Guide
AWWA vs ASME flanges for data center water mains
Large data center water mains sit between two worlds: process piping, which uses ASME flanges, and waterworks, which uses AWWA flanges. Both appear on data center drawings. Knowing the differences avoids flanges that do not bolt up.
Use AWWA C207 (steel) or C228 (stainless) flanges on large water mains where the piping and valves follow waterworks standards. Use ASME B16.5 up to 24 inches and B16.47 above it where the project is specified to ASME, raised faces are wanted, or the joint sees more than water service.
The four standards
| Standard | Material | Sizes | Classes | Face |
|---|---|---|---|---|
| AWWA C207 | Steel | 4 to 144 in | B, D, E, F (86 to 300 psi) | Flat |
| AWWA C228 | Stainless steel | 2 to 72 in | SA, SB, SD, SE, SF (50 to 300 psi) | Flat |
| ASME B16.5 | Steel and alloys | 1/2 to 24 in | 150 to 2500 | Raised standard; flat optional |
| ASME B16.47 | Steel and alloys | 26 to 60 in | Series A 150 to 900; Series B 75 to 900 | Raised |
Pressure: how they compare
AWWA classes are water service ratings. Class D, the most common, is rated 175 psi up to 12 inches and 150 psi above. An ASME Class 150 flange in A105 is rated 285 psi at ambient temperature, with the rating falling as temperature rises. Most chilled water loops operate well below 150 psi, so either standard can work; the question is fit with the rest of the system.
Faces and gaskets
AWWA flanges are flat faced and use full-face gaskets. ASME flanges are normally raised face with ring gaskets. Mixing a raised face against a flat face concentrates bolt load and can crack cast iron or distort a light ring flange. More on faces.
Drilling
AWWA C207 Classes B, D and E are drilled to the ASME B16.1 Class 125 cast iron pattern, and Class F to Class 250. Up to 24 inches, Class 125 drilling matches ASME B16.5 Class 150. Above 24 inches, B16.47 Series A and Series B each have their own drilling, so check every mating valve and fitting on the drawings.
Large butterfly valves and fittings are bought to one flange standard. Pick the flange standard that matches them, then order the pipe flanges to suit.
When to use which
| Situation | Better fit |
|---|---|
| Condenser water main, 36 in, waterworks valves | AWWA C207 Class D |
| Stainless facility water main, 30 in | AWWA C228 Class SD |
| Chilled water header, 30 in, ASME project specification | ASME B16.47, series to match valves |
| Pump or chiller connection, 12 in, cast iron casing | ASME B16.5 Class 150 flat face |
| Any line up to 24 in on an ASME project | ASME B16.5 Class 150 |
Frequently asked questions
Is an AWWA C207 Class D flange weaker than ASME Class 150?
It is rated lower, 150 to 175 psi for water against 285 psi for an A105 Class 150 flange at ambient temperature, and it is lighter. For a chilled water or condenser water main operating below 150 psi, Class D is adequate.
Can AWWA and ASME flanges be bolted together?
Up to 24 inches, AWWA C207 Classes B, D and E share bolting with ASME B16.1 Class 125, which matches ASME B16.5 Class 150. Faces differ, so the ASME flange should be flat faced at that joint. Above 24 inches, compare drilling on the drawings before mixing standards.