific pressure on the sealing surface. Since the sealing gasket materials in this structure are soft steel and stainless steel, and the shape of the sealing surface is conical, the high-pressure environment causes the double-cone ring to expand radially outward, thereby **increasing the sealing pressure on the sealing surface and achieving the sealing effect required for production. Twin-cone seals have strong resistance to environmental conditions, allowing them to be used in a wide range of applications, especially in environments with excessive pressure, high temperatures, and large diameters. Furthermore, this sealing structure is relatively simple, making it easy to manufacture and assemble; it also does not require high precision in manufacturing. Structural adjustments can be made in a short time as needed when the environment changes. The disadvantage of this structure is that it requires high bolt pre-tension and axial force; a large sealing pressure must be applied to achieve sealing, and at the same time the structural components are large and complex. 　　1.3 B-ring sealing The B-ring seal has a high tolerance for high-temperature environments; even in harsh conditions, it maintains stable reliability and safety in terms of sealing performance. The B-ring seal is a self-sealing mechanism; it requires low stiffness in the connecting structure, and its sealing performance is positively correlated with environmental pressure and temperature – the higher the pressure and the larger the diameter, the better the sealing effect of the structure. Since the initial specific pressure for B-ring sealing is achieved through radial interference between the wave peaks of the B-ring and the sealing grooves on the cylinder and cover to provide pre-sealing, high precision is required in the manufacturing of these sealing rings; such stringent requirements make production difficult. Moreover, the difficulty in removing them poses challenges for subsequent maintenance, and it is easy to damage the contact surfaces. 　　2 D-bolt connected C-ring high-pressure sealing device. The top cover of the D-bolt connected C-ring high-pressure sealing device is placed within the flange at the end of the cylinder; by reducing the diameter and thickness of this top cover, it still maintains excellent performance in terms of the compactness of the overall structure as well as its structural quality. The D-bolts connect the top cover of the C-ring high-pressure sealing device to the inner surface of the end flange, with 1/4 of the length of the bolt holes for these D-bolts located on the end flange during processing. The D-bolts are installed in an \"eccentric\" manner throughout the annular gap between the top cover and the end flange. A certain gap is reserved between the top cover and the end flanges to provide space for the installation of the C-ring and the gasket. 　　In the high-pressure sealing device with a C-ring connected by D-bolts, under the action of the internal pressure of the medium, the self-sealing property of the C-ring increases the tightening force applied by the set screw. It is important to note that before carrying out the structural installation, all D-bolts on the top cover should be loosened; the top cover assembly is then placed inside the flange cavity, and axial as well as circumferential positioning is performed. When the removal of the cover and the end flange is relatively simple, it is sufficient to rotate the D-bolts approximately 90° in the reverse direction to remove the cover assembly from within the end flange, thereby enabling quick installation and removal of the container cover without the need for any additional hydraulic wrenches. Moreover, the D-bolt has a simple structure, requires low precision and complexity in component fabrication, and is widely used; it finds extensive application in high-pressure and ultra-high-pressure container sealing systems across various industries such as chemicals and energy. 　　3 A new high-pressure sealing structure based on O-rings The triple-seal O-ring is composed of two sealing grooves together with the cylinder wall, with the rubber ring arranged circumferentially along the flat cover. The shear ring of the flat cover is composed of evenly spaced sector-shaped ring segments and circular ring segments with parallel sides, arranged alternately; each sector-shaped ring segment and circular ring segment has screw holes along its radial direction. The radial seal **increases the compression rate of the pre-sealed condition through the dimension chain, thereby enhancing the reliability of the radial triple seal** ； The radial seal on the bracket, together with the seals in the axial direction, ensures complete sealing of the sealing structure.