(1) for the globe valve - 16 feet, (2) for the standard elbow - 2 feet, and

(3) for the angle valve - 8 feet. With a pipe length of 120 feet, the total

equivalent pipe length is 146 feet. This gives a total estimated pressure

drop of 312 psi. Since this is less than the estimated 570 psi (1420 psia

-850 psia), a lower inlet pressure can be used.

With the size of the pipe known and the pressure conditions approximated, it

is now possible to obtain a closer approximation by using Equation (1). If

an inlet pressure of 1250 psia is used, giving an effective system pressure

of 1050 psia P1 + P2, the following values for Equation (1) can be

calculated:

-----------

2

(0.01 - see Table 5-5)

p

[rho] = 0.71 lb/ft3 from ---------------------- = ----

14.7

1050

f = 0.026 (see Figure 5-1 for 3/4-inch, Schedule

160 pipe, turbulent flow)

L = 146 ft (see above)

V = 252 ft/sec.

(a)

Calculate compressed flow from Equation (3):

14.7

V2

---- = ----

and V2 = 31.1 ft 3 or

1050

2220

Q = 31.1 ft3/min.

(b)

Next calculate flow velocity:

Q

31.1

V = - or ------------------------

A

0.00206 (see Table 5-11)

V = 15,100 ft/min or 252 ft/sec

D = 0.512 ft (see Table 5-11

then using equation (1):

0.71 x 0.026 x 146 x 2522

[DELTA]P = ---------------------------

144 x 0.512 x 2 x 32.2

[DELTA]P = 360 psi

Since this is close to the permissible pressure drop of 400 psi, it can be

estimated that the inlet pressure can be close to 1250 psi.

3.

DESIGN FOR PRESSURE. The design of a piping system for pressure

capability requires that a design pressure P and a design temperature T be

established for the piping system. The design pressure must not be less than

the maximum difference in pressure across the pressure boundary for any

normal operating condition. The design temperature must not be less than the

actual metal temperature which exists for any specified normal operating

condition.

Integrated Publishing, Inc. |