The difference between flat welding and butt welding of flanges

First of all, we need to know what is a butt welding flange and a flat welding flange.

The main differences between the two flanges are as follows:

1. Different forms of welds: The welds of flat welding cannot be detected by radiographs, but the welds of butt welding can be. The welding seam between the pipe and the flange of the neck flat welding flange is a fillet weld, while the welding seam between the neck butt welding flange and the pipe is a girth weld; the flat welding is two fillet girth welds, A butt weld is a butt girth weld. The difference between the flat welding flange with neck and the flat welding flange without neck is that the flat welding flange with neck has one more welding position in the pipeline than the flat welding flange without neck, and the flat welding method without neck The flange is also a flat flange, and the boss without a flange is also a flat fillet weld. The welding seam connecting the neck butt welding flange and the connecting pipe belongs to the B type seam, and the welding seam connecting the neck flat welding flange and the connecting pipe belongs to the C type seam, and the non-destructive testing after welding is different.

2. The material is different: the material of the flat welding neck flange is machined from ordinary steel plates with a thickness that meets the requirements, while the material of the neck butt welding flange is mostly machined from forged steel.

3. The nominal pressure is different: the nominal pressure of the neck flat welding flange is: 0.6-4.0MPa, and the nominal pressure of the neck butt welding flange is: 1-25MPa. Obviously, the neck flat welding flange is suitable The pressure level is lower.

4. Different connection methods: The biggest difference in structure between the neck flat welding flange and the neck butt welding flange is the difference in the connection between the connecting pipe and the flange. The neck flat welding flange is generally the connection between the connecting pipe and the flange. The neck butt welding flange is the butt joint between the flange and the pipe. Flat welding flanges can generally only be connected to pipelines, but not directly to butt-welding pipe fittings; butt-welding flanges can generally be directly connected to all butt-welding pipe fittings (including elbows, tees, reducers, etc.), of course Also includes plumbing. The rigidity of the neck butt welding flange is higher than that of the neck flat welding flange, and the butt welding is stronger than the flat welding, and it is not easy to leak. Slip-on neck flanges and butt-welding neck flanges cannot be replaced casually. From the perspective of manufacturing, the flat-welding neck flanges have a large inner diameter, which means small weight and low cost. In addition, butt-welding neck flanges with a nominal diameter greater than 250mm The flange needs to be tested, so the flange does not need to be tested, so the cost is relatively low. Neck flat welding is widely used in imported oil installations, similar to American standard S0, neck butt welding flanges are used for highly hazardous media.

The flat welding of the flange is mainly used for the flat welding flange, and the butt welding is mainly used for the butt welding flange. The difference between the flat welding flange and the butt welding flange is whether there is a neck; the flat welding flange has only one flange ring surface , when welding with the nozzle, it is a 90° welding angle, which is called flat welding; the butt welding flange has an extra flange neck compared to the flat welding flange, and the diameter of the flange neck and the nozzle is the same, and the nozzle and the butt welding When the flanges are butt-jointed, a 45° bevel is opened at the interface (there are also other angles, depending on the process), and the nozzle and the flange neck form an angle of 180°, and are directly welded at the bevel, which is called butt welding.
In short, flat welds – 90°, butt welds – 180°.

Flat welded steel flange: suitable for steel pipe connections with nominal pressure not exceeding 2.5MPa. The sealing surface of flat welded flange can be made into three types: smooth type, concave-convex type and tongue and groove type. The application amount of smooth flat welded flange Larger. It is mostly used in the case of moderate media conditions, such as low-pressure non-purified compressed air and low-pressure circulating water. Its advantage is that the price is relatively cheap

Butt welded steel flange: used for butt welding between flange and pipe. It has reasonable structure, high strength and rigidity, can withstand high temperature and high pressure, repeated bending and temperature fluctuation, and has reliable sealing performance. The nominal pressure is 0.25 ~ 2.5MPa The butt welding flange adopts a concave-convex sealing surface.

For flat welding flanges, the inner diameter of the flange is equivalent to the outer diameter of the pipe. The pipe is found to be welded to the flange, and both the inner and outer sides can be welded according to the situation. The butt welding flange refers to the high and medium pressure flange with a neck, which is higher than the back of the flange, and is used for welding.