Page 199 - Pressure Vessel Design Manual

Design of Vessel Supports 177

Notes and the wear plate extends W10 (5.73 deg.) above the
horn of the saddle.
1. Horizontal vessels act as beams with the following 7. If it is determined that stiffening rings will be required
exceptions: to reduce shell stresses, move saddles away from the
a. Loading conditions vary for full or partially full ves- heads (preferable to A=0.2 L). This will prevent
sels. designing a vessel with a flexible center and rigid
b. Stresses vary according to angle 8 and distance “A.” ends. Stiffening ring sizes may be reduced by using a
c. Load due to weight is combined with other loads. saddle angle of 150”.
2. Large-diameter, thin-walled vessels are best supported 8. An internal stiffening ring is the most desirable from a
near the heads, provided the shell can take the load strength standpoint because the maximum stress in the
between the saddles. The resulting stresses in the shell is compressive, which is reduced by internal pres-
heads must be checked to ensure the heads are stiff sure, An internal ring may not be practical from a pro-
enough to transfer the load back to the saddles. cess or corrosion standpoint, however.
3. Thick-walled vessels are best supported where the 9. Friction factors:
longitudinal bending stresses at the saddles are about
equal to the longitudinal bending at midspan.
However, “A” should not exceed 0.2 L. Friction
4. Minimum saddle angle 8= 120”, except for small ves- Surfaces Factor, p
sels. For vessels designed for external pressure only 8 Lubricated steel-to-concrete 0.45
should always = 120”. The maximum angle is 168” if a Steel-to-steel 0.4
wear plate is used. Lubrite-to-steel
5. Except for large L/R ratios or A > W2, the governing 0 Temperature over 500°F 0.15
stress is circumferential bending at the horn of the 0 Temperature 500°F or less 0.10
saddle. Weld seams should be avoided at the horn of 0 Bearing pressure less than SOOpsi 0.15
the saddle. Teflon-to-Teflon
6, A wear plate may be used to reduce stresses at the horn 0 Bearing 8OOpsi or more 0.06
of the saddle only if saddles are near heads (A 5 W2), 0 Bearing 3OOpsi or less 0.1

PROCEDURE 3-11

DESIGN OF SADDLE SUPPORTS FOR LARGE VESSELS [4, 15-17, 211

F, =allowable axial stress, psi (see App. L)
Notation N = number of anchor bolts in the fEed saddle
a, = cross-sectional area of bolts in tension, in. 2
A, = cross-sectional area of saddle, im2 Y =effective bearing length, in.
Ab =area of base plate, T =tension load in outer bolt, Ib
AI.= projected area for wind, ft2 nl = modular ratio, steel to concrete, use 10
AD =pressure area on ribs, in. 2 Fb = allowable bending stress, psi
A, = cross-sectional area, rib, in. 2 Fy =yield stress, psi
Q = maximum load per saddle, lb fh = saddle splitting force, lb
Qi = Qo + QH, lb fa = axial stress, psi
Q2 = Qo + QL, lb fb =bending stress, psi
Qo = load per saddle, operating, lb f,, = unit force, lb/in.
QT = load per saddle, test, lb B, =bearing pressure, psi
QL =vertical load per saddle due to longitudinal loads, lb M =bending moment, or overturning moment, in.-lb
QR =vertical load per saddle due to transverse loads, lb I = moment of inertia, in. 4
FL. = maximum longitudinal force due to wind, seismic, Z = section modulus, in.3
pier deflection, etc. (see procedure 3-10 for r =radius of gyration, in.
detailed description) K1 = saddle splitting coefficient