Introduction to the structure and applications of gaskets

These all have **standards; you can check them out**

The principle for selecting gaskets is that, in applications with modest requirements, selection can be based on experience, with replacement only if they no longer meet the needs. However, for applications with strict requirements, such as equipment involving explosive, highly toxic, and flammable gases as well as highly corrosive liquids, reaction tanks and pipeline systems, the appropriate choice must be made based on the operating pressure, operating temperature, the corrosiveness of the sealing medium, and the design of the sealing surfaces. Generally, at normal temperature and low pressure, non-metallic soft gasket materials are chosen ； At medium pressure and high temperatures, a combination of metal and non-metal gaskets or metal gaskets should be used ； When there are significant fluctuations in temperature and pressure, choose gaskets with good elasticity or self-compressing properties ； In low-temperature, corrosive medium, or vacuum conditions, gaskets with special properties should be considered. It should be noted here the impact of the flange condition on gasket selection. Effect of flange type. Different flange types require different gaskets. Smooth-faced flanges are generally used only for low pressures, with soft, thin gaskets ； Under high pressure, if the flange has sufficient strength, a smooth-faced flange can also be used, but a thick, soft gasket should be employed, or a wound gasket with internal reinforcing rings or reinforcing rings. In such cases, metal gaskets are also not suitable, as the required clamping force is too high, causing significant deformation of the bolts and making it difficult to achieve a tight seal between the flanges. If metal gaskets are to be used, the smooth surface should be reduced to decrease the contact area with the gasket. In this way, with the same bolt tension, the compressive stress on the reduced narrow smooth surface increases. Effect of flange surface roughness. The surface roughness of the flange has a significant impact on the sealing performance; especially when non-soft gaskets are used, high roughness of the sealing surface is one of the main causes of leakage. For example, the cut pattern on the turned flange surface is spiral-shaped. When metal shims are used, if the roughness value is high, the shims cannot block this spiral groove formed by the cut pattern, and under pressure, the fluid will leak out along this groove. Soft gaskets require much less precision in the finish of the flange surface, as they are prone to deformation and can fill in the machining marks, thereby preventing leaks. For soft gaskets, an overly smooth flange surface is actually disadvantageous, as it reduces the resistance to interfacial leakage. Therefore, different gaskets require different surface roughness levels for the flanges.

In fact, the choice is mainly based on the type of flange, the properties of the material, as well as the process pressure and temperature. You can look up a chemical process design manual; it contains detailed information on this topic.

Refer to HG20606--20614, HG20627--20635

You can refer to HG/T20592-2009 for steel pipe flanges, gaskets, and fasteners

There are many types of gaskets. When selecting a gasket, five factors should be considered: S for size, T for temperature, A for the type of equipment flange, M for the medium, and P for pressure. Regarding the structure and material of the gasket, relevant standards can be referred to. The choice of gasket depends on the medium, temperature, and pressure, which determine the appropriate material and design