Flange design per ASME VIII Div 1 Appendix 2

[SMiK21]

Hi all,

I'm trying to calculate a loose flange (sketch 3a of fig 2-4) that will be fabricated. I've started out with the dimensions of a DIN 2575 flange (same as EN 1092 Type 1). I'm going to use a Klingersil C-4324 gasket.

Now, my problem is that the stresses I get are nowhere near the allowable - as high as 2.64 times the allowable stress for operating conditions and 6.4 times the allowable stress for gasket seating. My working pressure is half of the flange's rated pressure, temperature is room temperature.

I think I have understood the principles correctly:
Wm1 is the bolt preload needed to resist the hydrostatic end force
Wm2 is the bolt preload needed for gasket seating - Wm2 governs over Wm1, which makes sense.

I then need to calculate 2 different W (bolt forces): one for operating conditions, which is the same as Wm1, and another for gasket seating, which takes into account the possibility of overbolting. These forces will be used to calculate the flange stress.

This is were things get trickier: both of these W are too high, specially taking into account that the working pressure is half of the rated pressure and that I am using the standard number of bolts for this dimension of flange!

Any thoughts? Am I using the wrong gasket? Apparently not, if I change the gasket parameters the results don't alter significantly... I can't reduce the bolting because it will be connected to a valve that comes with a standard flange.

Data, in case anyone is interest in crunching the numbers (SI units):
Flange standard: DIN 2575, DN 1600, PN6 (44 mm thickness)
Material: S235
Working pressure: 3 bar
Bolts: 40 x M33, 8.8 Class
Gasket: Klingersil C-4324 OD 1720 mm/ID 1620 mm, t = 2mm, m = 3.5, y = 20 N/mm2

 

[TGS4]

What happens when you use the rated pressure as the working pressure?

 

[prex]

The thickness of the flange is not suitable for a standard gasket laying inside the bolt holes. You could use a full face gasket and calculate accordingly.

prex
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[SMiK21]

What happens when you use the rated pressure as the working pressure?

Admissable stress: 103 N/mm2

P = 3 bar, working stress = 272 N/mm2
P = 6 bar, working stress = 525 N/mm2

The thickness of the flange is not suitable for a standard gasket laying inside the bolt holes. You could use a full face gasket and calculate accordingly.

44 mm isn't enough? Although that's what the spreadsheet tells me, I don't find it intuitive. According to my calculations, only a 112 mm thickness flange would be enough to check the stress due to bolting. This doesn't seem right at all.

If I were to use a full face gasket, I think that I should treat it as a flange with metal-to-metal contact outside the bol circle and use Appendix Y to calculate it, right?

 

[prex]

App.Y does not account for a soft gasket, it assumes metal to metal contact. EN13445 has a method for the type of joint: you can see a calculation sheet here.

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[SMiK21]

With EN 13445 11.6 I get 66 mm, also too high.

 

[prex]

The thickness of a full face soft gasket flange strongly depends on the softness of the gasket. Try with a rubber gasket and you'll see.
If you give me your flange dimensions I can run a calculation. However I wonder how you determine the allowable stresses for 8.8 and S235 materials, as, I may be in error, but they shouldn't be listed for pressure vessel applications.

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