Gasket Calculation 1

[Jmoore1]

Does anyone know of a calulation provided by ASME to check whether a Gasket is the correct size?

I am doing a calculation as per ASME Sec VIII app 2, and I noticed there is no true failure mode for the gasket. (really the flange MAWP increases to no end with a thinner gasket due to seating stress and area)

Obviously if this were the only reason for choosing a gasket size we would have extremely small gaskets to increase the MAWP so a calculation must exist for a required gasket Od and ID.

Does anyone know of anything?

 

[SnTMan]

Jmoore1, no mandatory calculation. Table 2.4 recommended widths, and from the old days, Nmin calculation.

Nmin = Ab*Sa/(2*pi*G*y), nomenclature per Apx 2.

Checks against exceeding gasket seating stress, y.

Probably better is to find out the appllied stress recommended by the gasket manufacturer and size the gasket accordingly.

Regards,

Mike

 

[Jmoore1]

Is Nmin the min thickenss or minimum od-id?

 

[SnTMan]

Jmoore1, Nmin is the minimum width, corresponding to N in Appendix 2, 1/2(OD-ID).

Nothing on thickness as far as I know.

Regards,

Mike

 

[Jmoore1]

Is this Nmin calculation no longer there, ? the only nmin i can find is set for certain sizes (24-36) etc.

 

[SnTMan]

It was never part of Appendix 2 to my recollection, but was instead an "industry standard" type calculation.

It seems to me earlier versions of Codecalc did perform it, but the calculation was discontinued when Table 2.4 was introduced.

To expand on what I said earlier, the best way to size a gasket is to find out from the manufacturer the recommended applied stress, usually based on the actual gasket area (no b, bo) and the targeted actual bolt stress rather than design stress Sa / So.

Regards,

Mike