WATER NETWORK DESIGN
The water water supp ly cycle
D A M S
The water water supp ly cycle
D A M S
Introduction Water Distribution systems play an important role in supplying water for our everyday needs. Proper installation and maintenance of these systems depends on: •the operator’s knowledge of the system, •regular inspection, And equipment maintenance. maintenance. • And
Pipes and valves need to be properly selected to m eet the design specifications of each water system.
Types Ty pes of Piping Water Distribution systems demand piping that is soli d, resilient, durable and is resistant to corrosion over a long l ong period of time.
It is necessary that piping not chemically react with water.
The lighter the piping used, the easier it is to handle.
Pressure rating rating of the pi ping used must also be adequate for each type of water distribution system.
Long ago, distribution systems used woods for piping material but it could not withstand the water pressure.
Most of today’s water distribution systems have m oved to a cast-iron steel piping (CIP).
During the 1990’s, a gray cast iron type of piping was introduced.
Stresses in p ipes
Internal Pressure produces hoop stress And long itud inal st ress
R: Radius P: Internal pressure T: pipe wall thickness
h=r x P/t
l = r x P /2 t
Stresses in p ipes Water Hammer results from the sudden stopping or slowing of flow in a conduit. The kinetic energy of the water moving through the pipe in converted into potential energy.
P U M P
S H U T D O W N
Pump run down resulting from planned shutdown or C electric power failure results O N D I in column separation T I O N S
Column returns and shock pressure occurs
P U M P
S
Shock pressure occurs when pumping operation begins abruptly and fluid is supplied to a static column
T A R T U P
C O N D I T I O N
Pipe Beddin g
-
Pipe Material
Metallic Pipes
Cast iron
Ductile iron
Steel (carbon steel)
Concrete pipes
Concrete Cylinder Pipes (CCP) Asbestos cement
Plastic pipes
PVC
PE
GRP
Metallic Pipes – Difference between Grey Iron – Ductile Iron – Steel All metallic pipes are made in iron, the difference resides in the carbon content: Material
Definition
Standard US
Other
Ductile
type of cast iron used
AWWA C150/A21.50 American
EN 555:2002 Ductile
Iron
for pipes, fittings and
National Standard for the Thickness
iron pipes fittings,
accessories in which
Design of Ductile-Iron Pipe
accessories and
graphite is present
AWWA C110/A21.10, American
their joints for
primarily in
National Standard for Ductile-Iron
water pipelines –
spheroidal form
and Gray-Iron Fittings 3 in. through
Requirements and
58 in. (75 mm thru 1220 mm for
test methods
Water and Other Liquids
ISO2531:2009,
AWWA C115/A21.15, American
Ductile iron pipes,
National Standard for Flanged
fittings, accessories
Ductile-iron Pipe with Threaded
and their joints for
Flanges
water applications
Steel
ASME B31.5-2006 Pipeline Transportation Systems for Liquid Hydrocarbons and Other Liquids
Ductile Iron
DI pipe is a type of piping that is even sronger than CI pipe.
Although
DI is heavy, CI is heavier.
Transmission lines are often made of DI because it provides a long service life.
Furthermore, inside cement lining of DI can help tuberculation (growth of clumps of materials).
DI is less prone to corrosion; additional thickness is provided as a safety factor to
allow for corrosion. Additional cost in material (at least 2 to 3 times more in weight if compared to the same steel pipe).
DI is generally accepted as reliable piping material.
Ductile Iron
Ductile Iron - Definitions Nominal Pressure - PN numerical designation, which is a convenient rounded
number, used for reference purposes Nominal size – DN
The standard nominal sizes, DN, of pipes and fittings are the following: 50, 50, 60, 65, 80, 100, 125, 150, 200, 250, 300, 350, 500, 550, 500, 600, 700, 800, 900, 1000, 1100, 1200, 1500, 1500, 1600, 1800, 2000, 2200, 2500 and 2600
DI – Thick ness cl ass (EN 555:2002) K classes for pi pes and fitt ings
The nominal iron wall thickness of pipes and fittings is given as a funct ion of the nominal size, DN, by the following formula with a minimum of 6 mm f or pipes and 7 mm for fittings: e =K.(0.5 + 0.001 DN)
where e
is the nominal wall thickness. in millimetres ;
DN
is the nominal size (in millimiters);
K
is a coefficient used for the determination of the thickness . It is selected from a series of whole numbers : 8, 9 , 10, 11, 12, 15,…
Steel Pipe
Steel is primarly used where high pressure is required.
Steel piping is light weight, easy to install and t ransport.
It has a low resistance to external pressures; therefore, it requires a lining or
coating to maintain a long service life.
The exterior of steel piping requires a protected wrap such as galvanized or epoxy
to prevent damage from outside elements.
Steel pipe does not allow for any corrosion factor. Consequently excellent
maintenance is needed: either regular painting or cat hodic protection.
Steel pipes
Steel Grades
Steel Pipes – Wall t hickness calculation The internal pressure design wall thickness t in mm of the steel pipe is calculated by the following equation:
t
P D i 20S
Where: t
pressure design wall thickness
[mm]
Pi
internal design gage pressure
[bar]
D
outside diameter of pipe
[mm]
S
applicable allowable stress value
[MPa]
=0.72 . E.SYMS
[-]
E
weld joint factor [=1]
[-]
SMYS
specified minimum yield strength of the pipe
[MPa]
Protection of steel pip es against corro sion
Internal protection
fusion bonded epoxy coating Cement mortar lining Polypropelene coating
External protection:
In
Fusion bonded epoxy coated Polypropelene coating
addition, in order to extend pipelinelife span, it is highly recommended to provide
cathodic protection:
Induced currents Scarifying anodes
Asbesto s Cement
Light weight
Very economical price
Fire-proofing
Resistance to detoriation, and high tensile strength
Risk of breaking durin g installation and need for special equipment
Causes cancer and has been banned from used.
Concrete Pipes: Concrete Cylin der Pipes
Concrete piping has grown in popularity because it has the advantages of strength
and durability, plus it is available in many diameters.
It has been found to be in good condition even after a one hundred year work life.
Prestressed concrete is durable and can take pressures up to 250psi.
Concrete that is not pre-stressed can only take up to 50 psi.
It is extremely heavy so shipping is not economical and special hauling and lifting
equipment is required.
Plastic Pipes
Can withstand internal & external pressures
Free from harmful material that can alter the taste and odor of potable water
Should not be used where the soil become contaminated by petroleum products,
since permeation of harmful chemical could occur.
It has a nice flowing smooth interior
It cannot be damaged by corrosion.
For ex., Polyvinyl Chloride Piping (PVC) isa very user-friendly to pipe fitters and
easily maintained.
Easy to use and install
When buried, PVC is hard to locate since it is nonconductive.
PVC is not feasible for above ground use in direct sunlight.
Valves: Type
Valves are extremely important in the control of water systems.
Valves need periodic maintenance to make sure they are working properly and are not damaged.
Valves should be placed in locations in the water systems that are easily accessible for repairs & emergency shut off situations.
Valves should always be stored indoors and in fully closed position when possible.
Valves Types:
Gate valve Globe valve Butterfly valve Ball valve Check valve
Parts o f a v alve
1. Closure member: part of the valve that closes flow (disk, ball, gate, etc.). 2. Actuator: means of operating the valve – hand, gear, chain wheel, motor, solenoid, pressure and flow of the media, air pressure. 3. End fitting: must be specified when buying the valve - butt weld end, compression flange, pipe thread, quick disconnect 5. Material: closure member, housing, seat – stainless steel 5. Packing/seals: seals stem, replaced 6. Seat: where the closure members seals against the valve housing
Gate Valve
Sliding disk, perpendicular to flow
Applications: Stop valves, (not throttling), high pressure and temp, not for slurries, viscous fluids
Advantages – low pressure drop when fully open, tight seal when closed, free of contamination buildup
Disadvantages – vibration when partially open, slow response and large actuating force
Butt erfly valve A
butterfly valve is a rotary motion valve. The main purpose of butterfly valve is used to stop,
regulate, and start fluid flow. This type of valve is easily and quickly operated because there is a 90 degree rotation of the handle which moves the disk from a fully closed to fully opened position. Butterfly valves are available in various sizes and materials. The
larger sized butterfly valves are actuated by hand wheels which are connected to the stem
through gears and they provide mechanical advantage at the expense of speed.
The
butterfly valve consists of only five main com ponents:
Body: Disc:
These valves have bodies that fit between two pipe flanges.
The disk is the flow closure member of a butterfly valve.
Stem:
The stem of the butterfly valve is either a one-piece shaft or a two-piece, also known as
split-stem design. Seat:
The seat of a butterfly valve utilizes an interference fit between the disk edge and the seat
to close or to shutoff. Operator
Butterfly valve – Centric valve
Butterfly valve – Eccentric Valve
• Rotating disk on a shaft, in a housing • Low pressure, large diameter lines where leakage is unimportant •Advantages – low pressure drop, small and light weight •Disadvantages – high leakage, high actuation forces so limited to low pressures
•Globe valve
• Typically used in pipes that are four inches in diameter or smaller. •Seldom used in water distribution systems, mainly for household plumbing •Throttling, general purpose flow control valve
Ball valve
•
Sphere with a port in a housing, rotate to expose channel.
• · Applications: Flow control, pressure control, shutoff, corrosive fluids, liquids, gases, high temp. • Advantages – low pressure drop, low leakage, small, rapid opening • · Disadvantages – seat can wear if used for throttling, quick open may cause hammer
Valves Symbols
Butterfly Valve Ball Valve Gate Valve Globe Valve
Valve functi on
Definitions
What do we mean by on/off/modulating?
On/Off means valve is either open or closed. Example may be a float valve, an altitude valve or a solenoid valve.
Modulating means the valve is changing position, moving open and closed to maintain a desired set point. Example is pressure reducing, float valve, sustaining valve.
Regulation:
Pressure control valve (down-stream)
Pressure sustaining (up-stream)
Flow control
Altitude valve
Contr ol Valves Types Control Valve Type Pressure reducing Pressure sustaining Pressure breaker Flow control Vacuum breaker Throttle control Float Altitude User defined or General purpose Pressure relief
Description of Control Valve Operation Work to maintain a constant downstream pressure that matches the PRV setting. Maintain a constant upstream pressure while downstream pressure fluctuates. Force a specified pressure drop to occur across the valve. Attempt to control flow through a pipe, regardless of upstream and downstream pipe pressures. Allows air to enter a pipeline when the pressure drops to atmospheric level. Used to adjust flows or to control pressures in the system. Behave as an automatic flow control valve (control rate of flow) in which the regulating principle is the tank water level. Are positioned on all storage tanks to automatically close when the water in the tank reaches its minimum level (tank is em pty) or maximum level (tank is full), and to stay open w ithin the intermediate range. Used to model turbines, well draw-down, or reduced-flow backflow prevention valves. Prevent excessive pressures in a pipe.
Valve op erations There are four basic methods of valve operations:
Manual
Electrical
Hydraulic
Pneumatic
Power Actuators can be used to operate the valves. Actuator is a device responsible for activating a mechanical process. Valve actuators should be operated slowly. Water hammer may occur if valve actuators are operated with too much speed.
Valve op erations
Cavitation “Cavitation
is a two stage phenomenon of liquid flow. The first stage is the
formation of voids or cavities within the liquid s ystem; the second stage is the collapse or implosion of these cavities back into an all-liquid state” Instrument Society of America
Typically
occurs in high pressure drop and low flow applications when valve is
operating close to the seat
An ti -cavitati on valves
P2
Pv
P1
P2
Sample of cavitation index graph for a MONOVAR valve
P1 : Absolute upstream pressure measured in practice one pipe diameter above the valve, P2 : Absolute pressure measured 10 pipe diameters below t he valve and correct ed for friction losses between points 1 and 2, PV : Vapor pressure of the liquid at the operating temperature. Different types of valve have different behaviour in face of cavitation, below is a classification from the most sensitive to the less sensitive: •gate valve •ball valve •butterfly valve •special valves (MONOVAR from SAPAG or throttling valve from Glenfield).
Pipe Couplings & Flange Adapters
•No transmission of forces from pipe to coupling / Flange Adapter
Role of a fl owm eter A
flowmeter is an instrument used to measure linear, nonlinear, mass or volumetric
flow rate of a liquid or a gas. The
basis of good flowmeter selection is a clear understanding of the requirements
of the particular application. Here are some key questions which need to answered before selecting a flowmeter: Do
you require a local display on the flow meter or do you need an electronic signal
output? What
is the minimum and maximum flowrate for the flow meter?
What
is the minimum and maximum process pressure?
What
is the minimum and maximum process temperature?
