ASME Flange Pressure Classes: 150, 300, 600, 900, 1500 & 2500
ASME flange pressure classes indicate how much pressure a flange can safely withstand at a given temperature. Higher classes support higher pressures, thicker walls, and stronger bolting requirements. This guide gives a clear, beginner-friendly overview of pressure classes 150, 300, 600, 900, 1500, and 2500 and how they are selected in industrial piping.
ASME Pressure Class Diagram Coming Soon
What Is an ASME Flange Pressure Class?
A flange pressure class defines the maximum pressure-temperature rating of a flange according to ASME B16.5. The higher the class number, the stronger and thicker the flange. Pressure capability is affected by flange material, temperature, and gasket type.
Quick Comparison Table
| Class | Typical Use | General Pressure Range* |
|---|---|---|
| Class 150 | Low-pressure water, air, and utility service | Up to ~270 PSI |
| Class 300 | Moderate pressure, oil & gas, chemical service | Up to ~740 PSI |
| Class 600 | High-pressure systems & steam lines | Up to ~1480 PSI |
| Class 900 | Refineries & high-pressure oil pipelines | Up to ~2220 PSI |
| Class 1500 | Extreme pressure applications | Up to ~3700 PSI |
| Class 2500 | Ultra high-pressure systems | Up to ~6170 PSI |
*Approximate values at ambient temperature. Actual ratings depend on material and temperature.
How Pressure Classes Are Determined
ASME B16.5 defines pressure ratings based on:
- Flange material (carbon steel, stainless steel, alloy steel)
- Operating temperature
- Flange dimensions (thickness, bolt circle, hub size)
- Gasket type and seating stress
- Bolt size and material
As temperature increases, a flange's pressure capacity decreases.
This is why pressure–temperature charts are used to select the correct class.
When to Use Each Pressure Class
Class 150
- Water, air, HVAC, general utility service
- Low-pressure chemical systems
Class 300
- Oil & gas, chemical, and industrial service
- Moderate pressure pipelines
Class 600
- High-pressure steam
- Chemical and refinery lines
Class 900
- High-pressure crude & refined hydrocarbon service
- Offshore and subsea systems
Class 1500
- Extreme pressure systems
- High-temperature refinery applications
Class 2500
- Ultra high-pressure environments
- Specialized petrochemical or power generation systems
Conclusion
ASME flange pressure classes help ensure that a piping system can withstand the required pressure and temperature safely. Choosing the correct class protects system integrity, reduces maintenance costs, and ensures compliance with ASME standards. Always consult pressure–temperature charts and material specifications when selecting a flange class.