Flat weld neck flanges and butt welding neck flanges cannot be used interchangeably. From a manufacturing point of view, the inner diameter of the necked flat welded flange is large, which means lightweight and low cost. In addition, butt welding neck flanges (WN referred to as welding neck) with a nominal diameter greater than 250 mm need to be tested. The SO with butt-welding neck flange does not need to be tested, so the cost is relatively low. Imported petroleum equipment widely uses necked horizontal welding, similar to the S0 standard of the American Standard, and necked welding flanges are used for high-risk media.
The distinction and difference between butt weld neck flanges and flat weld neck flanges:
1. Different welding seam methods: The welding seam of flat welding cannot be radiographically inspected, but the welding seam of butt welding can. The welding seam method of necked flat welded flange pipe and the flange is fillet weld, while the welding seam method of necked butt welded flange and pipe is girth weld; flat weld is two fillet girth welds, Buttweld is a butt girth weld. The difference between a flat-welded flange with a neck and a flat-welded flange without a neck is that a flat-welded flange with a neck has one more place in the pipeline welding position than a flat-welded flange without a neck. The flat welding method without a neck The flange is also a flat flange, and the boss without flange is also a flat fillet weld. The welded seam of the necked butt-welded flange and the receiving joint belongs to the class B seam, and the welded seam of the necked flat-welded flange and the receiving joint belongs to the class C seam, and the non-destructive testing after welding is different.
2. The nominal pressure is different: the nominal pressure of the flat weld neck flange is: 0.6—4.0MPa, while the nominal pressure of the butt weld neck flange is: 1–25MPa grade, obviously, the necked flat welded flange The adaptation pressure level is lower.
3. Different connection methods: the biggest difference in structure between flat welding neck flanges and butt welding neck flanges lies in the different connection methods of receiving and flanges, and necked flat welding flanges are generally receiving and flange corner joints. , And the neck butt welding flange is the flange and the receiving butt joint.
Neck flat welding flanges generally can only be connected to pipes, but not directly connected 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 pipes.
The rigidity of the necked butt welding flange is greater than that of the necked flat welding flange, and the butt welding has higher strength than the flat welding, and it is not easy to leak.
The flat welding neck flange and the butt welding neck flange cannot be replaced at will. From the viewpoint of production, the necked flat welding flange (SO is the abbreviation of SLIP ON) has a large internal diameter, which means a small weight and a low cost. Other nominal names Neck butt welding flanges (WN is the abbreviation of WELDING NECK) with a diameter greater than 250mm need to be tested, and SO flanges do not need to be tested, so the cost is relatively low.
Neck flat welding is used more on imported petroleum installations. Similar to the S0 of the American standard, neck butt welding flanges are used for highly damaging media.