Page 60 - Pipeline Rules of Thumb Handbook

Construction 47

E = 29 10 6 lb sq in. Minimum Radius of Curvature, R
¥
Yield Stress
,
I = 1 943 in. 4
(psi) F = 0.72 F = 0.6 F = 0.5 F = 0.4
Z = 162 in. 3 35,000 863D 1,036D 1,243D 1,553D
42,000 719D 863D 1,036D 1,295D
S A = 25 500 psi (from Code for Pressure Piping ) 46,000 657D 788D 946D 1,182D
,
52,000 581D 697D 836D 1,046D
,
3 ¥ 29 10 6 ¥ 1 943 56,000 539D 647D 777D 971D
¥
R = = 20 460 in or 1 705 ft. 60,000 503D 604D 725D 906D
.
,
,
,
2 ¥ 162 ¥ 25 500 65,000 465D 558D 669D 836D
70,000 431D 518D 621D 776D
The section modulus = Z = 2I/D, and may be simplified to
80,000 377D 453D 544D 680D
Z = I/r and substituted for Z in Equation 12.
I = Moment of inertia
r = Distance from center pipe
D = Outside diameter of pipe
Example. What is the minimum radius of curvature that
Equation 12 then becomes: can be used without overstressing 42≤ API 5LX X-65 line pipe
at 72°F used in type C construction (gas line)? The design
2
R = 3 Er Sa (13) factor from ANSI B31.8 is 0.5; therefore use the column
headed F = 0.5.
¥
.
R = (21 75 10 6 Sa) ¥ D (14)

,
,
R = 669 ¥ 42 ¢¢ = 28 098 ¢¢ or 2 342 ft
Sa, the allowable stress, is determined by the design factor
permitted by the design code used. Equation 14 may be For liquid lines designed in accordance with ANSI B31.4, use
further simplified by using the following table. the column headed F = 0.72.
Determine length of a pipe bend

For smooth bends (other than wrinkle bends) use the fol- Example. Find the length of a piece of pipe required to
lowing formula: make a 90° bend with a radius of 60in. There’s to be a four-
in. tangent at either end.
L = ?
¥
L = R D ¥ .017 + T R = 60
D = 90
where L = length of bend T = 8
R = radius of bend (center line of pipe) L = 60 ¥ 90 ¥ .01745 + 8
D = number of degrees in the bend = 94.23 + 8
T = total length of the two tangents at either end = 102.23in.

Length of pipe in arc subtended by any angle

Application angle of 42∞ subtends an arc = 0 7330¢¢
.
.
angle of 35¢ subtends an arc = 0 01018¢¢
To find the length of pipe subtended by an angle of 42° -
.
35 feet with a radius of 24 inches. 0 7432¢¢
Assuming R = 1 inch,