What are the classifications of flanges?

Flanges can be classified in various ways, mainly based on different dimensions such as connection method, sealing surface, pressure level, material, standard, shape, and purpose. The following are common classification methods and key points:

1. Classification by connection method

- Welded flange

- Butt welding flange (WN): high-strength connection, used for high-pressure and high-temperature pipelines.

- Flat welding flange (SO): low cost, suitable for low pressure and normal temperature.

- Socket welding flange (SW): small-diameter pipeline, good sealing.

- Threaded flange (Threaded): connected by thread, used for low pressure and non-corrosive media.

- Lapped joint flange (Lapped joint): The flange can be rotated for easy installation, and is often used for corrosive media (the flange and the pipe material can be different).

2. Classification by sealing surface type

- Flat surface (FF): low pressure, non-harsh working conditions (such as normal temperature water pipes).

- Raised surface (RF): most common, medium and low pressure sealing (such as chemical pipelines).

- Concave and convex surface (MFM): concave and convex fit, more reliable sealing.

- Tenon and groove surface (TG): tenon and groove fit, used for high pressure and leaky media.

- Ring joint surface (RTJ): metal ring gasket seal, dedicated to ultra-high pressure (such as oil drilling).

3. Classification by pressure level

- Low pressure flange: PN6/PN10 (national standard), Class 150 (American standard).

- Medium pressure flange: PN16/PN25, Class 300.

- High pressure flange: PN40/PN64, Class 600/900.

- Ultra-high pressure flange: PN100/PN160, Class 1500/2500.

4. Classification by material

- Carbon steel: Q235, 20# steel, general economic material.

- Stainless steel: 304/316L, corrosion-resistant, used in food and chemical industry.

- Alloy steel: 16Mn, Cr-Mo steel, resistant to high temperature and high pressure (such as power plant boilers).

- Plastics: PVC, PP, mildly corrosive, low-pressure environment.

5. Classification by standard system

- National standard (GB): such as GB/T 9119 (steel flange).

- American standard (ASME): ASME B16.5 (commonly used), B16.47 (large diameter).

- European standard (EN): EN 1092-1 (incorporated into German standard DIN).

- Japanese standard (JIS): JIS B2220 (commonly used in chemical industry).

6. Classification by shape

- Circular flange: standard shape, accounting for more than 90% of applications.

- Square/rectangular flange: special scenes such as ventilation ducts.

- Special-shaped flange: customized design (such as oval).

7. Classification by use

- Pipe flange: connecting pipeline system.

- Equipment flange: connecting reactors, storage tanks and other equipment.

- Blind flange: Block the end of the pipeline for easy maintenance.

8. Classification by manufacturing process

- Forged flange: High strength, suitable for high pressure (such as petrochemical pipelines).

- Cast flange: Low cost, but may have pore defects (low pressure use).

- Rolled flange: Large diameter flange, made by rolling and welding steel plates.

9. Special function flanges

- Rotating flange: Adjustable angle to compensate for installation errors.

- Reducing flange: Connect pipes of different diameters.

- Insulating flange: Prevent electrochemical corrosion (such as long-distance buried pipelines).

Key factors in selection

- Medium characteristics: Corrosiveness and toxicity determine the material (such as stainless steel or plastic lining).

- Working conditions: Pressure and temperature determine the type of sealing surface (such as RTJ for high pressure).

- Installation and maintenance: Whether frequent disassembly is required (select loose flange).

After mastering the classification logic, you can further select the model in combination with the parameter table of specific standards (such as ASME or GB).