The maximum working pressure of an ASA Class 300 flange (which is equivalent to ASME B16.5 Class 300) depends entirely on the material of the flange and the operating temperature of the system.
The "300" designation is a pressure class number, not a fixed pressure value in PSI or bar across all temperatures.
The following values are based on non-shock pressure and temperature ratings for common materials, per the ASME B16.5 standard:
Temperature Range (°C)
Carbon Steel (e.g., ASTM A105) Max Pressure
Stainless Steel (e.g., ASTM A182 F304/F316) Max Pressure
-29°C to 38°C (Ambient)
51.1 bar (approx. 740 psi)
51.1 bar (approx. 740 psi)
100°C
46.2 bar
48.7 bar
200°C
38.3 bar
44.5 bar
300°C
33.1 bar
40.5 bar
400°C
22.1 bar
37.3 bar
In summary: At standard ambient temperatures (up to 38°C), a Class 300 flange made of carbon or stainless steel can handle approximately 51.1 bar (740 psi). The pressure rating decreases as the temperature increases, so you must reference the specific pressure-temperature chart for the material
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