Why Rubber Gasket inside diameter is more than flange bore?

[7016]

Hi,
I have gone through the various gasket standards EN 1514-1, ASME-B-16.20, ASME-B-16.21. And observed that inside diameter of gasket is more than the bore of the flange. Please find the attachment for easy understanding.

I don't understand why the inside diameter of gasket is more than the flange bore in all these standards!!!

To my knowledge, When gasket ID was sized larger than the flange ID, the gap that would be left from flange to flange, where the gasket is void, would cause increased turbulent flow of the media. An increase of turbulent flow leads to elevated rates of corrosion and erosion, which would take place on the flange faces. To go along with this problem, there would be an increase of unwanted media build-up, or fluid trap in this void.

Anyone please clarify my about doubt.

 

[3DDave]

What does the flange look like? Is there any anti-crush feature to prevent over-compression of the gasket?

 

[LittleInch]

Unless these are flat face flanges then the would be a gap even if the gasket was exactly the same as the bore of the flange.

In any event the ID of the pipe and flange can change depending on the material, pressure and temperature.

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

 

[bcd]

To ensure correct positioning at assembly, the flange gaskets are centered on the OD. Either by the flange bolts or flange raised face. Then the required gasket area in order to achieve the desired contact stress determines the gasket ID.

It is not possible to ensure the gasket is properly centered at assembly and not projecting into the waterway if you try to center at the ID.

How much turbulence, corrosion, and unwanted media build-up do you believe happens? Is it any worse than what will occur in the valves, fittings, and other components in the pipeline?