Page 190 - Pipeline Rules of Thumb Handbook

Control Valves 177
Determine the Total Piping System Resistance:
Piping Component
or Feature
Entrance—Sharp Edged
1ft. of 3≤Sch. 40 Pipe
Fike 3≤ SRX-GI Rupture Disc
20ft. of 3≤Sch. 40 Pipe
3≤Sch. 40 Standard 90° Elbow
40ft. of 3≤Sch. 40 Pipe
Pipe exit—Sharp Edged
Total System Flow Resistance
The Darcy Equation defines the discharge of compressible actual DP/P¢ 1 to the limiting DP/P¢ 1 for sonic flow. Crane Table
fluids through valves, fittings and pipes. Since the flow rate A-22 shows limiting factors for k = 1.4 for sonic flow at a
into the example vessel is defined in SCFM, the following known value of K T . If (DP/P¢ 1 ) sonic < (DP/P¢ 1 ) actual , then the flow
form of the Darcy equation is used:
Flow Resistance Value
(K ) Reference
K 1 = 0.50 Crane 410Pg A-29
K 2 = 0.07 K = fL/D; f = .018 (Crane 410Pg A-26)
L = 1ft, ID = 3.068≤/12ft
K R = 0.99 National Board Cert. No. FIK-M80042
K 3 = 1.41 K = fL/D; f = .018 (Crane 410Pg A-26)
L = 20ft, ID = 3.068≤/12ft
K 4 = 0.54 Crane 410Pg A-29
K 5 = 2.82 K = fL/D; f = .018 (Crane 410Pg A-26)
L = 40ft, ID = 3.068≤/12ft
K 6 = 1.00 Crane 410Pg A-29
K T = 7.33 K T = K 1 + K 2 + K R + K 3 + K 4 + K 5 + K 6
Crane Equation 3-20
D PP
*¢ 1
¢= 678 * *d 2 SCFM
Y
q m
KT S g
1
q¢ m = rate of flow in cubic feet per minute at standard
conditions (14.7 psia and 60°F)
Y = net expansion factor for compressible flow through
orifices, nozzles and pipes (Crane 410Pg A-22)
d = internal diameter of pipe (in.)
DP = Change in pressure from state 1 to 2 (entrance to exit).
P¢ 1 = Pressure at state 1 (entrance) - psia
K = Loss coefficient
T 1 = Absolute temperature at state 1 (entrance) in degrees
Rankine (°R)
Sg = Specific gravity relative to air = 1.0 for this example
To determine Y, first it must be determined if the flow will
be sonic or subsonic. This is determined by comparing the
will be sonic.