Pressure rating is one of the most critical specifications of AWWA flanges for a waterworks or industrial pipeline system. A flange’s pressure class determines its ability to safely withstand internal system pressures over time without failure. The American Water Works Association (AWWA) provides detailed standards (AWWA C207 and AWWA C228) that define these classes, which apply to carbon steel and stainless steel flanges respectively.In this guide, we’ll break down the pressure classes defined by AWWA C207 and C228 standards, compare their specifications, and help you determine the right flange class for your specific application.
About Pressure Classes
A pressure class (also referred to as a pressure rating) defines the maximum working pressure a flange can handle safely, typically measured in pounds per square inch (psi). The pressure rating is affected by a few main factors:
Material type (carbon vs. stainless steel)
Flange dimensions
Operating temperature
Bolt pattern and gasket sealing surface
AWWA C207 Flange Pressure Classes (Carbon Steel)
AWWA C207 covers steel ring and blind flanges ranging from 4” to 144”. These flanges are categorized into four pressure classes, each designed for a specific pressure range and application environment. The materials conform to the requirements of AWWA C207 specifications but are typically ASTM A36 or A105 Grade C carbon steel. For blind flanges, AWWA recommends the use of Dish Assemblies for sizes above 48″.
| Class | Pressure Rating | Typical Sizes | Use Case / Notes |
|---|---|---|---|
| Class B | 86 psi | 4” to 144” | Low-pressure pipelines, treatment plants |
| Class D | 175 psi (1″–12″), 150 psi (14″–144″) | 4” to 144” | Mid-pressure municipal lines, water plants |
| Class E | 275 psi | 4” to 144” | High-pressure transmission, pump stations |
| Class F | 300 psi | 4” to 48” | Extreme pressure systems, critical infrastructure |
Example Applications:
Class B: Small facility connections
Class D: Municipal water mains
Class E: Long-distance water transfer pipelines
Class F: High-pressure industrial environments
AWWA C228 Flange Pressure Classes (Stainless Steel)
AWWA C228 standard covers stainless steel ring and blind flanges ranging from 2″ to 72″ (smaller sizes available when compared to C207). They are favored in corrosive, high-humidity, or chemical-laden environments. These flanges follow similar pressure classes but are designated with an “S” prefix to indicate stainless/alloy flange material. For blind flanges, AWWA recommends the use of Dish Assemblies for sizes above 48″. The materials conform to the requirements of AWWA C228 specifications but are typically 304L/316L Stainless Steel.
| Class | Pressure Rating | Typical Sizes | Ideal Environments |
|---|---|---|---|
| Class SA | 50 psi | 2″ to 14″ | Low-pressure, clean water |
| Class SB | 86 psi | 2″ to 60″ | Water distribution, general use |
| Class SD | 175 psi (1″–12″), 150 psi (14″–144″) | 2″ to 60″ | Treated water, wastewater |
| Class SE | 275 psi | 2″ to 72″ | Industrial water loops, tank connections |
| Class SF | 300 psi | 4″ to 48″ | Marine, chemical, high-pressure zones |
Example Applications:
Class SA: Groundwater systems, short-range potable pipelines
Class SB: Chlorinated water or municipal branches
Class SD: Desalination, water reuse, or UV disinfection systems
Class SE/SF: Chemical processing, marine intakes, high-salinity transfer lines
How to Select the Right Pressure Class
When you select a pressure class for your specific need, take into account the following factors:
| Factor | Why It Matters |
|---|---|
| Operating Pressure | Select a class rated above your system’s maximum pressure |
| System Size | Larger diameters (above 14″) may have slightly lower pressure ratings for Class D |
| Media Type | Clean water, wastewater, chemical, or seawater all affect material and class selection |
| Environment | Outdoor, buried, marine, or corrosive settings may require stainless steel (C228) |
| Maintenance Access | Remote or hard-to-access flanges should favor longer-lasting, corrosion-resistant options (e.g., Class SE or SF) |
AWWA Flange Pressure Class Summary
| Standard | Material | Class Options | Max Pressure |
|---|---|---|---|
| AWWA C207 | Carbon steel | B, D, E, F | 86 to 300 psi |
| AWWA C228 | Stainless steel | SA, SB, SD, SE, SF | 50 to 300 psi |
Final Thoughts
Understanding the pressure class of an AWWA flange is a very important factor in selecting the right components for your pipeline system. Our sales team at API can answer any questions about your flange requirements. Depending on its application, they can also recommend alternative products that may be better suited for your system. We also provide custom flange solutions tailored to your project specifications. Get connected with a dedicated sales representative today! Or call us: 503.692.3800