I. Two core parameters of flanges
1. Nominal diameter (DN)
The nominal diameter is a standardized designation for the inside diameter of the pipe to which the flange connects, expressed in millimeters (mm). For example, DN50 indicates that the flange fits a pipe with an inside diameter of approximately 50 mm. According to the national standard GB/T 9119, the DN range is from DN15 (small diameter) to DN4000 (extra large diameter). The actual inside diameter may vary slightly due to wall thickness.
2. Nominal pressure (PN)
The nominal pressure is the maximum allowable working pressure of the flange at 20°C, expressed in MPa (megapascals). Common grades include PN6, PN10, and PN16. For example, a PN16 flange can withstand a pressure of 16 MPa. American standards (such as ANSI B16.5) use the term "Class" to indicate pressure; for example, Class 150 corresponds to approximately 2.0 MPa.
II. Detailed Explanation of Other Key Parameters
1. Sealing Surface Type
- Raised Face (RF): Most commonly used, with a raised sealing ring on the surface, suitable for medium and high pressures (PN10-PN40).
- Full Face (FF): Flat, without raised surfaces, mostly used for low pressures (PN6 and below) or gasket seals.
- Ring Joint (RTJ): With an annular groove, used for high-pressure and high-temperature conditions (e.g., Class 600 and above).
2. Flange Standards and Materials
- Standards: National Standard (GB/T), American Standard (ANSI), European Standard (EN), Japanese Standard (JIS), etc., with significant dimensional differences between different standards.
- Material: Carbon steel (Q235), stainless steel (304/316), alloy steel, etc. The selection should consider the corrosiveness of the medium and the temperature.
3. Number and Diameter of Bolt Holes
The number of bolt holes in a flange is related to the nominal diameter. For example, a DN100 flange typically has eight bolt holes with a diameter of 18 mm (GB/T standard). Bolt specifications must match the pressure rating to avoid leakage risks.
III. Parameter Selection Example
Using a chemical pipeline as an example:
- Operating Conditions: Steam transportation, pressure 1.2 MPa, temperature 180°C.
- Selection: DN200 PN16 RF flange (GB/T 9119), material 304 stainless steel, bolt holes 12 x Φ22 mm.
Professional Reference:
- Nominal diameter and pressure values are based on GB/T 9119-2010, "Plate-Type Slip-On Steel Pipe Flanges."
- American Standard pressure ratings refer to ASME B16.5-2020.
The above parameter combinations ensure flange sealing, strength, and system compatibility. In actual applications, a comprehensive assessment must be made based on the media c