Pipe Design

1. Water Transportation:
Hydraulics, Pipe Design
Hari Prasad Sharma
info@shamahari.com.np

2. Factors Determining Pipe Flow Rates
Hydraulics is related with the;
 properties and behavior of fluids
 its state at rest or in motion
The factors that affect the flow of water in pipes
are;
 Cross sectional area;
 Roughness of the pipe’s inner surface;
 Condition and type of flow;
 Obstructions; and
 Energy head

3. Energy Grade Line & Hydraulic Grade Line

4. Different Terminology in Pipe Design
To understand the behavior of water as it flows through
the pipes; we should know
• Hydraulic Gradeline (HGL) - The Hydraulic Grade Line
(HGL) is an imaginary line that connects the points on
which the water would rise in a piezometer tube if
inserted in any place along the pipe.
• Energy Grade Line (EGL) - the summation of elevation
head (H) of the pipe, pressure head (Hp) and velocity
head (Hv) with reference to a fixed datum.
• Equivalent Length (EL) - the length of fittings,
appurtenances, etc. reduced to a specific length of
straight pipe with same diameter

5. Water Pressure
The force represents the weight of a column of water above a
certain point.

6. Static Water Pressure
Static water pressure or potential pressure
available - pressure in the system when water is
not flowing and produced by;
 Placing the water at an elevation above the
location of water use (for example, in an elevated
reservoir;
 Imparting energy to the water through a pump;
and
 Air pressure in hydro-pneumatic tanks

7. Head Loss in Pipe
• Head Loss - Shear stress is developed
between the water and the pipe wall when
water is flowing
• Calculated using following formulas;
 Darcy-Weisbach formula
 Hazen-Williams formula
 Mannings formula
 Colebrook and White Formula
 Combined Darcy-Weisback and Colebrook-White
equation.

8. Darcy-Weisbach Equation
According to Darcy – Weisbach
HL = (LV2/D2g)
Where;
HL - Pressure Drop or Head Loss
 - Pipe friction coefficient
L – Length of Pipe
V – Velocity of Fluid
D – Inner Diameter of Pipe
g - Gravity
Substituting the
above formula;
V = Q/A;
A=𝜋𝐷2
/4
8  LQ2
D5 = -----
²ghL

9. Hazen Williams Formula

10. Colebrook and White Formula
1 k 2.51
----- = - 2 log (------ + --------- )
0.5 3.7 x D Re x 0.5
Where Re = VD/µ = Reynold's Number
k/D = Relative Roughness Ratio
f = Friction Factor
, are k, D, µ which depends on temperature, and velocity V
Both sides of the equation (6) contains . It, therefore, can be
solved only by an iterative method

11. Manning formula
The Manning formula states:
V - is the cross-sectional average velocity (m/s)
K - is a conversion factor of (Length1/3/Time), 1 m1/3/s for SI
n - is the Manning coefficient, it is unitless
Rh - is the hydraulic radius (m)
S - is the slope of the water surface or the linear hydraulic head
loss (L/L) (S = hf/L)
For Circular Diameter Manning Equation is
D = 16 Q*n/S3/8

12. Hydraulic Grade Line

13. Fundamentals of Transmission System
• Transport water from water source to treatment
plant or to service reservoir.
• Some arrangement or structure to inter water
into the transmission – Intake.
• Alignment of transmission – short distance,
pressure in the pipe should be maintained as per
requirements ( 250>P>10).
• Some time for the economy transmission will
design in residual pressure not in static pressure.

14. Pipeline Design Steps
• Determination of the problem
 The characteristics of the fluid to be carried, including the
flow rate and the allowable headloss
 The location of the pipelines: its source and destination, and
the terrain over which it will pass, the location of separator
station and the power plant;
 The design code to be followed
 The material to be used.
• The determination of a preliminary pipe route, the line length
and static head difference.
• Pipe diameter based on allowable headloss;
• Support and anchor design based on reaction found in the
structural analysis.

15. Transmission Design - Example
• Data requires for transmission design
• Flow to be transmitted – lit/sec ; daily demand
flow without peak factor
• Length to be transmitted
• Pipe material to be used for transmission
• Level difference – starting level, intermediate
levels and end level
• Head loss calculation formulas

16. Example of Panchkhal WS Project
Sub-project : Panchkhal Water Supply Project, Kavrepalanchok
Line
Lengt
h Reduced Level Level
Total Max.
Pipe Used
Sr. Chainage Actual Design Flow Up Down Differ-
Head Static
HDPE
GI
Head Residual HGL Flow
No. m. m. m. l/s m. m. ence Avail. Press. O.D. Press. I.D. N.B. Loss Head m. Velocity
m. m m mm kg/cm² mm mm m. m. m/s
Proposed Transmission Line from ...... Stream For RVT No.
1Source to 120 120 132 18.10 1670.00 1662.00 8.00 8.00 8.00 225 4 201.90 0.21 7.79 1669.79 0.57
2ch 120 to 300 180 198 18.10 1662.00 1645.00 17.00 24.79 25.00 225 4 201.90 0.32 24.46 1669.46 0.57
3ch 300 to 435 135 149 18.10 1645.00 1648.00 -3.00 21.46 22.00 225 4 201.90 0.24 21.22 1669.22 0.57
4ch 435 to 650 215 237 18.10 1648.00 1634.00 14.00 35.22 36.00 225 4 201.90 0.39 34.84 1668.84 0.57
5ch 650 to 710 60 66 18.10 1634.00 1640.00 -6.00 28.84 30.00 225 4 201.90 0.11 28.73 1668.73 0.57
6ch 710 to 885 175 193 18.10 1640.00 1605.00 35.00 63.73 65.00 225 10 173.40 0.66 63.07 1668.07 0.77
7ch 885 to 915 30 33 18.10 1605.00 1616.79 -11.79 51.28 53.21 225 6 191.40 0.07 51.21 1668.00 0.63
8ch 915 to 1095 180 198 18.10 1616.79 1622.72 -5.93 45.28 47.28 225 6 191.40 0.42 44.86 1667.58 0.63
9ch 1095 to 1185 90 99 18.10 1622.72 1635.06 -12.34 32.52 34.94 225 4 201.90 0.16 32.36 1667.42 0.57
10ch 1185 to 1305 120 132 18.10 1635.06 1631.75 3.32 35.67 38.25 225 4 201.90 0.21 35.46 1667.21 0.57
11ch 1305 to 1455 150 165 18.10 1631.75 1644.29 -12.54 22.92 25.71 225 4 201.90 0.27 22.65 1666.94 0.57
12ch 1455 to 1515 60 66 18.10 1644.29 1645.34 -1.05 21.60 24.66 225 4 201.90 0.11 21.49 1666.83 0.57
13ch 1515 to 1635 120 132 18.10 1645.34 1627.39 17.95 39.44 42.61 225 6 191.40 0.28 39.17 1666.55 0.63
14ch 1635 to 1815 180 198 18.10 1627.39 1577.88 49.50 88.67 92.12 225 10 173.40 0.68 87.99 1665.88 0.77
15ch 1815 to 1875 60 66 18.10 1577.88 1585.73 -7.84 80.15 84.27 225 10 173.40 0.23 79.92 1665.65 0.77
16ch 1875 to 2038 163 179 18.10 1585.73 1601.93 -16.20 63.73 68.07 225 10 173.40 0.61 63.11 1665.04 0.77
17ch 2038 to 2193 155 171 18.10 1601.93 1605.75 -3.82 59.29 64.25 225 10 173.40 0.58 58.71 1664.46 0.77

18. Things to be remembers in
Transmission Design
• Residual Pressure to be maintained within 10
to 25 m; minimum 5 m
• Velocity to be greater than 0.35 m/sec and
should not be higher than 3.5 m/sec
• Washouts in the lowest points and air valves
in the required places should be placed.
• Other structures – retaining walls, supporting
pillars, thrust blocks to be designed