ASME B31.9 building services piping: what it means for flanges
In North America, the chilled water, condenser water and facility water piping of a data center is usually designed to ASME B31.9, the building services piping code. Here is what it covers and how it shapes the flange order.
ASME B31.9 covers building services piping such as heating and cooling water in industrial, institutional, commercial and public buildings, for nonflammable liquids up to 350 psig (2,415 kPa) and 250 °F (121 °C). Data center water loops sit well inside those limits, so ASME B16.5 Class 150 steel flanges are the normal choice, with flat face flanges where the pipe meets cast iron, and every system is proven by a hydrostatic test at 1.5 times its design pressure.
What B31.9 covers
| Service | Maximum pressure | Temperature range |
|---|---|---|
| Nonflammable liquids, including heating and cooling water | 350 psig (2,415 kPa) | 0 to 250 °F (-18 to 121 °C) |
| Steam and steam condensate | 150 psig (1,035 kPa) | 0 to 366 °F (-18 to 186 °C) |
| Air, gases and vapors (nontoxic, nonflammable) | 150 psig (1,035 kPa) | 0 to 200 °F (-18 to 93 °C) |
The code applies within the property limits of industrial, institutional, commercial and public buildings and multi-unit residences. It does not cover refrigeration piping, potable water, sanitary and storm drainage, fire protection, or fuel piping beyond what it lists. Piping outside these limits moves to ASME B31.1 or B31.3.
Where data center loops sit
| Loop | Typical pressure | Typical temperature | Within B31.9 limits |
|---|---|---|---|
| Chilled water | Under 150 psi in most buildings | 40 to 60 °F supply | Yes |
| Condenser water | Low, open loop to towers | 80 to 100 °F | Yes |
| Facility water for liquid cooling | Under 150 psi in most buildings | Up to 113 °F at ASHRAE class W45 | Yes |
| Technology cooling system | Low, set by the CDU | Warm water, below the facility water class limits plus approach | Yes |
Flanges under B31.9
- Steel flanges: ASME B16.5 up to NPS 24, ASME B16.47 above. Class 150 covers almost every data center loop; check the rating at temperature with the pressure class guide.
- Cast iron interfaces: chillers, pumps and valves with ASME B16.1 Class 125 flanges mate with flat face steel flanges and full face gaskets.
- Large water mains: AWWA C207 flanges appear on large mains where the engineer of record accepts them.
- Materials: listed specifications such as ASTM A105 for carbon steel forgings and ASTM A182 F304L and F316L for stainless.
- Marking: flanges carry the maker, material grade, size and class, and the heat or lot number that ties each piece to its certificate. Reading the certificate that matches the marking.
B31.9 calls for a hydrostatic test at 1.5 times the design pressure or more, held for at least 10 minutes. ASME B16.5 allows flanged joints to be tested in the system at up to 1.5 times their 100 °F (38 °C) rating, rounded up to the next 25 psi. For a 316L Class 150 joint that is 350 psi; for A105 Class 150 it is 450 psi.
Beyond the code
B31.9 sets a minimum. Data center owners add their own rules, mostly for the technology cooling system: stainless pipework, purged welds, pickled and passivated surfaces, flushing and filtration targets. Those come from the owner's specification and guidance such as the Open Compute Project's TCS pre-commissioning guidelines. TCS flushing and cleaning.
Frequently asked questions
Is data center cooling water piping designed to B31.9 or B31.3?
In North America, chilled water, condenser water and facility water piping in data centers is usually building services piping under ASME B31.9, or under the local mechanical code that points to it. Some owners apply stricter rules from their own specifications to the technology cooling system, but the pressure and temperature still sit well inside B31.9.
Does B31.9 require EN 10204 3.1 certificates?
No. B31.9 asks for materials to recognized specifications such as ASTM A105 and A182; the type of certificate is set by the purchase order. Most data center projects ask for a mill test report or EN 10204 3.1 certificate, and every RIC order ships with one.
What test pressure does B31.9 use?
A hydrostatic test at 1.5 times the design pressure or more, applied at every point in the system and held for at least 10 minutes. ASME B16.5 flanged joints can take a system test at up to 1.5 times their 38 °C rating, rounded up to the next 25 psi.
Sources
- ASME B31.9, Building Services Piping: scope and service limits
- ASME B16.5, Pipe Flanges and Flanged Fittings: system hydrostatic testing
- National Institutes of Health, Office of Research Facilities, pipe testing guidance citing B31.9 (2019)
- ASHRAE TC 9.9, liquid cooling classes for facility water