Common factors affecting flange seals
Leakage of the flange seal is mainly caused by leakage between the sealing faces. The possibility of leakage by the capillary action of the gasket is small. After the gasket is pressed by an external force, the elastic deformation and plastic deformation of the gasket itself fill the gap of the uneven surface on the sealing surface, so that the resistance of the medium passing through the sealing surface is greater than the pressure difference between the two sides of the sealing surface, that is, seal. However, when it is affected by external conditions, the seal is damaged, resulting in leakage. The factors affecting the seal are mainly as follows:
(1) The influence of operating conditions. Operating conditions are pressure, temperature, and physicochemical properties of the medium. In petrochemical plants, there are many low-pressure flanges, and the influence of simple pressure or medium factors on flange leakage is not the main one. The problem only becomes serious when combined with temperature. When the temperature changes repeatedly, the seal is more likely to fail.
(2) The influence of the gasket coefficient and the compression ratio in the design parameters. China's current selection of the two parameters is through the look-up table "steel pressure vessel", but the gasket coefficient and compression ratio, even the same material, the two coefficients are also with the width of the gasket, pre-tightening pressure, medium properties, flange The sealing surface width and roughness are related to each other. Therefore, there are no authoritative specifications to choose from.
(3) The influence of bolt preload. Increasing the pre-tightening force of the bolt can increase the sealing performance of the gasket. However, if the bolt and the elf are too large, the gasket will lose its elasticity and even crush the gasket or the foundation. It cannot guarantee that it has sufficient elasticity under working conditions. .
(4) The influence of gasket performance. The gasket deformation includes elastic deformation and plastic deformation. Gasket material is the main factor affecting the performance of the gasket, so the quality of the gasket will affect the sealing of the flange.
(5) The influence of flange stiffness. Insufficient flange stiffness can cause excessive warpage and is often one of the causes of seal failure.
(6) The influence of the sealing surface. The shape and roughness of the flange sealing surface should match the gasket. The flatness of the sealing surface and the perpendicularity of the sealing surface to the axis of the flange are prerequisites for ensuring uniform compression of the gasket. Therefore, the influence of reasoning or eccentric force caused by thermal expansion of the pipeline must be considered in design and installation. Otherwise, it will easily cause the flange to be tightly sealed and cause leakage.