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388-Two Ways to Calculate the Equivalent Pressure for Piping Flanges
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Two ways to calculate the equivalent pressure for piping flanges, based on the 2007 ASME VIII Div2 relations
Note: the meaning of the symbols are described in 2007 ASME VIII Div2
The 2007 ASME VIII Div 2 design flange model is based on the conservative assumption that the pressure and the external loads are changing the
gasket load while the bolts load remains at constant value 0W . Maintaining the same conservative assumption, this model can be adapted for the
piping flange checking case.
D
EAeq
hC
MFF
2
F4 M
−+=
where
MF is the factor II.
IF
PM
+=
38460
2
4GH*
π= ,
2
4BH*D
π= and [ ]22
4BGH*T −
π=
Based on this model, the external loads alone, AF and EM , can be converted into equivalent pressure.
The equivalence may be made in two ways and gives complementary results.
The first pressure equivalence may be considered in terms of pressure that gives the same gasket load as that one given by the external
loads. This is the gasket load equivalence.
That means:
eqe* FWpHW −=− 00
DP
EA
D
EMA
D
EMA**
eqe
hC
G
II.
I
G
M
G
F
)hC(G
MF
G
F
hC
MFF
HH
Fp
238460
164
2
164
2
413222 −+π
+π
=−π
+π
=
−+==
It is worth to note the similitude with the Kellogg/ASME III Code formulas.
Under the operational conditions (i.e. p , AF and EM as flange’s loads), the gasket load must remain greater than the gasket load at the rating
pressure, as a gasket tightness reserve. This condition is covered by imposing the limit RATINGe ppp <+ .
The second pressure equivalence may be considered in terms of pressure that gives the same bending moment as that one given by the
external loads. This is bending moment/ flange stress/ J index equivalence.
The equivalence condition is:
( ) Te*TDe
*DGe
*DeqGeq hpHhpHh)pHW(hFhFW ++−=+− 00
( )( )
[ ]
( )
GTD
GDPD
EA
GTD
GDD
MEA
G*
T*TD
*D
GDeqe
hGh)BG(hB
hhII.
I
hC
MF
hGhBGhB
hhhC
FMF
hHhHhH
hhFp
22222222
384602
4
4
444
2
4
−−+
−
+−+
π=
π−−
π+
π
−
−+
=−+
−=
This is the bending moment equivalence and the total pressure epp + can be introduced as pressure for the calculation of the ASME VIII flange
stress and ASME VIII J index. The total pressure calculated in this way shouldn’t be limited to the RATINGp , unless there is the real intention to
limit the flange stress and the J index to the values corresponding to the pressure rating. Instead, the ASME VIII Div2 limits must be considered
for the flange stress and J index.
the ASME VIII Div 2/ KOVES model
F
M
A
E
eqF
Dh
C
C-2hD
*H (p)= H pD D
internal pressure p
GH (p, F )=W -H p - F
hG
0
*
0W
TTH (p)= H p*
eq
Th
eq
must remain greater than 2πbGmp
RATING
B
G
hD
FeqW
Gh
W -Feq
0
0 GH (p)=W -H p
hG
Dh
0
*
0W
*H (p)= H pD D
TTH (p)= H p*
e
e
e
Th
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