Detailed explanation of the difference between neck welding flanges and neck flat welding flanges

What is the difference between neck welding flange and neck flat welding flange?

1、 Different connection methods

The biggest difference between neck flat welding flanges and neck butt welding flanges is the connection method between the pipeline and the flange. Flat welding flanges with necks are usually connected by flange angles, while butt welding flanges with necks are the joints between flanges and pipelines.

Flat welding flanges with necks can only be connected to pipelines and cannot be directly connected to butt welded pipelines. Neck welded flanges can usually be directly connected to all butt welded fittings, including pipelines.

The stiffness of neck welding flanges is greater than that of neck flat welding flanges, and the welding strength is higher than that of flat welding flanges, making them less prone to leakage.

The neck flat welding flange and neck butt welding flange cannot be replaced at will. From a manufacturing perspective, flat welding flanges with necks have large internal warping, light weight, and low cost. In addition, neck welding flanges with a nominal diameter greater than 250mm also need to be tested, and their flanges do not require testing, 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 welding flanges are used for hazardous 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 used to connect flanges and pipelines. When welding flat welding flanges, only single-sided welding is required, without the need to weld pipes and flange connections. The welding installation of welded flanges requires double-sided welding of the flanges. Therefore, flat welding flanges are usually used for low and medium pressure pipelines, and welding flanges are used for connecting medium and high pressurepipelines. 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 relatively high.

2、 Different welding forms

Flat welds cannot undergo radiographic testing, while butt welds can. The butt weld at the neck is the circumferential weld between the flange and the pipeline. Flat welding is two fillet welds, and butt welding is a butt circumferential 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 points 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 the protruding platform without a flange is also a right angle welding. The weld between the neck butt flange and the connecting pipe belongs to Class B weld, while the weld between the neck flat flange and the connecting pipe belongs to Class C weld, and the non-destructive testing after welding is different.

3、 Different materials

The flange material with neck flat welding is processed with thick ordinary steel plate as required, while the flange material with neck butt welding is mainly processed with forged steel parts. Different nominal pressures.

The nominal pressure of the flange with neck flat welding is 0.6-4.0 MPa, and the nominal pressure of the flange with neck welding 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 neck welding flange and the pipeline joint belongs to Class C weld seam, and the non-destructive testing after welding is different.

Flat welding flanges with necks and welding flanges with butt joints cannot be replaced at will. From a manufacturing perspective, shrink fit flat welding flanges have large internal warping, light weight, and low cost. In addition, if the nominal diameter is greater than 250mm, the welded flange also needs to be inspected, and there is no need to inspect the flange, resulting in low cost.