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Selection of gaskets: The principle for selecting gaskets is that, in situations where high requirements are not necessary, a choice can be made based on experience, with replacement only if they become unsuitable. 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, corrosivity of the sealing medium, and the type of sealing surface. Generally, at normal temperature and low pressure, non-metallic soft gasket materials are chosen ； At medium pressure and high temperatures, a composite metal-non-metal gasket or a metal gasket 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 or external 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, a high roughness value 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 gaskets are used, if the roughness value is high, the gasket 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.