The Function of Sealing Gasket and How to Discern and Choose?
In the process of routine inspection, sealing gaskets are indispensable to boilers, pressure vessels, pressure pipes and other confined pressure devices. However, due to the lack of professional knowledge in the selection and application of sealing gaskets in most enterprises, some misunderstandings will inevitably arise if they are selected only by experience. As a result, the phenomena of running, running, dropping and leaking are common, causing a lot of waste to the unit, and even serious accidents due to the failure of sealing gaskets. This kind of situation is mainly caused by problems in the selection and assembly of sealing gaskets. In view of the above situation, it is necessary to make a more specific introduction to the selection of sealing gaskets.
I. The Function, Mechanism and Influencing Factors of Sealing Gaskets
The function of sealing gasket is to prevent the leakage of sealed medium, and the leakage can be divided into two forms: interface leakage and permeation leakage. The leakage of the interface is usually caused by the relaxation of the pressure between the sealing surfaces, aging, deformation, corrosion, wear or burn of the sealing surfaces, and mechanical vibration under working conditions. The leakage is related to the material types, manufacturing methods, properties of sealed media, working pressure and temperature of sealing gaskets.
In theory, even with gaskets, it is impossible to achieve full contact between sealing surfaces without any micro-channels or clearances. Although these channels are extremely narrow, they are still large enough relative to the molecular volume of the fluid medium. Therefore, it is impossible for the fluid to be completely blocked at the edge of the sealing surface. There will always be some fluids entering the sealing joint. There are complex hydrodynamic and thermodynamic processes between the contacts. It is generally believed that when the fluid enters the extremely fine and irregular gap between the sealing surfaces, it will produce resistance loss in the process of its flow to consume its energy. At the same time, it will produce a static boundary layer on the wall of these slots, so that the small channels become narrower or even completely blocked, so that the fluid entering the sealing surface can not continue to flow, so as to achieve sealing.
The main factors affecting the sealing are the following: the surface condition of the sealing surface; the contact width of the sealing surface; the nature of the fluid; the temperature of the fluid; the material of the sealing gasket; the pre-tightening force exerted on the sealing surface; and the influence of other external conditions (mainly the vibration of the system, the deformation of the connecting parts, the offset of the installation position, etc.). If the seal is reliable, these factors must be carefully considered, and the quality and selection of sealing gaskets are also crucial.
2. Selection of Sealing Gaskets
The factors to be considered in the selection of sealing gaskets are as follows:
- The nature of the fluid, i.e. the physical and chemical properties of the fluid medium in contact, will react with the gasket.
- The pressure of the fluid, i.e. the pressure state of the fluid medium, is a positive or negative pressure, the maximum working pressure, and whether there is pressure fluctuation and other factors.
- The temperature of the fluid, that is, the temperature condition of the fluid medium, and whether there is any temperature change during the operation, etc. 4. Flange type, i.e. flange shape, size, sealing surface condition, etc.
Under the above circumstances, we can refer to the relevant technical performance information of sealing gaskets, and select the suitable sealing gaskets for the working conditions of the sealing parts.
3. Assembly of Sealing Gaskets
The assembly of sealing gaskets is a key factor in practical application. Generally, the requirements for assembly are as follows.
- The surface of sealing gasket and flange sealing surface should be clean and clean.
- On the basis of accurately grasping the size of flange sealing surface, special tools are used to cut the sealing gasket material. Striking the flange edge is strictly prohibited to obtain the sealing gasket.
- The dimension of sealing gasket is slightly smaller than that of flange sealing surface and slightly larger than that of flange sealing surface. The difference is usually twice the thickness of sealing gasket.
- Before the pre-tightening of the gasket, the torque measuring wrench should be used to control the bolt tightening force, so as to avoid too large or too small the pre-tightening force and lead to the seal failure when the pre-tightening specific pressure of the gasket is known.
- When sealing gasket is preloaded, in order to make the gasket bear uniform force, diagonal preloading should be adopted, which can not reach the pre-tightening value at one time, and the pre-tightening value can be reached at 2-3 times in general circulation.
- When changing sealing gaskets, the properties of media, especially flammable and explosive media, should be considered. Safety tools should be used.
In order to make the seal reliable and durable, considering the safety, efficiency and waste of the unit, the selection and matching of sealing gaskets is an aspect that needs to be carefully considered when enterprises install, repair and transform.
Source: China Sealing Gaskets Manufacturer – Yaang Pipe Industry (www.steeljrv.com)
(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)
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