Flat Faced Blind Flange

[blackhawk1109]

I am trying to determine the thickness of a flat faced blind flange with a dovetail grove machined in it for an o-ring. Similar to flanges in Appendix Y.
Now, if i go to Figure UG-34(k) this is the most similar flange to what i need however it is not flat faced. Would i just need to use equation (1) for this?


Flange Information:
Material: A36
O.D.: 37"
Bolt Circle:34 1/2"
Mean Diameter of O-ring: 30"

 

[HTURKAK]

ASME Section VIII Rules for Construction of Pressure Vessels =
'except when the head, cover, or blind flange is attached by bolts causing an edge moment [sketches (j) and (k)] in which case the thickness shall be calculated by..'

You are expected to use formula (2) which is,

t = d*SQRT ( CP/SE + 1.9Whg/SEd3)

 

[HTURKAK]

Dear blackhawk1109 (Mechanical)(OP),

I should draw back my first reply ..But I must add that you inclined me by choosing Figure UG-34 type (k) which is valid for RF blind.

In your case, ( which is FF blind) ,type p where C=0.25 applicable and equation (1) is valid.

Notice that , the preloading of the bolts for RF blind case , causing an edge moment [sketches (j)
and (k)] and increasing the blind thickness.

 

[david339933]

You should be using App. Y for both flanges, not UG-34. See Y-6.3(b).

 

[SnTMan]

blackhawk1109, see Y-5.1(c)

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[r6155]

blackhawk1109.
I feel that you are not in a right way.
Be careful with SA-36, depends of service.
You say that groove is in the blind flange. Are you sure?
Do you have experience during fabrication of flanges with O-Ring gasket?.

Regards

 

[blackhawk1109]

While I agree with what is being said I am still confused due to the difference is thicknesses that can be calculated. If I use UG-34 with Eq(1) you get 1.067 and Eq(2) 1.250 however with App.Y you get over 2". How is this possible?

If I were to use UG-34:
Equation (1):
t = d*sqrt(CP/SE)
d = 30" (Figure UG-34 (k) - mean oring diameter)
C = 0.30 (Figure UG-34 (k))
P = 70 psi
S = 16,600 psi (A36 @ Room Temp.)
E = 1 (No Welding)

t = 1.067"

Equation (2)
t = d*sqrt(CP/SE + 1.9Whg/SEd3)

W = Wm1
Wm1 = H + Hp = 0.785G2P + (2b x 3.14GmP)
G = 30"
m = 0 (Table 2-5.1 , O-rings)
W = Wm1 = 49,455 lb

hg = 2.25"

t = 1.250

If I were to use Appendix Y:
Y-9(b)
ta = 2.45 * sqrt(Mp/(pi*C-nD)Sf)
C = 34.5"
n = 28
D = 1.125"
Sf = 16,600 psi

Mp = HD*hD + HT*hT + HG*hG
HD = 0 (No inner diameter)
HG = 0 (Negligible)
HT = H - HD = 0.785*G2*P = 49,455lb
ht = 17.25"
Mp = 853,099 lb*in

ta= 2.00"
tb = 0 (B1 = 0)
tc = ta

Trial value for thickness is 1.1tc = 2.20"

 

[SnTMan]

Well I'd say different animals, different theories apply. BTW, at a glance I'm not sure I'd trust your Apx Y numbers...

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[r6155]

blackhawk1109
I confirm my feeling. I already imagined all this.
Sorry, but this is not for you. Contact a pressure vessel engineer.

Regards

 

[steeletc]

The difference between UG-34 and App Y is that in UG-3, the flanges are separated by a gasket (metal or flexible) on the inside of the bolt pattern such that prying action is eliminated and no extra load will develop in the bolts or the flanges than what would be apparent from seating and pressure. Appendix Y deals with flanges where the metal-to-metal contact of the flat faces induces the prying forces that can seriously increase the bending in the flanges and the bolts. App Y therefore will usually give thicker flanges.

The thing I become curious about is why the UG-34 equations and C values are slightly different than in Section III Div 1 NE; is this because Section VIII deals with higher pressure applications? I'd expect Section III to give as thick or thicker flanges.

Edit: I just realised that the difference appears to be a factor of 1.5 on both terms under the square root. Must be based on different allowable stresses.