What are the Main Differences Between Butt Welding Flanges and Flat Welding Flanges?

Butt-welding flanges and flat-welding flanges are two common types of flanges, and their main differences are reflected in the structural design, usage scenarios, installation methods and performance.

Flat welding flanges in general can only be connected with pipelines, but not directly connected with butt-welded pipe fittings; butt-welding flanges in general can be directly connected with all butt-welded pipe fittings (including elbows, tees, reducers, etc.), including pipelines of course. The stiffness of butt-welding flanges with necks is larger than that of flat-welding flanges with necks, and butt-welding is stronger than flat-welding and less prone to leakage.

1. The weld form is different: the weld of flat welding can't be ray detected, while the weld of butt welding can be. Flat welding flange with neck pipe and flange weld weld form of fillet weld, while the neck butt welding flange and pipe weld weld form of ring weld; flat welding is a two angle ring weld, butt welding is a butt ring weld. Flat welding flange with neck and not with the neck of the flat welding flange is the difference between the necked flat welding flange is not necked flat welding flange than in the pipeline welding parts to be more than one out of the neck, not with the neck of the flat welding flange is also a flat flange, there is no flange of the same flange is the same as a flat fillet weld seam. Butt-welding flange with neck and the receiver connected to the weld is a class B seam, flat welded flange with neck and the receiver connected to the weld is a class C seam, post-weld nondestructive testing is not the same.

2. Different materials: the material of necked flat weld flange is machined from ordinary steel plate with thickness in accordance with the requirements, while the material of necked butt weld flange is mostly machined from forged steel parts.

3. Different nominal pressure: the nominal pressure of necked plain welding flanges is 0.6---4.0MPa, while the nominal pressure of necked butt-welding flanges is 1--25MPa, obviously, the adapted pressure level of necked plain welding flanges is lower.

4. Different connection methods: The big difference between necked flat welding flange and necked butt welding flange in structure is the different connection methods between receiver and flange, necked flat welding flange is generally connected with the receiver and flange angle, while necked butt welding flange is connected with the receiver.

5. Structural design

Butt-welding flange: flange and pipe are welded by beveling, the flange neck is longer, the connection is more solid and the integrality is stronger.

Flat welding flange: flange and pipe are welded by lap welding, the neck of flange is shorter or no neck, simple structure.

6. Usage Scenario

Butt-welding flange: It is suitable for high pressure (above PN10), high temperature, or pipeline system that needs high sealing. Widely used in petroleum, natural gas, chemical industry, nuclear energy and other fields.

Flat welding flanges: suitable for medium and low pressure (below PN2.5), low temperature, non-critical piping systems. Mostly used in industrial pipelines, low pressure fluid transportation and other scenarios.

7. Installation method

Butt-welding flange: need to bevel the pipe and flange before installation, and then perform full weld-through welding, with higher process requirements and more complicated installation.

Flat welding flange: only simple welding on the outer wall of the pipe is required, with low process requirements and more convenient installation.

8. Sealing performance

Butt-welding flange: due to the high strength of welding structure, leakage can be effectively avoided, with superior sealing performance, suitable for high-demanding scenes.

Flat welding flange: due to the small welding area, the pressure-bearing capacity and sealing performance are weaker.

9. Cost

Butt-welding flange: Higher manufacturing and installation cost, but longer operation stability and service life.

Flat welding flange: lower manufacturing and installation costs, suitable for scenes with limited budget.

10. Stress resistance

Butt-welding flanges: smooth transition of welded joints reduces stress concentration and is more resistant to fatigue.

Flat welding flange: stress concentration is relatively more obvious, weaker fatigue resistance.

Choosing butt-welding flanges: if high pressure, high temperature and high sealing are required, give priority to butt-welding flanges.

Choose flat welding flange: if the pipeline pressure is low, the medium condition is relatively loose, and you need to save cost, you can choose flat welding flange.