×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Why flat face flange in water service?
2

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?

RE: Why flat face flange in water service?

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.

RE: Why flat face flange in water service?

onrush,

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?

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.

RE: Why flat face flange in water service?

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
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?

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!


RE: Why flat face flange in water service?

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.

RE: Why flat face flange in water service?

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.       

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources