Steel Flange Types and Their Role in Industrial Piping Systems

Steel flanges are essential components used to connect pipes, valves, pumps, and other equipment, creating a robust yet flexible piping system. They allow easy disassembly and reassembly for maintenance or inspection—a critical requirement across most industries.This article details the most common types of steel flanges, their specific manufacturing methods, and the inherent advantages of each design.

1. Weld Neck Flanges

Weld neck flanges are easily recognized by their elongated tapered “neck” (hub), which is butt-welded directly to the pipe end. This structure ensures optimal stress distribution between the pipe and the flange.

Manufacturing Method

Weld neck flanges are almost always produced by hot forging.A heated steel billet or bar is shaped under pressure in a forging die to obtain the desired geometry.

The forging process aligns the steel grain structure to follow the contour of the flange, providing superior mechanical strength and excellent structural integrity—especially in the critical neck area.

After forging, machining operations (turning) are performed to finish the sealing faces and final dimensions.

Advantages

• High integrity: Ideal for critical applications involving extreme pressures and temperatures.

• Stress reduction: The tapered design ensures a smooth transition of wall thickness from hub to pipe, reducing stress concentration.

• Reliable sealing: The butt weld can be easily radiographically inspected for defects.

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2. Slip-On Flanges

Slip-on flanges are designed to slide over the pipe end before being welded at two points (inside and outside) to secure them in place.

Manufacturing Method

Similar to weld neck flanges, they are frequently produced through hot forging, although for larger sizes or low-pressure applications they may also be cut from steel plate.The bore is then machined on a lathe to ensure proper tolerances.

Advantages

• Easy installation: Easier to align and install than weld neck flanges, requiring less precision in pipe cutting.

• Cost-efficient: Faster fabrication and installation make them an economical choice for moderate-pressure and low-temperature applications.

3. Blind Flanges

Blind flanges are solid disks used to completely close off the end of a piping system, a valve, or a vessel opening. They have no central bore.

Manufacturing Method

Blind flanges are produced using the same methods as slip-on flanges: hot forging or plate cutting.Since they do not require machining a bore, the process is relatively simple, focusing mainly on finishing the sealing face.

Advantages

• Maximum sealing: Fully blocks flow—essential for pressure testing (hydrostatic).

• Versatility: Can be removed later to extend or modify the piping system.

• High pressure resistance: The solid structure handles significant mechanical and pressure loads.

4. Threaded Flanges

Threaded flanges have a conical internal thread (typically NPT, depending on standards) that screws onto a male-threaded pipe.

Manufacturing Method

These are also produced through hot forging, with the key manufacturing step being the precision internal threading performed by turning or milling.

Advantages

• No welding required: Ideal in fire-hazard zones where welding on-site is restricted.

• Reusable: Can be easily disassembled and reused.

• Specific applications: Used in utility systems with low-to-medium pressure—compressed air, water, and small-diameter piping.

5. Lap Joint Flanges

Lap joint flanges consist of two components:

• a loose flange (flange ring) that rotates freely, and

• a separate stub end welded to the pipe.

Manufacturing Method

The stub end is manufactured similarly to an elbow, typically forged and machined.The loose flange ring is forged or cut from plate with a larger inner diameter to allow free rotation.

Advantages

• Easy alignment: Because the flange rotates freely, bolt hole alignment is simple, even when the stub end is fixed.

• Material savings: In systems with expensive alloys (e.g., stainless steel), only the stub end requires corrosion-resistant material, while the loose flange can be carbon steel.

Using steel flanges ensures exceptional mechanical strength, resistance to extreme temperatures, and an extended service life for industrial installations.