Flat face flanges with metal-to-metal contact outside the bolt circle for class 1 flange assembly (identical flange pairs)

Flange dimensions D t h g 0 g 1 B G C A R r
Flange dimensions
Flange forces h T h G H T H G H C h C h Cmax W P P M H Q Q H D H D h D
Flange forces
(a) Integral Illustrated t t B B
(a) Integral Illustrated
(b) Integral with Spacer t t B B t s
(b) Integral with Spacer
(c) Loose-Type with Hub t t B B
(c) Loose-Type with Hub

Values for calculation

$T$ $\mathrm{°C}$
$S_f$ $\mathrm{MPa}$
$S_n$ $\mathrm{MPa}$
$S_b$ $\mathrm{MPa}$
$P$ $\mathrm{MPa}$
$A$ $\mathrm{mm}$
$B$ $\mathrm{mm}$
$C$ $\mathrm{mm}$
$d_b$ $\mathrm{mm}$
$D$ $\mathrm{mm}$
$G$ $\mathrm{mm}$
$h_C$ $\mathrm{mm}$
$t$ $\mathrm{mm}$
$g_0$ $\mathrm{mm}$
$g_1$ $\mathrm{mm}$
$h$ $\mathrm{mm}$
$A_b$ $\mathrm{mm^2}$
$H_G$ $\mathrm{N}$
$t_s$ $\mathrm{mm}$


Factor $ h_0 $

$$h_0=\sqrt{B\cdot g_0}$$

Factor $ A $


Factor $ C $


Factor $ C_1 $


Factor $ C_2 $

$$C_2=5/42+17\cdot A/336$$

Factor $ C_3 $


Factor $ C_4 $

$$C_4=11/360+59\cdot A/5040+\left(1+3\cdot A\right)/C$$

Factor $ C_5 $

$$C_5=1/90+5\cdot A/1008-\left(1+A\right)^3/C$$

Factor $ C_6 $

$$C_6=1/120+17\cdot A/5040 +1/C$$

Factor $ C_7 $

$$C_7=215/2772+51\cdot A/1232+\left(60/7+225\cdot A/14+75\cdot A^2/7+5\cdot A^3/2\right)/C$$

Factor $ C_8 $

$$C_8=31/6930+128\cdot A/45045+\left(6/7+15\cdot A/7+12\cdot A^2/7+5\cdot A^3/11\right)/C$$

Factor $ C_9 $

$$C_9=533/30240+653\cdot A/73920+\left(1/2+33\cdot A/14+39\cdot A^2/28+25\cdot A^3/84\right)/C$$

Factor $ C_{10} $

$$C_{10}=29/3780+3\cdot A/704-\left(1/2+33\cdot A/14+81\cdot A^2/28+13\cdot A^3/12\right)/C$$

Factor $ C_{11} $

$$C_{11}=31/6048+1763\cdot A/665280+\left(1/2+6\cdot A/7+15\cdot A^2/28+5\cdot A^3/42\right)/C$$

Factor $ C_{12} $

$$C_{12}=1/2925+71\cdot A/300300+\left(8/35+18\cdot A/35+156\cdot A^2/385+6\cdot A^3/55\right)/C$$

Factor $ C_{13} $

$$C_{13}=761/831600+937\cdot A/1663200+\left(1/35+6\cdot A/35+11\cdot A^2/70+3\cdot A^3/70\right)/C$$

Factor $ C_{14} $

$$C_{14}=197/415800+103\cdot A/332640-\left(1/35+6\cdot A/35+17\cdot A^2/70+A^3/10\right)/C$$

Factor $ C_{15} $

$$C_{15}=233/831600+97\cdot A/554400+\left(1/35+3\cdot A/35+A^2/14+2\cdot A^3/105\right)/C$$

Factor $ C_{16} $

$$C_{16}=C_1\cdot C_7\cdot C_{12}+C_2\cdot C_8\cdot C_3+C_3\cdot C_8\cdot C_2-\left(C_3^2\cdot C_7+C_8^2\cdot C_1+C_2^2\cdot C_{12}\right)$$

Factor $ C_{17} $

$$C_{17}=\left[C_4\cdot C_7\cdot C_{12}+C_2\cdot C_8\cdot C_{13}+C_3\cdot C_8\cdot C_9-\left(C_{13}\cdot C_7\cdot C_3+C_8^2\cdot C_4+C_{12}\cdot C_2\cdot C_9\right)\right]/C_{16}$$

Factor $ C_{18} $

$$C_{18}=\left[C_5\cdot C_7\cdot C_{12}+C_2\cdot C_8\cdot C_{14}+C_3\cdot C_8\cdot C_{10}-\left(C_{14}\cdot C_7\cdot C_3+C_8^2\cdot C_5+C_{12}\cdot C_2\cdot C_{10}\right)\right]/C_{16}$$

Factor $ C_{19} $

$$C_{19}=\left[C_6\cdot C_7\cdot C_{12}+C_2\cdot C_8\cdot C_{15}+C_3\cdot C_8\cdot C_{11}-\left(C_{15}\cdot C_7\cdot C_3+C_8^2\cdot C_6+C_{12}\cdot C_2\cdot C_{11}\right)\right]/C_{16}$$

Factor $ C_{20} $

$$C_{20}=\left[C_1\cdot C_9\cdot C_{12}+C_4\cdot C_8\cdot C_3+C_3\cdot C_{13}\cdot C_2-\left(C_3^2\cdot C_9+C_{13}\cdot C_8\cdot C_1+C_{12}\cdot C_4\cdot C_2\right)\right]/C_{16}$$

Factor $ C_{21} $

$$C_{21}=\left[C_1\cdot C_{10}\cdot C_{12}+C_5\cdot C_8\cdot C_3+C_3\cdot C_{14}\cdot C_2-\left(C_3^2\cdot C_{10}+C_{14}\cdot C_8\cdot C_1+C_{12}\cdot C_5\cdot C_2\right)\right]/C_{16}$$

Factor $ C_{22} $

$$C_{22}=\left[C_1\cdot C_{11}\cdot C_{12}+C_6\cdot C_8\cdot C_3+C_3\cdot C_{15}\cdot C_2-\left(C_3^2\cdot C_{11}+C_{15}\cdot C_8\cdot C_1+C_{12}\cdot C_6\cdot C_2\right)\right]/C_{16}$$

Factor $ C_{23} $

$$C_{23}=\left[C_1\cdot C_7\cdot C_{13}+C_2\cdot C_9\cdot C_3+C_4\cdot C_8\cdot C_2-\left(C_3\cdot C_7\cdot C_4+C_8\cdot C_9\cdot C_1+C_2^2\cdot C_{13}\right)\right]/C_{16}$$

Factor $ C_{24} $

$$C_{24}=\left[C_1\cdot C_7\cdot C_{14}+C_2\cdot C_{10}\cdot C_3+C_5\cdot C_8\cdot C_2-\left(C_3\cdot C_7\cdot C_5+C_8\cdot C_{10}\cdot C_1+C_2^2\cdot C_{14}\right)\right]/C_{16}$$

Factor $ C_{25} $

$$C_{25}=\left[C_1\cdot C_7\cdot C_{15}+C_2\cdot C_{11}\cdot C_3+C_6\cdot C_8\cdot C_2-\left(C_3\cdot C_7\cdot C_6+C_8\cdot C_{11}\cdot C_1+C_2^2\cdot C_{15}\right)\right]/C_{16}$$

Factor $ C_{26} $


Factor $ C_{27} $

$$C_{27}=C_{20}-C_{17}-5/12+C_{17}\cdot C_{26}$$

Factor $ C_{28} $

$$C_{28}=C_{22}-C_{19}-1/12+C_{19}\cdot C_{26}$$

Factor $ C_{29} $


Factor $ C_{30} $


Factor $ C_{31} $

$$C_{31}=3\cdot A/2-C_{17}\cdot C_{30}$$

Factor $ C_{32} $

$$C_{32}=1/2-C_{19}\cdot C_{30}$$

Factor $ C_{33} $

$$C_{33}=0.5\cdot C_{26}\cdot C_{32}+C_{28}\cdot C_{31}\cdot C_{29}-\left(0.5\cdot C_{30}\cdot C_{28}+C_{32}\cdot C_{27}\cdot C_{29}\right)$$

Factor $ C_{34} $

$$C_{34}=1/12+C_{18}-C_{21}-C_{18}\cdot C_{26}$$

Factor $ C_{35} $


Factor $ C_{36} $

$$C_{36}=\left(C_{28}\cdot C_{35}\cdot C_{29}-C_{32}\cdot C_{34}\cdot C_{29}\right)/C_{33}$$

Factor $ C_{37} $

$$C_{37}=\left[0.5\cdot C_{26}\cdot C_{35}+C_{34}\cdot C_{31}\cdot C_{29}-\left(0.5\cdot C_{30}\cdot C_{34}+C_{35}\cdot C_{27}\cdot C_{29}\right)\right]/C_{33}$$

Factor $ E_1 $

$$E_1=C_{17}\cdot C_{36}+C_{18}+C_{19}\cdot C_{37}$$

Factor $ E_2 $

$$E_2=C_{20}\cdot C_{36}+C_{21}+C_{22}\cdot C_{37}$$

Factor $ E_3 $

$$E_3=C_{23}\cdot C_{36}+C_{24}+C_{25}\cdot C_{37}$$

Factor $ E_4 $

$$E_4=1/4+C_{37}/12+C_{36}/4-E_3/5-3\cdot E_2/2-E_1$$

Factor $ E_5 $

$$E_5=E_1\cdot\left(1/2+A/6\right)+E_2\cdot\left(1/4+11\cdot A/84\right)+E_3\cdot\left(1/70+A/105\right)$$

Factor $ E_6 $

$$E_6=E_5-C_{36}\cdot\left(7/120+A/36+3\cdot A/C\right)-1/40-A/72-C_{37}\cdot\left(1/60+A/120+1/C\right)$$

Factor $ F $ for integral type flanges


Factor $ F_L $ for loose type flanges

$$F_L=-\cfrac{C_{18}\cdot\left(\cfrac{1}{2}+\cfrac{A}{6}\right)+C_{21}\cdot\left(\cfrac{1}{4}+\cfrac{11\cdot A}{84}\right)+C_{24}\cdot\left(\cfrac{1}{70}+\cfrac{A}{105}\right)-\left(\cfrac{1}{40}+\cfrac{A}{72}\right)}{\left(\cfrac{C}{2.73}\right)^{\cfrac{1}{4}}\cdot\cfrac{\left(1+A\right)^3}{C}}$$

Factor $ V $ for integral type flanges


Factor $ V_L $ for loose type flanges

$$V_L=\cfrac{\cfrac{1}{4}-\cfrac{C_{24}}{5}-\cfrac{3\cdot C_{21}}{2}-C_{18}}{\left(\cfrac{2.73}{C}\right)^{\cfrac{1}{4}}\cdot\left(1+A\right)^3}$$

Factor $ F' $

- Category 1$$F'=g_0^2\cdot\left(h_0+F\cdot t\right)/V$$- Category 2$$F'=g_0^2\cdot\left(h_0+F_L\cdot t\right)/V_L$$- Category 3$$F'=0$$

Factor $ f $

if (Flange category = Category 1)$$f=C_{36}/\left(1+A\right)$$else$$f=1$$

Diameter $ B_1 $

if (Flange category = Category 3)$$B_1=B$$else if (Flange category = Category 1) ∧ $f \geq 1$$$B_1=B+g_0$$else$$B_1=B+g_1$$

Radial distance from bolt circle to point of intersection of hub and back of flange


Radial distance from the bolt circle, to the circle on which $ H_D $ acts

if (Flange category = Category 1)$$h_D=R+0.5\cdot g_1$$else$$h_D=\cfrac{C-B}{2}$$

Radial distance from bolt circle to outer edge of flange or spacer

$$h_{Cmax}=\cfrac{A-C}{2}$$$$h_C< h_{Cmax}$$

Shape factor for full face metal‐to‐metal contact flanges

$$β=\cfrac{C+B_1}{2\cdot B_1}$$

Shape factor

$$a=\cfrac{A+C}{2\cdot B_1}$$

Bolt hole aspect ratio used in calculating bolthole flexibility factor $ r_B $

$$\overline{AR}=\cfrac{n\cdot D}{π\cdot C}$$

Factor $ r_B $

$$r_B=\cfrac{1}{n}\cdot\left(\cfrac{4}{\sqrt{1-\overline{AR}^2}}\cdot\tan^{-1}\left(\sqrt{\cfrac{1+\overline{AR}}{1-\overline{AR}}}\right)-π-2\cdot \overline{AR}\right)$$

Factor $ J_S $

$$J_S=\cfrac{1}{B_1}\cdot\left[\cfrac{2\cdot h_D}{β}+\cfrac{h_C}{a}\right]+π\cdot r_B$$

Factor $ J_P $

$$J_P=\cfrac{1}{B_1}\cdot\left[\cfrac{h_D}{β}+\cfrac{h_C}{a}\right]+π\cdot r_B$$

Radial distance from gasket load reaction to the bolt circle


Radial distance from the bolt circle, to the circle on which $ H_T $ acts

if (Flange category = Category 1)$$h_T=\cfrac{R+g_1+h_G}{2}$$else$$h_T=\cfrac{h_D+h_G}{2}$$

Total hydrostatic end force

$$H=\cfrac{π}{4}\cdot G^2\cdot P$$

Hydrostatic end force on area inside of flange

$$H_D=\cfrac{π}{4}\cdot B^2\cdot P$$

Difference between total hydrostatic end force and the hydrostatic end force on area inside of flange


Moment due to $ H_D $ , $ H_T $ , $ H_G $

$$M_P=H_D\cdot h_D+H_T\cdot h_T+H_G\cdot h_G$$

Flange Moment Due to Flange‐Hub Interaction

$$M_S=-\cfrac{J_P\cdot F'\cdot M_P}{t^3+J_S\cdot F'}$$

Slope of Flange at Inside Diameter Times $ E $

$$Eθ_B=\cfrac{5.46}{π\cdot t^3}\cdot\left(J_S\cdot M_S+J_P\cdot M_P\right)$$

Contact force between flanges at $ h_C $


Bolt load at operating conditions


Operating bolt stress

$$σ_b=W_{m1}/A_b$$$$σ_b\le S_b$$

Strain length of bolt

$$l=2\cdot t+t_s+1/2\cdot d_b$$

Design prestress in bolts

$$S_i=σ_b-\cfrac{1.159\cdot h_C^2\cdot\left(M_P+M_S\right)}{a\cdot t^3\cdot l\cdot r_E\cdot B_1}$$

Radial flange stress at bolt circle

$$S_R=\cfrac{6\cdot\left(M_P+M_S\right)}{t^2\cdot\left(π\cdot C-n\cdot D\right)}$$$$S_R\le S_f$$

Radial flange stress at inside diameter

- Category 1$$S_R=-\left(\cfrac{2\cdot F\cdot t}{h_0+F\cdot t}+6\right)\cdot\cfrac{M_S}{π\cdot B_1\cdot t^2}$$- Category 2$$S_R=-\left(\cfrac{2\cdot F_L\cdot t}{h_0+F_L\cdot t}+6\right)\cdot\cfrac{M_S}{π\cdot B_1\cdot t^2}$$- Category 3$$S_R=0$$$$S_R\le S_f$$

Ratio of outside diameter of flange to inside diameter of flange


Factor $ Z $


Tangential flange stress at inside diameter

- Category 1$$S_T=\cfrac{t\cdot Eθ_B}{B_1}+\left(\cfrac{2\cdot F\cdot t\cdot Z}{h_0+F\cdot t}-1.8\right)\cdot\cfrac{M_S}{π\cdot B_1\cdot t^2}$$- Category 2$$S_T=\cfrac{t\cdot Eθ_B}{B_1}+\left(\cfrac{2\cdot F_L\cdot t\cdot Z}{h_0+F_L\cdot t}-1.8\right)\cdot\cfrac{M_S}{π\cdot B_1\cdot t^2}$$- Category 3$$S_T=\cfrac{t\cdot Eθ_B}{B_1}$$$$S_T\le S_f$$

Longitudinal hub stress

- Category 1$$S_H=\cfrac{h_0\cdot Eθ_B\cdot f}{0.91\cdot\left(g_1/g_0\right)^2\cdot B_1\cdot V}$$- Category 2$$S_H=\cfrac{h_0\cdot Eθ_B}{0.91\cdot\left(g_1/g_0\right)^2\cdot B_1\cdot V_L}$$- Category 3$$S_H=0$$if material of flange = Castings$$S_H\le S_f$$else$$S_H\le 1.5\cdot S_f$$if material of nozzle neck, vessel or pipe wall = Castings$$S_H\le S_n$$else$$S_H\le 1.5\cdot S_n$$


$$\left(S_H+S_R\right)/2 \le S_f$$$$\left(S_H+S_T\right)/2 \le S_f$$