What is the difference between neck welded flange and neck flat welded flange?
1、 Different connection methods
The biggest difference between neck flat welding flange and neck butt welding flange is the connection method between the pipeline and flange. Flat welded flanges with a neck are usually connected at a flange angle, while butt welded flanges with a neck are the butt joint between the flange and the pipeline.
Flat welding flanges with necks can only be connected to pipelines and cannot be directly connected to butt welded pipelines. A neck welded flange can usually be directly connected to all butt welded fittings, including pipes.
The stiffness of the neck welded flange is greater than that of the neck flat welded flange, and the welding strength is higher than that of the flat welded flange, making it less prone to leakage.
Necked flat welding flanges and necked butt welding flanges cannot be replaced arbitrarily. From a manufacturing perspective, flat welded flanges with necks have large internal warping, light weight, and low cost. In addition, neck welded flanges with a nominal diameter greater than 250mm also need to be tested, and their flanges do not need to be tested, so the cost is relatively low.
Flat welding flanges with necks are widely used in imported petroleum equipment, similar to the American standard S0. Neck welded flanges are used for harmful media. Neck welding flange refers to the diameter and wall thickness of the connecting end. Same as the pipeline to be welded, just like welding two pipelines.
Flat welding and butt welding refer to the welding methods for connecting flanges and pipes. When welding flat welding flanges, only one side welding is required, and there is no need to weld pipes and flange connections. The welding installation of welding flanges requires double-sided welding of the flanges. Therefore, flat welding flanges are usually used for low-pressure and medium pressure pipelines, and welding flanges are used for medium and high pressure pipeline connections. Welding flanges are usually at least PN2.5MPa, and butt welding is used to reduce stress concentration. Therefore, due to the increase in technology, the installation cost, labor cost, and auxiliary material cost of welding flanges are higher.
2、 Different welding forms
Flat welds cannot undergo radiographic testing, while butt welds can. The butt weld of the neck is the circumferential weld between the flange and the pipeline. Flat welding is two fillet welds, while butt welding is a butt ring weld. The difference between a flat welding flange with a neck and a flat welding flange without a neck is that a flat welding flange with a neck has more welding areas in the pipeline than a flat welding flange without a neck. A flat welding flange without a neck is also a flat welding flange, and a raised flange without a flange is also a right angle welding. The weld between the neck docking flange and the connecting pipe belongs to Class B weld, while the weld between the neck flat welding flange and the connecting pipe belongs to Class C weld, and the non-destructive testing after welding is different.
3、 Different materials
The material of the neck flat welding flange is processed with thick ordinary steel plates as required, while the material of the neck butt welding flange is mainly processed with forged steel parts. Different nominal pressures.
The nominal pressure of the neck flat welding flange is 0.6-4.0 MPa, and the nominal pressure of the neck welding flange is 1-25 MPa; The weld seam between the neck welding flange and the pipeline belongs to Class B weld seam, while the weld seam between the flat neck flange and the pipeline joint belongs to Class C weld seam, and the non-destructive testing after welding is different.
Flat welding flanges with neck and welding flanges with butt joints cannot be replaced arbitrarily. From a manufacturing perspective, the shrink fit flat welding flange has large internal warping, light weight, and low cost. In addition, if the nominal diameter is greater than 250mm, the welding flange also needs to be tested, and there is no need to test the flange, which is low-cost.