In the flange sealing process, the flange preload force is a serious factor affecting the seal. The preload force must compress the gasket and achieve the initial sealing premise.
Flange bolt pre-tightening force is the pre-tightening force in the direction of the axis of the bolt generated between the bolt and the connected part under the tightening torque during the bolt tightening process. For a particular bolt, the magnitude of its preload force is related to the tightening torque of the bolt, the friction between the bolt and the nut, and the friction between the nut and the connected part.
The flange sealing preload is reported to the gasket through the flange pressing surface. Therefore, to achieve a delicate seal, the preload must be evenly impregnated into the gasket. Therefore, when the preload required for sealing is positive, it is beneficial to seal by reducing the bolt diameter and increasing the number of bolts. .
The pre-tightening of the flange can improve the reliability, anti-loosening ability and fatigue strength of the bolt connection, and enhance the tightness and rigidity of the connection. In fact, a large number of tests and experience have proved that: higher pretension force is beneficial to the reliability of the connection and the life of the connection, especially for the connection with sealing requirements.
The sealing surface of the large tongue-and-groove flange is composed of a tongue-and-groove surface and a groove surface. The gasket is placed in the groove. Applicable gaskets are: metal and non-metal flat gaskets, metal-clad gaskets, winding gaskets (basic type), etc.
Like the concave-convex flange, the large tongue-and-groove flange will not be squeezed out of the groove, the compacting area is the smallest (only 52 ~ 68% of the flat flange and the concave-convex flange), and the gasket is evenly stressed. Because the gasket is not in direct contact with the medium, the medium has the least corrosion effect and the penetration effect of the pressure mechanism. It can be used in high-pressure, flammable, explosive, toxic media and other strict sealing requirements. The sealing surface gasket has good neutrality during installation, and it is more difficult to process the sealing surface and replace the gasket.
The type and size of the large tongue and groove face flange with a nominal pressure PN of 4.0, 6.3, and 10.0 MPA face and welded steel pipe flange.
Large tongue-and-groove flanges are used for welding steel pipe flanges with a nominal pressure of PN4.0 ~ 10.0MPA.
The composition of the national standard large-scale insulating flange consists of installing a flange insulating gasket between two pieces of butt welding flat flanges and an insulating sleeve and an insulating bolt gasket on the fastening connecting bolts. The flange insulation gasket material of the national standard large-scale insulating flange is made of oil-resistant rubber asbestos sheet, neoprene sheet, fabric-based neoprene sheet and polytetrafluoroethylene. Insulation bolt sleeves and bolt insulation gaskets are made of high-strength phenolic laminated cloth sheets and pressed cloth pipes. Its characteristics are: good rigidity, stable insulation performance, special installation location and high cost.
The national standard large insulation flange is mainly used between gas transmission and distribution pipelines and gas pressure regulation, metering, storage and other equipment. Its main role is to insulate and isolate each section of the gas transmission and distribution pipelines, equipment and pipelines from each other, to protect them from Chemical corrosion will prolong the service life of pipelines and equipment. The product conforms to the SY / T0516-1997 “National Standard Design Technical Regulations for Large Insulation Flanges” standard.
The working principle of the national standard large insulating flange is to use the electrical insulation properties of the insulating gasket and high-strength insulating sleeve gasket in the national standard large insulating flange to perform electrical insulation on both sides of the national standard large insulating flange. According to the actual project, the insulation performance of the national standard large insulation flange is in accordance with the relevant requirements in the “National Standard Design Specification for Large Insulation Flange” (SY / T0516-1997) and the “Test Method for Cathodic Protection Parameters of Buried Steel Pipelines” 》 (SYJ23-86), the test results show that: the resistance value of the insulating gasket and the insulating sleeve of the fastening bolt between the insulating working surfaces can meet the specification requirements.
