Non-metal Gasket Seating Stress
Non-metal Gasket Seating Stress
(OP)
Has anyone encountered the following Gasket type for a R.F. Welding Neck Flange:
“Non-metal Flat Ring, Tanged Graphite”
I am trying to do the flange leakage calcs on a raised face flange connection with this type gasket. One of the controlling parameters for this calc is the “Min. Design Seating Stress, y” of the gasket. So I went to ASME Sect. VIII - DIV I to look into Table 2-5.1 which lists Gasket factors & Contact facings for different type Gasket materials. Now my problem is that I could not tie this Gasket to any of the Gasket materials listed in the far left column of Table 2-5.1.
Does anyone know where I can access information on “Min. Design Seating Stress, y” & "Modulus of Elasticity of non-metal Gasket material"? What is "Tanged Graphite"? Is an equivalent material listed in Table 2-5.1? Any leads are appreciated.
Regards,
drno
“Non-metal Flat Ring, Tanged Graphite”
I am trying to do the flange leakage calcs on a raised face flange connection with this type gasket. One of the controlling parameters for this calc is the “Min. Design Seating Stress, y” of the gasket. So I went to ASME Sect. VIII - DIV I to look into Table 2-5.1 which lists Gasket factors & Contact facings for different type Gasket materials. Now my problem is that I could not tie this Gasket to any of the Gasket materials listed in the far left column of Table 2-5.1.
Does anyone know where I can access information on “Min. Design Seating Stress, y” & "Modulus of Elasticity of non-metal Gasket material"? What is "Tanged Graphite"? Is an equivalent material listed in Table 2-5.1? Any leads are appreciated.
Regards,
drno





RE: Non-metal Gasket Seating Stress
Not 100% but does the graphite part of 'Tanged Graphite' refer to the filling of a spiral wound steel gasket. For example, for a typical SS SW Graphite filled gasket the m factor is 3 and the y value is 5000psi. These values are usually available in a supplier catalogue.
Cheers,
J O'D
RE: Non-metal Gasket Seating Stress
Klinger also makes a tanged core graphite sheet but I don't have their book handy.
If you go to the Garlock website you should be able to find these numbers.
RE: Non-metal Gasket Seating Stress
I had reasoned myself into believing that graphite filling must have replaced asbestos due to its environment friendly attributes. I carried out my preliminary clacs based on the m (gasket factor) & y's (seating stress) listed for "Asbestos with suitable binder ..." in ASME sect. VIII Div. 1 (appendix 2). By interpolation I picked y=5000 psi & m=3 which was conservative for my purpose. Reducing 'y' to 3000 psi will certainly help me achieve more favorable results.
JohnOD & sjrfc2
I thank you both for your helpful comments.
regards,
drno
RE: Non-metal Gasket Seating Stress
I don't know if interpolation of the values in App 2 is valid based on moving to graphite from asbestos. I think those values are high because of the spiral wound design.
If you'd like to stick with spiral wound for ease of use, there may be some specialty spiral wounds that can help out with the minimum required seating stress. Flexitallic has a "LS" line (low stress) for applications like the 150 class flanges. I know Garlock markets an "Edge" gasket which is touted to limit required seating stress by controlling winding density (number of plies per inch) and also prevents buckling. From what I remember the Edge only had a slight improvement in seating load, dropping the y to 7500 with graphite filler. I think Flexitallic's LS gasket had a y of about 5000 but I'd encourage you to check with both of those manufacturer's.
There is some effect in switching filler metals on the spiral wounds. I think that going from graphite to teflon on the Edge gasket offered a reduction in y (I think from 7500 to 5000) but again you'd want to check with the manufactuer.
From a maintenance perspective, the spiral wounds are easy to work with and rugged. The tanged sheet graphite has to be cut (recommend die cut at a minimum), harder to clean flange surfaces after use and is more fragile than the spiral wound.
There's a lot more to it than I've provided here. You may want to post this to the piping and pressure vessel and/or boiler forum. I'm sure you'll get a lot more responses.
RE: Non-metal Gasket Seating Stress