gasket design 1

[mielke]

can anyone refer me to a method on calculating the minimum gasket width.

For example I know we have a 1" flange with the gasket surface equaling the flange surface (thus we have a gasket with a 1" width). but when we put bolts in it we get a smaller gasket ligament. (ie a 1/2" bolt gives us somewhere less than a 1/4" gasket width.)

I am looking for a design method to understand the smallest ligament permissable.

Thank You

 

[pennpiper]

You don't calculate the minimum gasket width, you buy the proper gasket that fits the flange rating and facing you will use it with. The flange and the gasket must match. They are made that way.

You said you have a 1" flange. Okay
What Rating is this Flange?
What Facing is this Flange. Raised Face or Flat Face?

If you have a Flat face Flange then you might have a Class 125 or Class 250 Flange. If so then you would use a Full Face Gasket.

If you have a Raised Face Flange then you might have a Class 150, 300, 400 Flange. Then you would use a Raised Face Gasket.

Some of the dimensions affecting Gaskets (example: the O.D. of the Gasket face) for Class 150 through Class 400 are the same but it is always the safest thing to order the exact gasket to match your flange

 

[mielke]

we are designing a custom flange

 

[SnTMan]

mielke, it sounds like a full face design. We design these quite often. I am not aware of any real method for calculating the ligament, we typically use the "E" dimensions in TEMA Table D5 as the gasket half-width. Per this, for 1/2" bolt the E dimension is 5/8", gasket width is 1 1/4" and with a 5/8" hole, the ligament is 5/16".

I am not a big fan of full face gaskets. Manufacturing inaccuracies can easily reduce the ligament. The ligmament is the "real" gasket, the whole rest of it is just along for the ride, taking up bolt load without producing any sealing effect.

A more useful guideline might be the ASME B16.21 table for full face gaskets which have a wider ligament to the I.D. Make it as wide to the I.D. as you can.

Regards,

Mike