Standards Reference
AWWA C207 and C228: Waterworks Flanges
If your line is moving water, AWWA is almost certainly your standard. C207 covers steel pipe flanges for waterworks service from 86 psi all the way through 300 psi. C228 covers their stainless steel counterparts. Together they cover municipal distribution, treatment plants, transmission mains, pump stations, cooling water, fire protection, and the lightweight steel flange family that has become the default for utility-grade piping.
AWWA C207 Pressure Classes
C207 organizes steel flanges into four pressure classes. The class determines working pressure, flange thickness, and where the flange is appropriate in the system. Classes B, D and E are defined from 4 inch through 144 inch. Class F covers 4 inch through 48 inch.
| Class | Working Pressure | Size Range | Typical Service |
|---|---|---|---|
| Class B | 86 psi | 4" - 144" | Low-pressure water distribution |
| Class D | 175 psi (sizes thru 12") 150 psi (over 12") | 4" - 144" | Standard waterworks service |
| Class E | 275 psi | 4" - 144" | Higher-pressure transmission mains |
| Class F | 300 psi | 4" - 48" | High-pressure industrial water |
Note: Class D has a stepped working pressure. Through 12 inch the rating is 175 psi. From 14 inch through 144 inch the rating drops to 150 psi. This catches engineers who assume a single rating across the whole size range.
Class 125LW Steel Flanges: The Workhorse
Class 125LW (Lightweight) flanges are widely specified in waterworks, and the reason has very little to do with water pressure and everything to do with bolt patterns.
A Class 125LW steel flange has the same outside diameter, same bolt circle, and same number and size of bolt holes as a corresponding ANSI B16.1 Class 125 cast iron flange. That dimensional match is the whole point. It lets a steel flange bolt up directly to a cast iron valve, pump, strainer, or existing section of cast iron pipe without an adapter or a custom drill.
What makes 125LW different from a B16.5 Class 150 is the cross-section. The flange is thinner and lighter, which keeps cost and weight down. 125LW is properly part of the ASME B16.1 lightweight family - the standard applies AWWA-style material allowances (typically ASTM A36 plate or A105 forgings) to the B16.1 lightweight dimensional pattern. AWWA C207 is a separate waterworks specification with its own pressure classes; the two overlap in drilling but they are not the same standard.
Class 125LW dimensions are published from 4 inch through 96 inch in the Texas Flange Class 125LW table. For higher-pressure service, AWWA C207 Class E and Class F flanges fill the gap between 125LW and the heavier B16.5 classes.
For more on the bolt pattern compatibility, see the ANSI B16.1 reference page.
AWWA C228: Stainless Steel Waterworks Flanges
C228 is the stainless steel counterpart to C207. It applies the same dimensional and pressure-class framework to stainless flanges intended for waterworks service, with material requirements that address corrosion in aggressive water environments.
Common materials per C228 include 304/304L and 316/316L austenitics. The standard is increasingly specified on potable water projects where lead-free certification, chloride resistance, and long service life justify the up-front material premium over carbon steel.
See stainless steel materials for the grades commonly used in C228 service.
Materials Used Under AWWA C207
ASTM A36
Common plate-cut material for blind flanges and large diameter slip-on rings. Carbon steel, weldable, cost-effective. The default for Class B and Class D plate flanges.
ASTM A516-70
Pressure vessel quality plate. Specified for higher-pressure blinds and large diameter flanges where notch toughness and weldability matter. Common on Class E and Class F.
ASTM A105
Carbon steel forging used where the flange is forged rather than cut from plate. Common on smaller bore weld neck and slip-on Class 125LW flanges.
Where AWWA Flanges Go to Work
Municipal Water and Wastewater
- Treatment plant headers and process piping
- Distribution mains and transmission lines
- Pump station suction and discharge
- Aeration and clarifier piping
- Chemical feed lines (with appropriate liner or alloy)
- Reservoir and tank connections
Industrial Water Service
- Cooling tower intake and discharge
- HVAC chilled water and condenser water
- Fire protection mains and riser headers
- Plant utility water distribution
- Boiler feedwater (low-pressure side)
- Power plant circulating water
For more on waterworks flange configurations, see the Texas Flange flange types page or the Texas Flange waterworks flanges page.
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