Hi,

I have a problem by the calculation of flanges
I have a O-ring seating (m= 0 and Y = 0 according to table 2-5.1 of ASME section VIII div.1) but if I fill the value in a flange calculation of CAESAR II then I have a error "The specified gasket seating stress (y) is too low"
How can I solve the problem?

Kind regards
Koen

Design the O ring using non ASME methods Contact the O ring Manufatcturer
One excellent supplier of O ringss that I know of is Helicoflex.

Regarding self-energizing gaskets, Appendix 2 of VIII-Div1 has specific requirements within 2-5 BOLT LOADS,- (c) Required Bolt Loads- (3) Bolt loads for flanges using gaskets of the self-energizing type.

In 2-5 -(c)-3-(a) it is required: "Wm1 shall be sufficient to resist the hydrostatic end force H exerted by the maximum allowable working pressure on the area bounded by the outside diameter of the gasket."
This is a direct math consequence of the general formula
Wm1 = H + Hp
= 0.785G^2P + (2b X 3.14GmP)
with m=0

In 2-5 -(c)-3-(b)
Wm2 = 0
(I would add this is a consequence of y=0 in Wm2 = 3.14bGy)

It is very interesting the sentence following formula Wm2 = 0:
"Bolting, however, must be pretightened to provide a bolt load sufficient to withstand the hydrostatic end force H."
IMO, here ASME stipulate that it is required Wm2 = 0, but recognizes that Wm2 in seating must be at least "H" (which means also Wm1 for this type of gasket). It is the only place within ASME flange calculation where the gasket seating condition is linked with Operating condition ("P" generates "H"), and that sentence suggests that the required bolts load would be (at least) Wm1=Wm2=H.

Returning to your question about the impossibility to impose Wm2 = 0, my opinion is that a possible math solution to remain within ASME frame calculation would be to force an artificial "y" leading to Wm1=Wm2=H.
At least I think this approach is not in contradiction with the ASME sentence "Bolting, however, must be pretightened to provide a bolt load sufficient to withstand the hydrostatic end force H."
In the same time, I guess nobody shall be able to understand why "y" is a non-zero value, so about the practical utility of this approach/ calculation I prefer to have no more comments... please consider Mr. Luf suggestion!

Best regards.

I suggest you to read "ASME VIII-Div 1 Appx Y Flat face with metal-to-metal contact outside the bolt circle.

I suggest you to use this kind of flanges for the O-ring applications.

Kind regards,

Ibrahim Demir

If you proper specify the Facing Sketch (9- for O-ring), Caesar will ignore the value of Y that you insert in the Gasket Seating Stress=y field and will consider as 0.
Do some tests, insert any value you want, there will be no changes in results.



Regards,

Hi,

Thank you very much for all the response
I was also thinking what Mariog sayed but I was thinking for a low y but if Wm1=Wm2=H than I need a very huge value of y (481.25 MPa) where b = 1,5mm; G= 52.5mm; P= 55000KPa. If I putt the value in the calculation I have this result:
CALCULATED STRESSES (KPa )

OPERATING ALLOW SEATING ALLOW
--------- ----- ------- -----

Longitudinal Hub .. 148150 310000 126446 310000
Radial Flange ..... 204383 206667 174440 206667
Tangential Flange . 101358 206667 86509 206667
Maximum Average ... 176266 206667 150443 206667
Bolting ........... 265093 172375 183081 172375 *

and if I looking into flange.msg than I have strange values

-------------------- COMPUTATIONS FOR FLANGE @ NODE: 1 --------------------

NOTE: All values are printed in internal program units.
length : inches
force : pounds
stress : pounds per square inch
moments: inch-pounds

Ratios of 999.0, stress values of 0.0, and
MAWP values of .1E13 are not applicable to
the current flange.

EFFECTIVE GASKET WIDTH COMPUTATIONS:
CONTACT WIDTH OF GASKET, N = 0.1181
BASIC GASKET SEATING WIDTH, b0 = 0.059
EFFECTIVE GASKET SEATING WIDTH, b = 0.059
DIAMETER OF GASKET LOAD REACTION, G = 2.067

ORIGINAL DESIGN PRESSURE = 7977.258
AXIAL FORCE EQUIVALENT PRESSURE = 0.000
BENDING MOMENT EQUIVALENT PRESSURE = 3573.466
FINAL EQUIVALENT DESIGN PRESSURE = 11550.724

FLANGE AND BOLT LOAD CALCULATIONS :
HYDROSTATIC END FORCE AT G, H = 38757.0
GASKET COMPRESSION FORCE, HP = 0.0

OPERATING LOAD, Wm1 = 38757.0
GASKET SEATING LOAD, Wm2 = 26766.7
REQUIRED BOLT METAL AREA, Am = 1.550

TEMA BOLT INFORMATION:
TOTAL AREA, Ab = 1.01
MINIMUM SPACING = 1.250
REQUIRED RADIUS = 0.813
REQUIRED EDGE DISTANCE = 0.625

ACTUAL BOLT SPACING = 1.913
MAX ALLOWED SPACING = 13.000
CORRECTION FACTOR = 1.000

DIAMETER AND HUB PARAMETERS:
CORRODED FLANGE DIAMETER, B = 1.689
HUB DECAY LENGTH, H0 = 0.762
HUB RATIO, HL/H0 = 2.458
THICKNESS RATIO, G1/G0 = 2.355

MOMENT ARM RESULTS:
DISTANCE TO GASKET LOAD REACTION, hg = 1.467
DISTANCE TO FACE PRESSURE REACTION, ht = 1.561
DISTANCE TO END PRESSURE REACTION, hd = 1.250
DISTANCE TO FULL FACE ID GASKET, hg' = 0.000
DISTANCE TO FULL FACE OD GASKET, hg'' = 0.000

FLANGE FORCES:
HYDROSTATIC END FORCE AT B, HD, = 17872.7
PRESSURE FORCE ON FLANGE FACE, HT, = 20884.3

FLANGE DESIGN BOLT LOAD, W, = 31979.2
GASKET SEATING FORCE, HG, = 0.0

You can see that Wm1 is not = Wm2?
If I calculate Wm2 is it correct but Wm1 is not 0,785G^2P? Can someone explain this?

Other question I have with the calculation
How CAESAR II calculate "bending moment equivalent pressure" if I have a extrernally applied moment of 700 KPa. It is a 2" ASME 16.5 wn flange class 600lbs with a groove for the O-ring.
How CAESAR II calculate bolting stress? If I do bolt load (W)/(number of bolt (8bolts)*area of the bolt diameter 15.857 mm) than I don't get the value in the result.

It is not very importent because I need only the equivalent pressure for the CAESAR flexibility calculation but I want to know.

Kind regards
Koen

Dear Koen,

1. What I said is not a recommended procedure, it was just a suggestion to do something to pass a software limit as "The specified gasket seating stress (y) is too low".

But have you tried what DanB have written? It seems to be the right approach.

2. Obviously, you made a mistake in hand calculation when you've tried to impose "y" at that value.

3. I guess Wm1 is 0,785G^2P with p=FINAL EQUIVALENT DESIGN PRESSURE = 11550.724

4. "How CAESAR II calculate "bending moment equivalent pressure" if I have a externally applied moment of 700 KPa?"
I think it's M=700 Nm and
BENDING MOMENT EQUIVALENT PRESSURE= 16*M/PI/G^3
and
FINAL EQUIVALENT DESIGN PRESSURE=
=ORIGINAL DESIGN PRESSURE+
+BENDING MOMENT EQUIVALENT PRESSURE

5.About bolt selection, please see ASME VIII, Div1

best regards.

Hi Mariog,

Thank you for your reponse
I know it is a possible explanation but if I read the code of the bolt loads careful than I understand your way of thinking.

I have tried what DanB said even before I have open this topic but I have the similar error if I fill zero in the field of y.
If I have do it with colomn II so b is zero so Wm2 is zero and then I can change y without change the result but zero or a little value of y is impossible. Even with colomn I

If I calculate with the maximum value of pressure then is Wm1=Wm2=H
thank you

And for the bolt selection, I have make a little mistake with typing of the bolt diameter so that CAESAR take a lower bolt area from Tema than it have to do.

best regards