Why flat face flange in water service?
Why flat face flange in water service?
(OP)
Dear friends,
I really wonder why many project material specifications
require flat face (FF) flange in water service.
Is FF flange technically mandatory in water service or
just cost saving purpose?
I really wonder why many project material specifications
require flat face (FF) flange in water service.
Is FF flange technically mandatory in water service or
just cost saving purpose?





RE: Why flat face flange in water service?
I don't know for sure, but I have read or heard somewhere that raised face flanges shouldn't be used with cast iron flanges, as on valves, which would probably be the motivation. Of course, the "Cast iron" fittings nowadays are generally ductile iron, valves quite likely are, and this may not be that much of a concern anymore.
RE: Why flat face flange in water service?
Flat face is not mandatory in water service.
For flange Class 125, the cast iron valve (ASTM A126 Cl.B) comes with flat face (FF) flange.
You may change to cast steel valve (ASTM A216 WCB) with flange Class 150 raised face (RF).
RE: Why flat face flange in water service?
RE: Why flat face flange in water service?
On high-pressure water systems (like a water flood in an oil field) the flanges are all RF.
David Simpson, PE
MuleShoe Engineering
www.muleshoe-eng.com
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
The harder I work, the luckier I seem
RE: Why flat face flange in water service?
RF flanges are used to produce a tight flange joint. When you tighten the studs on a RF flange, the flanges cantilever because of the gap between them so that you are using the elasticity of the steel to produce a tighter joint.
If you use RF flanges on a brittle material such as cast iron, the cast iron flanges do not have the elasticity to bend, they can crack if you over torque the studs. FF flanges are used for brittle materials so that there is no gap between flanges.
I once had a contractor mate a cast iron gas regulator (with FF flanges) between RF steel flanges. The regulator cracked during installation and developed a major leak after several days of service. The building had to be evacuated. Had the contractor faced-off the RF flange before installation, the regulator would not have cracked.
Never mate a FF piping component with a RF pipe flange!
RE: Why flat face flange in water service?
In addition the quality of labour used in the water industry is not generally the same level as in the refinery and petrochem industry. A flat face flange gasket is easier to align using the bolts than a raised face.
RE: Why flat face flange in water service?
When I first started work we were still using reinforced Blue African Asbestos on flat face flanges in low pressure steam (175 psig). The gasket of choice was the same on higher pressure steam except there were RF Flanges until 500 psig and alloy bolting. Above this it was RTJs.