Under normal circumstances, our commonly used pipeline flanges are used in pairs. Low-pressure pipelines can use wire flanges, and welding flanges can be used with pressures above four kilograms. Add a sealing gasket between the two flanges and tighten them with bolts. Flanges of different pressures have different thicknesses and use different bolts.
According to the connection method and flange connection type, flanges are divided into:
Flange connection form:
Flange connection:
It consists of a pair of flanges, a gasket and several bolts and nuts. Flange connection is a detachable connection.
Principle:
The gasket is placed between the sealing surfaces of the two flanges. After the nut is tightened, the specific pressure on the surface of the gasket reaches a certain value and then deforms, filling the uneven spots on the sealing surface to make the connection tight and leak-proof.
Performance:
It has good strength and sealing performance, simple structure, low cost, can be disassembled repeatedly, and is widely used.
Failure form:
The main manifestation is leakage, and the leakage amount is controlled within the allowable range of the process and environment.
According to the connected parts, it can be divided into a container flange and a pipe flange.
The integral flange refers to the inlet and outlet flange that connects pumps, valves, machines, and other mechanical equipment to pipelines. It is usually integrated with these pipeline equipment and serves as a part of the equipment.
Threaded flange is a non-welded flange that processes the inner hole of the flange into pipe threads and cooperates with threaded pipes to achieve connection. Compared with welding flanges, it has the characteristics of convenient installation and maintenance and can be used in some situations where welding is not allowed on-site. However, when the temperature is higher than 260°C and lower than -45°C, it is recommended not to use threaded flanges to avoid leakage.
Flat welding flange is also called a lap welding flange. The connection between the flat welding flange and the pipe is to insert the pipe into the inner hole of the flange to the appropriate position, and then lap weld it. Its advantage is that it is easier to center during welding assembly and it is cheap, so it has been widely used. Calculated based on internal pressure, the strength of the flat welding flange is about two-thirds of the corresponding butt-welding flange, and the fatigue life is about one-third of the butt-welding flange. Therefore, flat welding flanges are only suitable for pipeline systems with relatively low-pressure levels and where pressure fluctuations, vibrations, and oscillations are not serious.
Flat welding flange: A flange that is directly welded to equipment or pipes through fillet welds. Its structure is simple and processing is convenient.
When used on containers, they are divided into Type A flat welding flanges and Type B flat welding flanges.
Type A flat welding flange is directly welded to the container, and the weld size is small or there is no groove for welding, which cannot ensure that the flange and the container are stressed at the same time; Type B flat welding flange is attached with a thicker nipple. The welding quality of the flange and the nipple is reliable, ensuring that the flange and the container are stressed at the same time. Flat welding flanges are widely used for the connection of medium and low-pressure vessels and pipelines.
Butt welding flange, also known as high-neck flange, has greater rigidity and is suitable for situations with higher pressure and temperature.
There are three types of plate flat welding flanges, neck flat welding flanges and neck butt welding flanges used on pipes.
Plate flat welding flange: Since the flange is directly welded to the steel pipe, the flange plate is in poor stress state during operation and is prone to deformation. Suitable for low-voltage applications.
Neck flat welding flange: Due to the addition of a thick-walled short flange neck, the stiffness of the flange is increased and the flange deformation is greatly reduced. Suitable for medium and low voltage situations.
Butt welding flange is also called the high neck flange. It is different from other flanges in that there is a long and inclined high neck from the welding point of the flange and pipe to the flange plate. The wall thickness of this high neck is along the height direction. The gradual transition into the pipe wall thickness improves stress discontinuities and therefore increases flange strength.
Butt welding flanges are mainly used in situations with harsh working conditions, such as situations where the flange is subject to greater stress due to thermal expansion or other loads of the pipeline, or where the stress changes repeatedly; pipelines with large pressure and temperature fluctuations and high temperature and high pressure and pipes with sub-zero temperatures.
Butt welding: Butt resistance welding (referred to as butt welding) is a type of resistance welding method that uses resistance heat to weld two workpieces simultaneously along the entire end face. Butt welding is widely used due to its high productivity and ease of automation.
Flange connection is also the most commonly used connection form for valves in the HVAC industry.
According to the shape of the joint surface, it can be divided into the following types:
Smooth type: used for valves with low pressure. Processing is relatively convenient.
Concave-convex type: The working pressure is high and medium-hard washers can be used.
Tongue-and-groove type: Gaskets with larger plastic deformation can be used. They are widely used in corrosive media and have better sealing effects.
