Flat Welding Flange
Flat welding flange refers to a type of flange that is connected to a container or pipeline using a fillet weld. It belongs to the category of arbitrary flanges. In the design, it is checked whether the flange is integral or loose, depending on the level of integrity of the flange ring and the straight section connection of the cylinder. The flanged ring is available in two types: necked and neckless.
Compared with the welding neck flange, the flat welding flange has a simpler structure and lower material cost, but its rigidity and sealing performance are inferior. Flat welding flanges are widely used in connecting medium and low pressure containers and pipelines.
Principles and Characteristics
The issue of the flat welding flange has always been a topic of concern regarding the cost of production or the economic benefits of companies and enterprises. Therefore, the sealing principle of flat welding flange is constantly being improved and perfected.
However, the main design flaw of the flat welding flange is that it cannot guarantee zero leakage. This is due to its design deficiency: the connection is dynamic and periodic loads such as thermal expansion and fluctuations will cause movement between the flange faces, affecting the function of the flange and ultimately compromising its integrity, resulting in leaks.
No product can be completely free from defects, but companies try to minimize the deficiencies of their products. Therefore, when producing flat welded flanges, the company strives to maximally improve product performance to maximize its effectiveness.
The characteristics of the flat welding flange are that it not only saves space and reduces weight, but more importantly, it ensures that the joint does not leak and has good sealing performance.
The reason why the size of the compact flange is reduced is because the diameter of the sealing element is reduced, which will reduce the cross-sectional area of the sealing surface.
Secondly, the flange gasket was replaced with a sealing ring to ensure the sealing surfaces matched. As a result, only a small amount of pressure is required to tighten the sealing surfaces.
As the required pressure decreases, the size and number of bolts can also be reduced correspondingly, resulting in a new product that is small in size and light in weight (reducing the weight of traditional flanges by 70% to 80%).
Therefore, flat welding flange is a relatively high-quality flange product that reduces quality and space and has played an important role in industrial applications.
The sealing principle of flat welding flange is that the two sealing surfaces of the screws compress the flange joint and form a seal, but this also leads to the destruction of the seal. To maintain the seal, a large force on the screw must be maintained, which means that the screws must be enlarged.
And larger bolts require larger nuts, which means that larger bolts are needed to create conditions for tightening the nuts. However, the larger the bolt diameter, the more the applicable flange will bend, and the only solution is to increase the wall thickness of the flange portion. The entire device will require enormous size and weight, which becomes a particular problem in offshore environments because weight is always the main concern.
Furthermore, fundamentally, the flat welding flange is an ineffective seal, requiring 50% of the bolt load to compress the gasket, leaving only 50% of the load to maintain pressure.
Welded Neck Flange
Welded neck flange is a type of pipe fitting that refers to a flange with a neck and a circular pipe transition, which is welded to the pipe for connection.
Welded neck flanges are not easily deformed and provide good sealing, making them widely used in various applications. They have corresponding stiffness and elasticity requirements as well as a reasonable reduction in thickness for the welding transition.
The distance between the weld and the joint face is large, which protects the joint face from being deformed by the welding temperature. They have a relatively complex conical structure and are suitable for high-temperature, high-pressure and low-temperature pipelines or pipelines that experience significant pressure or temperature fluctuations.
They are typically used to connect pipelines and valves with PN greater than 2.5 MPa and also to transport expensive, flammable and explosive media.
Socket Weld Flange
Socket welding flange refers to a type of flange in which the end of a pipe is inserted into a step inside the flange and then welded to the inside and outside of the pipe end. There are two types, one with a neck and one without.
Neck socket welding flange has good rigidity, small welding deformation and better sealing performance, and can be used in occasions where the pressure is between 1.0 ~ 10.0 MPa. Type B flange used in containers also belongs to socket weld flange and is used in occasions where high sealing requirements are required.
When designing, the socket weld flange can be checked according to the integral flange method.
Sliding flange
Sliding flange refers to a type of flange that slides over the end of a container or pipeline. Flanges are components used to connect shafts, mainly to connect pipes; There are also flanges used in equipment input and output connections to connect two pieces of equipment.
Sliding flanges belong to the loose flange category. The protruding edge can be made by flanging, direct turning or welding a separate ring.
The advantage of slip-on flanges is that they do not generate additional torque on the container or piping when the flange deforms, making them easy to manufacture and allowing them to be made from different materials than the container or piping, which can help save money. costs. metals.
The disadvantage is that the flange thickness is relatively large. Sliding flanges are suitable for situations where the container or pipeline is lined with fragile materials and the pressure is not high.
Threaded Flange
A threaded flange refers to a type of flange connected to a pipeline using threads. During the design process, it can be treated as a loose flange.
The advantage of this type of flange is that it does not require welding and the additional torque produced by deformation of the flange on the cylinder or pipe is minimal.
However, the disadvantage is that threaded flanges are thicker, which makes them more expensive. Threaded flanges are suitable for connecting high pressure pipelines.
Implementation Principle
Threaded flanges are a type of non-welded flange where the inner hole of the flange is machined into a pipe thread and connected to a threaded pipe to obtain a connection.
Compared with welding flanges such as slip-on flanges or butt-welded flanges, threaded flanges have the advantage of being easy to install and maintain. They can be used on pipelines where welding is not permitted. Alloy steel flanges have sufficient strength, but are not easy to weld or have poor welding performance, so threaded flanges can be used.
However, it is not recommended to use threaded flanges in conditions where the piping temperature changes rapidly or the temperature is above 260°C or below -45°C to prevent leakage.
Integral Flange
“Integral flange” is a kind of flange connection method and is a kind of neck welded steel pipe flange. The material used for integral flanges includes carbon steel, stainless steel, and alloy steel, among others. In several national standards, “IF” is used to indicate integral flanges. They are commonly used in high pressure piping and are typically manufactured through casting processes.
In terms of flange types, “IF” is used to represent integral flanges. The sealing surface of integral flanges is usually raised face (RF), but if used in environments with high fire, explosion or hazard risks, other types of sealing surfaces such as tongue and groove (MFM) or tongue and groove (MFM) TG) can be chosen instead of RF.
How can we distinguish welded neck flanges and integral flanges?
Both weld neck flanges and integral flanges use welding as a joining method and have a long neck. How can we distinguish welded neck flanges and integral flanges from their appearance and usage?
In terms of appearance, the end of an integral flange is thicker than that of a welded neck flange. Except for PN1.6MPa and DN450 or higher, the inner diameter of an integral flange is equal to its nominal diameter. The neck of an integral flange is higher and the wall thickness is relatively thicker, which can be clearly seen by referring to the standard neck welded flanges.
In terms of usage, integral flange is a type of flange that is connected to equipment such as valves, where the flange and valve are an integral whole, not connected by welding. Integral flanges are commonly used in equipment manufacturing and are rarely used in piping projects.
On the other hand, neck welded flanges are used in conjunction with equipment such as valves and pumps, and are welded directly to the pipeline. The end interface size of neck welded flanges is consistent with the outer diameter and wall thickness of the corresponding pipeline, making it suitable for direct welding connection.
