Non-metal Gasket Seating Stress 1

[mylexicon]

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

 

[pipesvessels1]

drno,

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

 

[sjrfc2]

The tanged graphite is a flexible graphite sheet laminated on a tanged (spiky) reinforcement sheet of 316 stainless (not the spiral wound). Garlock makes one brand of this (Garlock Graph-Lock 3125TC). The Garlock literature calls out a y value of 2500 psi for the 1/16" thick sheet and 3000 psi for the 1/8" sheet. The M values are 2.6 and 6.0 for the 1/16" and 1/8" respectively.

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.

 

[mylexicon]

Doesn't the Spiral Wound gasket fall into the metallic gasket category? The gasket I was refering to is specified as non-metallic in the Pipe Material Spec.
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

 

[sjrfc2]

The graphite did replace the asbestos in the spiral wound applications but this tanged graphite gasket is different. It is a sheet gasket. It can be cut to fit standard flanges or irregular shapes. The center is a thin stainless sheet that is spiky (like a cheese grater). On each side of the stainless sheet is laminated graphite. The spiky center sheet helps prevent extrusion. The graphite sheet is soft and easily compressed. Spiral wound gaskets take a lot more to bolt load to compress.

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.

 

[mylexicon]

Thanks alot 'sjrfc2'. Now I have a picture of what this thing (tanged graphite gasket) looks like. What you provided was enough for me. I'll see if I can get a hold of manufacturer's catalogues for these products.