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