First, the type of flange
Structure type: Pipe flanges are divided into the following basic types according to the connection with pipes: flat welding, butt welding, socket welding, loose sleeves, threaded flanges and integral flanges.
Sealing surface type: The flange sealing surface has a full plane, a convex surface, a concave surface, a ring groove surface, a groove surface, and the like.
Several common codes for flanges (representation): Different standards have slightly different names and codes for the sealing faces and types of flanges.
Second, flat welding flange
It is used on pipelines for public works. It is suitable for pipelines with low pressure level, pressure, temperature fluctuation and vibration, and its strength is lower than that of the equivalent butt weld flange.
Butt welding flange: the commonly used high-strength flange is a commonly used flange. Since the flange and the pipe are welded with a long and inclined neck, the strength of the flange is increased and it can be used for high or low temperature. A place with a high level of strictness.
Loose flange: For the precious material, consider its economical, that is, the pipe joint and the flange sleeve are made of different materials.
In addition, there are thread and socket connections, which are different ways of connecting the flange and the pipe, and the connection form of the flange face is also different according to the sealing requirements.
Third, the choice of sealing surface type
1. Full-face sealing surface: It is often used in applications where operating conditions are low. When P≤0.1Mpa, it is often used for cast iron and cast steel flanges.
2, convex table sealing surface: is a widely used one, commonly used in PN2.0Mpa, PN5.0Mpa, PN1.6Mpa pressure level.
3, concave and convex sealing surface: commonly used in the PN4.0Mpa grade, but it is not convenient to replace the gasket.
4, ring groove surface sealing surface: often used in conjunction with the butt welding connection type, mainly used in high temperature, high pressure, high conditions, PN10.0Mpa, PN25.0Mpa, PN32.0Mpa and other pressure levels.
Fourth, the gasket
The bolt is pressed by the load of the bolt to make it elastically deform, and the microscopic geometric gap between the sealing surface of the flange and the gasket is filled to reduce the leakage of the medium. The performance of the gasket and the suitability of the selection have a great influence on the sealing effect. The commonly used gaskets can be divided into three categories, namely non-metal gaskets, semi-metal gaskets and metal gaskets.
1. Non-metallic gasket: It is made by adding different additives to asbestos.
Scope of application: T≤2600C PN≤PN2.0Mpa For use in water, air, alkali, oil and other media.
2, polytetrafluoroethylene (PTFE) package gasket
Scope of application: T=-1800C-2000C, PN≤PN 4.0Mpa
Commonly used low temperature or when the requirements are relatively clean.
3, semi-metal gasket: There are three types of winding gaskets, metal coated gaskets and flexible graphite spiral gaskets.
The wound gasket is the most ideal among the semi-metal gaskets, and it is also the most common gasket. It is characterized by good elasticity of the compression surface, high strength, and good sealing performance under high temperature and low temperature vibration.
4. Metal gaskets are often placed on high pressure grade flanges to withstand relatively high seal pressures.
Commonly used metal gaskets are flat cushions, octagonal cushions and elliptical cushions. Metal gaskets are commonly used with concave and convex surfaces, bossing surfaces, and grooved flanges.
Five, bolts, nuts
When selecting fastener materials for flange connection, factors such as operating pressure, operating temperature, type of media, and type of gasket should be considered.
Alloy steel bolts are made of high-quality steel, that is, the material grade should be added with the letter A, such as the commonly used 35GMOA, 25GM0VA.
Hex head bolts: commonly used with flat welding flanges and non-metallic gaskets for less demanding conditions, the common material for hex head bolts is Q235B.
Studs: Commonly used in the case of welded flanges. Under the most demanding conditions, the nut material is usually determined according to the bolt material to be matched with it (usually grade 8.8 and above).
In order to make a good seal, in addition to the above-mentioned suitable matching flanges and gaskets, it is also necessary to pay attention to the cleanliness of the flange sealing surface and the verticality of the flange welding. During the installation process, tighten the bolts and install the gaskets in strict accordance with the operating procedures to avoid biasing the gaskets.
At the same time, we must pay attention to daily maintenance and maintenance during the operation process to ensure the lubrication of bolts and nut fasteners.
In short, there is a good sealing pair to ensure safe and smooth operation of the pressure regulating station (pressure regulating device) or gas equipment.
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