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Sealing Flanges with Gaskets Bolt Torque Requirements Calculator

Hydraulic & Pneumatic Design Engineering
Pressure Vessel Pipes Design Engineering ASME

Bolt Torque Required for Sealing Flanges with Gaskets and Internal Pressure

Preview Bolt Torque Required for Sealing Flanges with Gaskets Calculator (Premium Membership required for calculator)

 

Equivalent Pressure
Eq. 1

${\displaystyle P_c=\frac{16M}{\mathrm{\pi <!--\; \pi \; -->}{G}^3}+\frac{4P_r}{\mathrm{\pi <!--\; \pi \; -->}{G}^2}+P}$

Hydrostatic end force, H, lb
Eq. 2

${\displaystyle H=\frac{\mathrm{\pi <!--\; \pi \; -->}{G}^2{P}_c}{4}}$

Total joint-contact-surface compression load, H_p, lb
Eq. 3

${\displaystyle H_p=2\cdot <!--\; \cdot \; -->b\cdot <!--\; \cdot \; -->\mathrm{\pi <!--\; \pi \; -->}\cdot <!--\; \cdot \; -->G\cdot <!--\; \cdot \; -->m\cdot <!--\; \cdot \; -->P_c}$

Minimum required bolt load for gasket seating, W_m2, lb.
Eq. 4

${\displaystyle W_{m2}=\mathrm{\pi <!--\; \pi \; -->}\cdot <!--\; \cdot \; -->b\cdot <!--\; \cdot \; -->G\cdot <!--\; \cdot \; -->y}$

Actual joint area contact for gasket, A_g, in²
Eq. 5

${\displaystyle A_g=2\cdot <!--\; \cdot \; -->\mathrm{\pi <!--\; \pi \; -->}\cdot <!--\; \cdot \; -->b\cdot <!--\; \cdot \; -->G}$

Decreasing compression force in gasket, ΔF, lb
Eq. 6

${\displaystyle \mathrm{\Delta <!--\; \Delta \; -->}F=\frac{H}{1+\frac{A_b{E}_b{t}_g}{A_g{E}_g{l}_b}}}$

Initial required tightening force (tension), F_bo, lb.
Eq. 7

${\displaystyle F_{bo}=H_p+\mathrm{\Delta <!--\; \Delta \; -->}F}$

Total tightening force required to seal joint, W, lb.
Eq. 8

W = greater of F_bo or W_m2

Required torque, T, ft-lb
Eq. 9

${\displaystyle T=\frac{K\cdot <!--\; \cdot \; -->W\cdot <!--\; \cdot \; -->d_m}{12\cdot <!--\; \cdot \; -->n}}$

Where:

P_e = equivalent pressure including external loads, psi
M = external bending moment, in.-lb
G = avaerage diameter at location of gasket load reaction, in.
P_r = radial load, lb
P = internal pressure, psi
b = effective gasket seating width (diameter), in.
m = gasket factor
W_m2 = required bolt load, gasket seating, lb
y = gasket unit seating load, psi
A_g = actual joint-contact area of gasket, in.²
ΔF = Decreasing compression force in gasket, lb
H = total hydrostatic end force, lb
A_b = cross-sectional area of bolts, in.²
E_b = modulus of elasticity of bolting material at temperature, psi
t_g = thickness of gasket, in.
l_b =
H_p = total joint-contact surface compression load, lb
F_bo = = initial tightening force, Ib
K = total friction factor between bolt / nut and nut / flange face
W = total tightening force, lb
d_m = pitch diameter of threads, in
n = number of bolts

Friction factor (typical)
Lubricated = 0.075-0.15
Nonlubricated = 0.15-0.25

Figure1 Flange and joint details.

Table 1, Torque Required in ft-lb to Produce the Following Bolt Stress

Bolt Size	15 ksi	30 ksi	45 ksi	60 ksi
1/2-13	15	30	45	60
5/8-11	30	60	90	120
3/4-10	50	100	150	200
7/8-9	80	160	240	320
1-8	123	245	368	490
1-1/8 - 8	195	390	533	710
1-1/4 - 8	273	500	750	1000
1-3/8 - 8	365	680	1020	1360
1-1/2 - 8	437	800	1200	1600
1-5/8 - 8	600	110	1650	2200
1-3/4 - 8	775	1500	2250	3000
1-7/8 - 8	1050	2000	3000	400
2-8	1125	2200	3300	4400
2-1/4 - 8	-	3180	4770	6360
2-1/2 = 8	-	4400	6600	8800
2-3/4 - 8	-	5920	8880	11840
3 - 8	-	7720	11580	15440

Notes:

1. Bolted joints in high-pressure systems require an initial preload to prevent the joint from leaking. The loads which tend to open the joint are:
a. Internal pressure.
b. Thermal bending moment.
c. Dead load bending moment.
2. Either stud tensioners or torque wrenches are used for prestressing bolts to the required stress for gasket seating. Stud tensioners are by far the most accurate. Stud tension achieved by torquing the nut is affected by many variables and may vary from 10% to 100% of calculated values. The following are the major variables affecting tension achieved by torquing:
a. Class of fit of nut and stud.
b. Burrs.
c. Lubrication.
d. Grit, chips, and dirt in threads of bolts or nuts.
e. Nicks.
f. The relative condition of the seating surface on the 3. Adequate lubrication should be used. Nonlubricated bolting has an efficiency of about 50% of a well-lubricated bolt. For standard applications, a heavy graphite and oil mixture works well. For high temperature service (500'F to 1000"F), a high temperature thread compound may be used.
4. The stiffness of the bolt is only 1/3 to 1/5 that of the joint. Thus, for an equal change in deformation, the change of the load in the bolt must be only 1/3 to 1/5 of the change in the load of the joint.
5. Joints almost always relax after they have first been tightened. Relaxation of 10% to 20% of the initial preload is not uncommon. Thus an additional preload of quantity F is required to compensate for this “relaxing” of the joint.

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Reference:

Pressure Design Manual, Third Edition, Dennis Moss 2004