Seal face of flanges B16.5 RF / gasket B16.21

[Stefan2211]

Dear All,

can someone provide me with a technical explanation why the flange seal face is not fully utilized by the gasket. I know the dimensions for the shown flange 3" RF 150 and the gasket 3" are both correct acc to the ASME code.
What is the reason not matching the inner diameter of the flange? The gaskets is centered by the outer diameter so the position is more or less fixed.
Thanks

 

[1503-44]

Wall thickness varies.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[LittleInch]

Can you draw a diagram?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Stefan2211]

1503-44
The dimesnion of the gasket 3"-150 is ID 3.5" (89mm) However, the flange 3"-150 ID is 77mm. Yes I agree you can have pipes 3" with extra thick wall thickness but the flange remains the same.

 

[LittleInch]

Also you have shown a WN flange.

A 3" slip on flange has a bore of 90.7mm so in that case the inner RF diameter cannot be more than the bore of the flange. No one wants to have two or three different sized 3" gaskets hanging around or any calculations varying because the type of flange changes and you don't want unused gasket hanging into the bore of the pipe as its not doing anything for anyone.

Gasket sealing is an art as there are many competing elements. Bolt force / flange force needs to be within the limits of the bolts and the flange material, but as high as possible.

Gasket material to seal should be a soft as possible to be squeezed between the flanges and even out any bumps or undulations / bits of grit. There is a happy medium but the surface area of the flange plays a part in that as well.

But the key is only having ONE size of 3" gasket to it all sized of 3" B16.5 flanges.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Stefan2211]

LittleInch,

good explanation. Thanks