Flange rating is usually expressed as “Class” or “PN”:
Flange Systems Are:
ANSI/ASME (American Standard) uses Class to indicate common grades: 150, 300, 600, 900, 1500, 2500
ISO/EN (European Standard) uses PN to indicate common grades: PN6, PN10, PN16, PN25, PN40
GB (Chinese Standard) uses PN to indicate the same as European Standard: PN6, PN10, PN16, PN25, PN40
Flange ratings are also called pressure ratings. Generally speaking, the higher the rating, the greater the pressure it can withstand and the better the durability. Below, we will discuss ratings and choosing the right flange for your application.
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Flange Class
ASME pressure ratings consider various pressure and temperature levels and are usually divided into 7 levels: 150, 300, 400, 600, 900, 1500, and 2500. The level indicates the maximum allowable pressure at the same temperature. For example, a 400-level flange can withstand greater pressure and is heavier than a 300-level flange. For example, for a given material at a certain temperature, the safe working pressure of a 300-level flange is 300PSI (20.6 Bar).
The choice of flange grade is also related to the selected material:
Carbon steel flange (A105) is generally suitable for medium and low-pressure systems
Stainless steel flange (ss304, ss316) is generally suitable for food, medicine, and the chemical industry because of its corrosion resistance.
Alloy steel (F11, F22) suits high temperature and high-pressure environments.
Select a rating by referring to a standard table:
Flange ratings are established by organizations such as the American National Standards Institute (ANSI) and the American Society of Mechanical Engineers (ASME) to ensure that flanges and their associated piping systems are compatible and can safely handle the required operating conditions.
3. Simplified comparison table (ASME A105 carbon steel flange)
Class Grade Maximum allowable pressure (MPa) @ 200℃ Recommended use
| Class 150 | 1.43 | Low-pressure pipeline |
|---|---|---|
| Class 300 | 3.57 | Medium pressure |
| Class 600 | 7.14 | High temperature medium pressure |
| Class 900 | 10.71 | High temperature,High pressure |
| Class 1500 | 17.13 | Ultra-high pressure |
| Class 2500 | 28.45 | Special working conditions |
(This value is for reference only. Please verify the specific selection according to the standard table)
For example:
If you use ASTM A105 carbon steel flanges with a working pressure of 1.6 MPa at 200°C, then Class 150 or Class 300 is sufficient.
If the temperature rises to 400°C, you may need to choose Class 600 or even higher.
For more flange-related questions, please view related articles, such as the matching A53 pipe specifications, the advantages of ASTM A53 steel pipes, and the advantages of ASTM A106 steel pipes. Or you can directly contact Jizhong’s sales staff to help you answer questions about product selection and use for free.
