Page 80 - Pressure Vessel Design Manual

General Design 61

Modulus of Elasticity of Gasket Material, E, Required torque, T, ft-lh.

Ring joint and flat metal: Select values from ASME
Section 11, or Appendix K of this book.
Comp asb = 70 ksi
Rubber = 10 ksi Notes
Grafoil = 35 ksi
Teflon = 24 ksi 1. Bolted joints in high-pressure systems require an initial
Spiral wound = 569 ksi preload to prevent the joint from leaking. The loads
which tend to open the joint are:
a. Internal pressure.
Friction Factor, K b. Thermal bending moment.
c. Dead load bending moment.
Lubricated = 0.075-0.15 2. Either stud tensioners or torque wrenches are used for
Nonlubricated = 0.15-0.25 prestressing bolts to the required stress for gasket seat-
ing. Stud tensioners are by far the most accurate. Stud
tension achieved by torquing the nut is affected by
Calculations many variables and may vary from 10% to 100% of
calculated values. The following are the major variables
Equicalent pressure, P,, psi affecting tension achieved by torquing:
a. Class of fit of nut and stud.
16M 4P,
P,=-+-+P b. Burrs.
nC3 nC2 c. Lubrication.
d. Grit, chips, and dirt in threads of bolts or nuts.
e Hydrostatic end force, H, lh e. Nicks.
f. The relative condition of the seating surface on the
flange against which the nut is rotated.
3. Adequate lubrication should be used. Nonlubricated
bolting has an efficiency of about 50% of a well-lubri-
e Totaljoint-contact-surface compression load, H,,, lh. cated bolt. For standard applications, a heavy graphite
and oil mixture works well. For high temperature ser-
Hp = BbnGmP, vice (500'F to 1000"F), a high temperature thread
compound may be used.
Minimum required bolt load for gasket seating, WTnz, lb.
Table 2-8
W,,,2 = nbCv Bolt Torques
Torque Required in R-lb to Produce the Following Bolt Stress
e Actualjoint area contact for gasket, A,,
Bolt Size 15ksi 30 ksi 45 ksi 60 ksi
A, = 2nbG -13 15 30 45 60
%-11 30 60 90 120
Decreasing compression force in gasket, AF, lb % -10 50 100 150 200
7* -9 80 160 240 320
1-8 123 245 368 490
1% -8 195 390 533 71 0
1% -8 273 500 750 1000
1% -8 365 680 1020 1360
1% -8 437 800 1200 1600
e Initial required tightening force (tension), Fbo, lb. 1% -8 600 1100 1650 2200
1% -8 775 1500 2250 3000
1% -8 1050 2000 3000 4000
Fb<, = HI, + AF 2-8 1125 2200 3300 4400
2% -8 - 31 80 4770 6360
Total tightening force required to seal joint, W, lh. 2% -8 - 4400 6600 8800
2% -8 - 5920 8880 1 1840
W = greater of Fhl, or W,,,2 3-8 - 7720 1 1580 15440