Flanges by type
Flat face flanges for chillers, pumps and cast iron valves
Many chillers, pumps, strainers and valves in a data center plant room have cast iron flanges with a flat face. Bolting a raised face steel flange to them can crack the casting. The fix is a flat face steel flange and a full-face gasket.
Wherever a steel pipe meets cast iron, ductile iron, fibreglass or plastic equipment in a data center plant room, order the steel flange flat faced and use a full-face gasket.
Why raised face and cast iron do not mix
A raised face concentrates gasket load on a ring inside the bolt circle. Against a flat cast iron flange, that leaves a gap at the bolts. As the bolts are tightened, the outer edge of the cast iron flange is bent toward the gap, and cast iron, being brittle, can crack. A flat face steel flange with a full-face gasket spreads the load across the whole face. ASME B31.1 makes this the rule for joints to cast iron flanges, and the same practice applies to building services piping.
Where flat face flanges appear
| Equipment | Typical flange |
|---|---|
| Chillers with cast iron water boxes | B16.1 Class 125 FF; mate with B16.5 Class 150 FF |
| End suction and split case pumps | Cast iron Class 125 FF or ductile iron |
| Strainers, check valves, butterfly valves | Often Class 125 FF drilling |
| Cooling tower connections | FRP or plastic flanges, flat faced |
| AWWA waterworks valves and pipe | AWWA C207 / C228, flat faced |
Up to 24 inches, ASME B16.1 Class 125 and ASME B16.5 Class 150 share the same bolt circle and bolting, so a Class 150 flat face steel flange bolts straight to Class 125 cast iron.
Write "FF" on the line item, for example: Flange, weld neck, FF, NPS 8, Class 150, ASTM A105, ASME B16.5. Full-face gaskets and matching bolting complete the joint.
Frequently asked questions
Can a raised face flange be machined to flat face?
Yes. Machining off the raised face is a common way to produce a flat face flange, as long as the remaining flange thickness meets the standard. It is better to order flat face flanges from the start.
Which gasket goes with a flat face flange?
A full-face gasket that covers the whole flange face and has bolt holes, such as EPDM rubber or compressed non-asbestos fibre for water service.
Do cooling tower connections need flat face flanges?
Often. Cooling tower basins and piping may be fibreglass (FRP) or plastic with flat-faced flanges. Bolt steel flat face flanges to them with full-face gaskets and the tower maker's torque values.