AWWA C207 is the waterworks steel flange standard, and it is much simpler than the ASME standards it sits alongside. Four classes, four ratings. The complications come from what it shares with ASME rather than from the standard itself.
The four classes
| Class | Style | Water working pressure | Typical use |
|---|---|---|---|
| B | Flat ring, no hub | 86 psi | Low pressure distribution, gravity mains |
| D | Flat ring, no hub | 150 psi, and 175 psi in the smaller sizes | The workhorse. Most municipal and plant work |
| E | Hub flange | 275 psi | Higher pressure transmission, pump discharge |
| F | Hub flange | 300 psi | The heaviest C207 pattern |
Only B and D are ring flanges
This is the detail that gets lost. Class B and Class D are flat rings: plain steel annuli, no hub, no socket, slipped over the pipe OD and welded in place.
Class E and Class F are hub flanges. They have a raised hub like a conventional slip-on flange, which gives them more section and lets them carry the higher pressure.
So when someone says "C207 ring flange", they mean B or D, or they are using ring loosely to mean any C207 flange. On an enquiry it is worth asking which.
The drilling overlap
Class D drilling follows the ASME B16.1 Class 125 template, and that template is shared with ASME B16.5 Class 150. In many sizes a C207 Class D ring will bolt directly to a Class 150 steel flange.
Useful when tying water pipe into plant piping. Also the source of most of the trouble with these parts.
Bolting together is not being equivalent. Class D is rated for 150 psi of water. ASME B16.5 Class 150 carbon steel is rated considerably higher, and at temperature. The joint is only as strong as the weaker flange. Sharing a bolt circle tells you nothing about rating or thickness.
The face type problem at that joint
A C207 ring flange has a flat face. Most ASME flanges have a raised face. Bolt a flat ring to a raised face and the load concentrates on the raised annulus, which puts a bending moment into a flat plate that was not designed to take it.
Where that joint cannot be avoided, it needs a full face gasket so the load spreads to the bolt circle, and it needs the engineer to have looked at it. It is not a fitter's decision.
Fabrication notes
- Squareness. A ring flange has no hub to locate it on the pipe, so it is easier to tack out of square than a slip-on. Out of square means uneven gasket compression and a joint that weeps.
- Weld detail on the drawing. Fillet sizes and whether both sides are welded come from the standard and the project specification. Do not leave it to the fitter.
- Distortion. Thin large diameter rings pull out of flat as they are welded. Plan the sequence, and check flatness afterwards.
- Coating. Waterworks flanges are coated, and potable service needs a coating approved for potable contact. Weld areas need recoating after fabrication.
Past the tables
C207 covers a wide size range, wider than ASME B16.5, but penstock, intake and large transmission work still runs past it. At that point the flange is a drawing: outside diameter, thickness, bolt circle, hole count and size, and material. We cut flat rings from plate 1/4 inch through 8 inch thick and machine rings through 203 inches.
Identifying an existing flange
Retrofit work usually starts with an unmarked flange in the ground. Five measurements will normally identify it:
- Outside diameter of the flange
- Bolt circle diameter
- Number of bolt holes
- Bolt hole diameter
- Flange thickness, and whether there is a hub
Send those and we will tell you what it is and supply the match.
Full detail on AWWA C207 ring flanges, and note that waterworks projects frequently carry domestic origin requirements.