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Why flat face flange in water service? 4
- Thread starter onrush
- Start date
They're typically used- you might equally well ask why raised face are used elsewhere.
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.
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.
As JStephen suggests I think it is historical dating back to use of cast iron flanges and heavy handed labourers. When I started with a water board in UK in the 1960's our specification was always for full face gaskets - "internal rings shall not be used". I guess they are still using the same specification.
I think it is cost. On a RF flange you typically use an expensive flex gasket. On a FF flange you use a paper gasket. Pressures on "water systems" tend to be lower and water is an easier fluid to capture than steam or other gases so the cheeper gasket is reasonable.
On high-pressure water systems (like a water flood in an oil field) the flanges are all RF.
David Simpson, PE
MuleShoe Engineering
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On high-pressure water systems (like a water flood in an oil field) the flanges are all RF.
David Simpson, PE
MuleShoe Engineering
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
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2
- #6
onrush,
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!
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!
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2
- #7
Cast iron flat face flanges are the reason.
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.
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.
b]zd4as[/b] hit close to the one of the main reasons, the gasket normally used for say AOW service. The normal gaskets were red rubber, leather, or some asbestos and none required very high seating stress. In fact a RF flange will tend to cut the gaskets except the asbestos and the gaskets tended to be reused or were in service for extended periods. The other is that the normal bolting was cold rolled carbon steel and the bolt stress levels were 7,500-30,000 psi. The norm was 20,000 psi. The full face gasket was also used to prevent a bending moment on the CI flanges.
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.
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.
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