Flanges by standard
ASME B16.5 flanges for data center piping
ASME B16.5 covers steel pipe flanges from NPS 1/2 to 24. It is the default flange standard for data center mechanical piping in North America, the Middle East and most of Asia, almost always in Class 150.
For data center water piping up to 24 inches, specify ASME B16.5 Class 150 flanges: raised face between steel parts, flat face against cast iron, weld neck or slip-on, in A105 on the facility side and 316L or 304L on stainless loops.
What the standard covers
ASME B16.5, Pipe Flanges and Flanged Fittings, sets dimensions, tolerances, marking, materials and pressure-temperature ratings for steel flanges from NPS 1/2 to NPS 24. It defines seven pressure classes: 150, 300, 400, 600, 900, 1500 and 2500. Above NPS 24, flanges move to ASME B16.47.
A flange's class is not its working pressure. The allowable pressure depends on the material group and the temperature, and falls as temperature rises. Data center water loops run cool, so they sit at the top of the rating tables.
Ratings for data center materials
| Group | Materials | Class 150 | Class 300 |
|---|---|---|---|
| 1.1 | A105, A350 LF2 | 19.6 bar (285 psi) | 51.1 bar (740 psi) |
| 2.1 | A182 F304 | 19.0 bar (275 psi) | 49.6 bar (720 psi) |
| 2.2 | A182 F316 | 19.0 bar (275 psi) | 49.6 bar (720 psi) |
| 2.3 | A182 F304L, F316L | 15.9 bar (230 psi) | 41.4 bar (600 psi) |
Most chilled water loops operate well below 150 psi (about 10 bar). Class 300 appears where static head is large, for example the lowest floors of a multi-storey data center, or where a project standard requires it on pump discharges.
Class 150 dimensions
Bolt circles and bolting for the sizes most used in data center plant rooms and white space. All Class 150 flanges of a given size share these dimensions regardless of type or material.
| NPS | DN | Flange OD | Bolt circle | Bolts | Bolt size |
|---|---|---|---|---|---|
| 1/2 | 15 | 3.50 | 2.38 | 4 | 1/2 |
| 3/4 | 20 | 3.88 | 2.75 | 4 | 1/2 |
| 1 | 25 | 4.25 | 3.12 | 4 | 1/2 |
| 1 1/2 | 40 | 5.00 | 3.88 | 4 | 1/2 |
| 2 | 50 | 6.00 | 4.75 | 4 | 5/8 |
| 2 1/2 | 65 | 7.00 | 5.50 | 4 | 5/8 |
| 3 | 80 | 7.50 | 6.00 | 4 | 5/8 |
| 4 | 100 | 9.00 | 7.50 | 8 | 5/8 |
| 6 | 150 | 11.00 | 9.50 | 8 | 3/4 |
| 8 | 200 | 13.50 | 11.75 | 8 | 3/4 |
| 10 | 250 | 16.00 | 14.25 | 12 | 7/8 |
| 12 | 300 | 19.00 | 17.00 | 12 | 7/8 |
| 14 | 350 | 21.00 | 18.75 | 12 | 1 |
| 16 | 400 | 23.50 | 21.25 | 16 | 1 |
| 18 | 450 | 25.00 | 22.75 | 16 | 1 1/8 |
| 20 | 500 | 27.50 | 25.00 | 20 | 1 1/8 |
| 24 | 600 | 32.00 | 29.50 | 20 | 1 1/4 |
Up to NPS 24 these dimensions match ASME B16.1 Class 125 cast iron flanges, which is why steel Class 150 flanges bolt directly to cast iron chillers, pumps and valves. Mate them with a flat face and a full-face gasket.
Flange types and faces
| Type | Typical use |
|---|---|
| Weld neck | Pump, chiller and CDU nozzles; stainless TCS headers; anywhere the spec wants butt welds |
| Slip-on | Carbon steel chilled and condenser water mains where fillet welds are allowed |
| Blind | Header ends, future data hall connections, test and flushing points |
| Lap joint | Stainless systems with a stub end; skids that need bolt hole alignment |
| Socket weld, threaded | Vents, drains, instrument tappings up to 2 inches |
The Class 150 raised face is 1.6 mm (0.06 in) high and has the standard serrated finish unless you specify otherwise. Tell us if your gasket supplier needs a particular face finish.
How to write the line item
A complete B16.5 description lets us quote without questions. Use this order:
Flange, weld neck, RF, NPS 6, Class 150, bore Sch 10S, ASTM A182 F316L, ASME B16.5, pickled and passivated, EN 10204 3.1, qty 24
Our flanges are marked to the same pattern: RIC, specification, grade, size, class and lot number, which ties each flange to its EN 10204 3.1 certificate.
Frequently asked questions
Is Class 150 enough for data center chilled water?
Usually, yes. Most chilled water loops operate well below 150 psi, and an A105 Class 150 flange is rated 19.6 bar (285 psi) at ambient temperature. Check the lowest point of a tall building, where static head is added to pump pressure, and the design temperature if the loop carries warm water.
Do ASME B16.5 Class 150 flanges bolt to Class 125 cast iron?
Up to NPS 24 the bolt circle, bolt count and bolt size match ASME B16.1 Class 125. Use a flat face steel flange and a full-face gasket against cast iron.
Which bore should a weld neck flange have?
The bore of a weld neck flange must match the inside diameter of the pipe it is welded to, so state the pipe schedule on the order, for example Sch 10S for stainless or STD for carbon steel.
Can you supply the bolts with the flanges?
Yes. Our ISO 9001 scope covers the supply of fasteners, so matching stud bolts and nuts can be quoted with the flanges.