What are the factors needed to calculate steam &
water pipe line sizes?
Quantity of maximum & minimum flow through the line
Pressure & temperature of the fluid
Pressure drop allowed
Velocity of the fluid in pipe
Density & specific volume of the fluid
How do you measure the steam flow through the pipe?
Steam flow is measured with the help of orifice plate, flow
nozzles etc
How do you measure the water flow through the pipe?
Water flow is measured with the help of orifice plate,
vortex meter, Rota meter & turbine meters installed in pipe lines.
What is the importance for calculating pipe line size for
particular fluid flow?
To provide correct required flow
To avoid pressure drop of fluid
To avoid starvation
Why the velocity is the important factor while
calculating the line size?
Flow = Area of the pipe X Velocity
By looking at the above relation, velocity is the critical
& important parameters, as miss judgment of velocity may lead to wrong
result.
Fluid having high pressure will be having high velocity &
hence require lesser pipe line size & vice versa
And also fluid having lower density will be having high
velocity & hence lesser pipe size and vice versa
What are the assumed velocity for various fluids flow?
Velocity of water at the suction of pump = 0.7 to 0.9 m/sec
Feed water flow at pressure 87 kg/cm2 = 2 to 4 m/sec
Saturated steam = 25 to 50 m/sec
Superheated steam = 30 to 70 m/sec
What will happen if a 6” pipe line carrying hot water at
the rate of 100 TPH suddenly contracts to 4”?
Following shall be observed
Velocity in the pipe will increase suddenly
Head or pressure loss will occur
Energy required to pump the water will increase
What are the factors that can cause the pressure drop in
a pipe line?
Friction factor of pipe (pipe internal wall roughness)
Length of the pipe
Diameter of the pipe (size of the pipe)
Velocity of fluid in the pipe line
Pipe line fittings like valves, bend, tee etc. present in
the pipe line
What are the effects of over sizing the pipe lines?
The cost of pipe lines & related fittings like valves,
bend, Tee etc. will increase accordingly
Higher installation cost including pipe line supports &
insulations
For higher sized steam pipe lines more condensate will tend
to form & hence more number of steam traps are required
For higher sized steam pipe lines, there is more possibility
of carryover wet steam to end user
More heat loss due to more exposed heat/hot surface area
What are the effects of under sizing the pipe lines?
For under sized pipe lines low pressure will be available
for end user
In steam lines more pressure drop may cause starvation in
pipe lines
Chance of erosion
Chance of water hammer & noise
Calculations:
1. Calculate the pipe line size required to pump 100
m3/hr of water at pressure 85 kgg/cm2 to the Boiler.
As discussed in the above theory part, velocity of the feed
water at pressure 85 kg/cm2 is around 3 m/sec
Then flow, Q = Area of pipe line in M2 X Velocity in meter
(100/3600) m3/sec = (3.142 X D^{2}/4) X 3 m/sec
D = 0.108 m = 108 mm
Looking at the above value, the pipe line size required
should have internal diameter 108mm.
Then pipe line size = Pipe ID + 2 X thickness
For feed water pipe line having above pressure needs minimum
80 schedule, so refer carbon steel pipe line chart & select the required
schedule & thickness.
2. Calculate the main steam pipe line size
required for connecting Boiler out let steam to distribution header. Maximum steam
flow is 125 TPH at pressure 110 kg/cm2 & temperature 540 deg C, assume
velocity of steam in pipe line is 52 m/sec
Steam flow = 125 TPH = 125000 kg/hr
Density of steam at pressure 110 kg/cm2 & 540 deg C = 32
kg/m3...Refer steam table
Steam flow in m3/sec = 1250000 / (32 X 3600) = 1.08 m3/sec
We have,
Q = AV
1.08 = A X 52
A = 0.02 M2
A = 3.142 X D^{2}/4
0.02 = 3.142 X D^{2}/4
D = 0.159mm = 160 mm
So need pipe line of internal diameter 150 mm
Note: Outer diameter of the pipe line is standard, need to
select schedule based on operating pressure & temperature to get desired
line size.
3Calculate the velocity of 55 TPH saturated steam
flowing in 500 NB pipe line at pressure 1.7 kg/cm2 & 135 deg C
Density of steam at pressure 1.7kg/cm2 & temperature =
1.5 kg/m3
Steam flow in m3/sec = 55 X 1000 / (1.5 X 3600) = 10.18
m3/sec
We have,
Q = AV
10.18 = (3.142 X 0.9^{2}/4) X V
V = 15.99 m/sec
Following are the various cases taken as case study for pipe
line size
Case1
Pressure (kg/cm2)

2.7

Temperature (deg c)

135

Density (kg/m3)

1.4

Flow TPH

135

Flow M3/sec

26.79

Line sizemm

800

Area M2

0.50

Velocity m/sec

53.28

Case2
Pressure (kg/cm2)

2.7

Temperature (deg c)

135

Density (kg/m3)

1.4

Flow TPH

160

Flow M3/sec

31.75

Line sizemm

900

Area M2

0.64

Velocity m/sec

49.9

Case3
Pressure (kg/cm2)

2.7

Temperature (deg c)

135

Density (kg/m3)

1.4

Flow TPH

80

Flow M3/sec

15.87

Line sizemm

600

Area M2

0.28

Velocity m/sec

56.13

Case4
Pressure (kg/cm2)

2.7

Temperature (deg c)

135

Density (kg/m3)

1.4

Flow TPH

40

Flow M3/sec

7.94

Line sizemm

450

Area M2

0.16

Velocity m/sec

49.90

Read Power plant and calculations for all such articles
Questions & Answers on steam blowing