2016 Webinar Sponsors - American Water Works Association · –Popularized by Parmakian. Many...

AWWA Webinar Program: Solutions for Water Hammer: Reduce Your Operational ImpactsWednesday, April 27, 2016

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Copyright © 2016 American Water Works Association

2016 Webinar Sponsors

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Webinar Moderator

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Alex Gerling

ReuseEngineerAmerican Water Works

Association

Alex Gerling is a Reuse Engineer with the American Water Works Association. Her responsibilities include reviewing, developing, and executing water reuse technical programs and supporting the Divisions and Committees of the Technical and Educational Council. She draws on her utility experience from the Western Virginia Water Authority where she provided technical support for a variety of water quality and reservoir oxygenation projects. She received a M.S. in Biological Sciences from Virginia Tech as well as a B.S. in Geoscience and a B.A. in Environmental Studies from Hobart and William Smith Colleges.

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Panel of Experts

7

Tom WalskiBentley Fellow,

Sr. Product ManagerBentley Systems, Inc.

Kevin LaptosRegional Planning Leader

Black & Veatch

Ferdous MahmoodSenior Hydraulic Engineer

Arcadis

Agenda

8

I. Hydraulic Transient Basics: An Overview

II. Water Hammer Analysis

III. Water Hammer / Surge Analysis Case Study for Pressurized Pipe

Tom Walski

Kevin Laptos

Ferdous Mahmood



Enter your question into the question pane at the lower right hand side of the screen.

Please include your name and specify to whom you are addressing the question.

Ask the Experts

99

Tom Walski Kevin Laptos Ferdous Mahmood

Hydraulic Transient Basics: An Overview

10

Tom WalskiBentley Fellow,

Sr. Product ManagerBentley Systems, Inc.



Overview

11

• What is a transient?

• Why do we care?

• How fast does it move?

• Why does it die-off?

• What causes it?

• What is column separation?

Learning Objectives

12

• At the end of this session you should be able to:

–Understand the basic characteristics of transients

–Recognise the risks of transients

– Learn about the transient calculation methods



What is a Transient?

13

Pre

ssu

re

Time

Shut off

New steady

state

Water Hammer Damage !

14



Water Hammer Damage !

15

Sub-atmospheric Pressure

16

a) Excavated Pipe Section

at Leakage Location

b) Pipe Joint Jammed by

Sand & Dust Residuec) Sample of Failed

Pipe Joint



Pressure Wave Properties

17

• Transients move as pressure waves

• a = wave speed

• The Wave Speed depends on:

– Fluid

– Pipe material

– Joints

– Presence of dissolved gas

– Anchoring

• Time of travel = L/a

• Characteristic time = 2L/a

Pressure Wave Speed Calculation

18

Korteweg equation for wave speed in a pipe:

Ev = Young's modulus (pipe)

E = bulk modulus (liquid)

= liquid density

= pipe support index

= Poisson's ratio

D/e = dimension ratio (DR)



19

Pressure Wave Decay

20

• Steady friction does not account for all damping mechanisms

190

210

230

250

0 5 10 15 20 25

Time (s)

He

ad

(m

)

Steady Quasi-Steady Transient

Steady

Quasi-steady

Unsteady

(Transient)



Characteristic Time: 2L/a

21

• Every system has a characteristic time, 2L/a:

– L is the longest possible path through the system (e.g. from pump to reservoir)

– a is the pressure wave speed: 300 to 1400 m/s

• 2L/a is the time required for a pulse to travel to the far end, then return:

– Fractions of a second for a short suction line

– Tens of seconds for a forcemain

– Minutes for long-distance transmission lines

System Response to Change

22

• Compared to 2L/a, valve movements or pump operations are:

– 0 = Instantaneous (e.g. phase change)

– ≤ 2L/a = Rapid, requires elastic theory (Method of Characteristics)

– > 2L/a = Gradual, solvable by rigid-column theory

– >> 2L/a = Slow, use rigid-column theory (or even Extended Period Simulation)



What Causes Transients?

23

Turbine

Reservoir PenstockGovernor

Generator

Gate

TurbineTailrace

Flow

H.G.L.

Reservoir PenstockGovernor

Generator

Gate

TurbineTailrace

Flow

H.G.L.

Pump

Valve

H.G.L.

Valve

H.G.L.

Valve

Check

Valve

Sump

Flow

Pump

H.G.L.

Check

Valve

Sump

Flow

Pump

H.G.L.

• Power failure

• Control/component failure

• Human error

• Start/Shift/Shut-down

• Valve operations & air

• Process changes, heat/cool

Any change in momentum that is “rapid” compared to the characteristic time: 2L/a (usually a few seconds)

What is the Impact of Transients?

24

• Joukowski’s / Allievi equation estimate transient pressure rise due to an instantaneous change in momentum:

–

• where:

– a = 1000 m/s concrete or

– a = 300 m/s plastic

• 1 m/s change (dV) can cause an upsurge (dH) of 100 m or 140 psi!

• Also be aware of thrust force, oscillations and resonance!

gadVdH /



Why Worry About Transients?

25

• Positive transients can break pipes

• Transients can cause pipes to shift

• Negative transients can collapse pipes

• Negative transients can suck contaminated water into pipes

• Injuries or death can occur if staff are present!

Assessing System Vulnerability

26

SURGE

ANALYSIS

TOOLS

Rule of Thumb or Rule of Dumb

Months

Days

Min

utes

“Hammer” Modeling (1990’s)

Computer Analysis (1970’s)

Graphical Analysis (1960’s)

Run HammerTM

to find out!

• SCADA systems can not usually measure transients fast enough

• Field data used to calibrate model

• Modern models make it possible to model an entire system



Unsteady Pipe Flow Equations

27

• Conservation of mass

• Conservation of momentum (e.g. energy)

x

V

g

a

x

HV

t

H

2

Vf

x

VV

t

V

gx

H

1

Methods to Analyze Transients

28

• Arithmetic, e.g. Joukowski equation

– Makes many assumptions but a useful rule-of-thumb

• Graphical method and design charts

– Popularized by Parmakian. Many charts by Fok. Time-consuming.

• Implicit method (two characteristic equations indexed by time)

• Linear analysis method

– Linearize friction to study oscillatory behavior and dampening

• Wave-plan method (discrete cumulative disturbances)

• Perturbation method (expands nonlinear friction term)

• Method of characteristics, e.g. MOC

– Converts full Navier-Stokes equations to solvable form

– Very widely-used and thoroughly calibrated/validated



Pressure Envelope

29

+ Transient Energy Calculated by Elastic

Water Column Theory (EWCT)

Transient Energy Calculated by Rigid

Water Column Theory (RWCT)Reservoir

Reservoir

Pipeline

Pump Station

Static HGLSteady HGL

Max. Head (Elastic)

Min. Head (Elastic)

Min. Head (Rigid)

Max. Head (Rigid)

Reservoir

Reservoir

Pipeline

Pump Station

Static HGLSteady HGL

Max. Head (Elastic)

Min. Head (Elastic)

Min. Head (Rigid)

Max. Head (Rigid)

Maximum Transient Head Envelopes for a Pumping System

Comparison of rigid and elastic theories:

Boundary Conditions & Reflections

30

• Boundary Conditions

– Orifices to atmosphere & consumption

– Dead-ends, reservoirs, and tanks (reflections)

– Operating equipment such as valves & pumps

• Changes in Topology

– Sudden change in diameter

– Branching

– Looping



Water Column Separation

31

• If pressure < vapor pressure, liquid vaporizes

• This is called column separation

• Water column rejoins once the pocket collapse

• Effect of water column separation

What is the Role of Pumps?

32

• Surges and Water Hammer happens if pumps start/stop too quickly

• Variable Speed pumps, soft starts, discharge control valves minimize transients during normal operation

• Set safe restart delays & ramp times for motor controller or PLC

• Pre-start safety audits, re-commissioning plans



The End

33

• Transients are important - You can model transients to prevent problems



Ask the Experts

3434




Kevin T. Laptos, PERegional Planning Leader

Black & Veatch

Water Hammer Analysis

35

• An effective approach for Water Hammer Analysis is needed

• This presentation will provide an approach to model and mitigate water hammer in water systems

Rationale

36



Learning Objectives

• Understand why water hammer analysis is needed

• Understand how transient models can be used to perform water hammer analysis

• Understand different methods for mitigating water hammer

37

Agenda

• Water hammer analysis objectives

• Model development

• Model validation

• Mitigation methods

38



Water Hammer Analysis Objectives

39

Why is Water Hammer Analysis Needed?

• Assess the potential for significant pressure transients

• Help assess the degree of risk in the system

• Develop and design/implement appropriate mitigation methods

40



4-Step Analysis Approach

41

Step 4:

Develop design criteria for selected mitigation strategies

Step 1:

Develop transient hydraulic model of system

Step 2:

Identify and analyze key transient scenarios

Step 3:

Develop and evaluate mitigation strategies for excessive pressure transients

Model Development

42



How are Transient Models Differentthan Steady-State and EPS Models?

• Simulate the propagation of pressure waves and resulting flow and pressure conditions due to transient causing events

• Additional system information is needed

43

Transient Model Development

44

• Add transient control equipment (i.e. air valves)

Pump Station

Reservoir

Reservoir

Combination Air Valves



Transient Model Development

45

• Add transient control equipment (i.e. air valves)

• Surge tanks

Pump Station

Reservoir

Reservoir

Surge Tank at Pump Station

46

Transient Model Development• Add transient control equipment (i.e. air valves)

• Surge tanks

• Pipeline wave speedsPump Station

Reservoir

Reservoir



47

Transient Model Development• Add transient control equipment (i.e. air valves)

• Surge tanks

• Pipeline wave speeds

• Additional pump (inertia, specific speed) and valve characteristics

Pump Station

Reservoir

Reservoir

Valve Opening (%)

% o

f M

axim

um

Cv

Model Validation

48



How can we Ensure Transient Models are Accurate?

• As with steady-state and EPS models…….calibration/validation is important

• However, challenges exist with transient models:• Instrumentation sample rate and data storage

• Reluctance to purposely cause a significant transient event

49

Example 1: Model Validation

50

0

100

200

300

400

500

600

700

800

900

1000

1100

1200

1300

1400

0 100 200 300 400 500 600 700 800 900 1000 1100 1200

Surg

e Ta

nk

Air

Vo

lum

e (f

t3)

Time (sec)

Manual collection of surge tank volume and timing data

Pump #1 ON Pump #2 ON Pump #2 OFF Pump #1 OFF

Field Data

Modeled Surge Tank Air Volume ft3



Example 2: Model Validation

51Collection of field data using existing instrumentation at PS

0

20

40

60

80

100

120

140

160

0 200 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400

Flo

w (

mgd

) /

Surg

e Ta

nk

Wat

er L

evel

(in

) /

Pre

ssu

re (

psi

)

Time (sec)

Pump #2 OFF Pump #2 ON Pump #5 ON Pump #4 ON Pump #4 OFF Pump #5 OFF Pump #2 OFF

PS Discharge Pressure (psi) Field Data+3 psi

-3 psi

+5%

-5%+5%

-5%

Surge Tank Water Level (in)

PS Flow Flow (mgd)

Example 3: Model Calibration

52

• Collection of field data using RADCOM pressure transient logger• Adjusted pump control valve closing speed to best match logger data• Validated pump/motor inertia

0

20

40

60

80

100

120

0 20 40 60 80 100

PS

Dis

char

ge P

ress

ure

(p

si)

Time (sec)

Field Recorded Pressure

Model Predicted Pressure

PS Power Loss



Example 4: Model Calibration

53

0

20

40

60

80

100

120

140

160

0 50 100 150 200 250 300

PS

Dis

char

ge P

ress

ure

(p

si)

Time (sec)

• Collection of field data using RADCOM pressure transient logger

• Adjusted pump startup sequencing and VFD settings to best match logger data

Pump #1 ON Pump #3 ONPump #2 ON

Field Recorded Pressure

Model Predicted Pressure

PS Power Loss

Mitigation Methods

54



Manually Operated Equipment

55

Hydrants and isolation valves

• Slow closing and opening

• Operator awareness and training are key

Automated Equipment & Facilities

56

Pump stations and control valves

• Proper analysis and design of transient control equipment is key



Transient Control Methods for Pumping Stations

57

Normal (i.e. hourly/daily) pump startup and shutdown

• Variable speed drives

• Pump control valves for constant speed pumps

• Pump control procedures (PLC)• Only start/stop one pump at a time

• Delay between consecutive pump starts/stops

Transient Control Methods for Pumping Stations

58

Emergency (i.e. power loss) pump shutdown

• High pressure control • Surge relief valves

• Surge anticipator valves

• Surge tanks

• Low pressure control• Air valves

• Surge tanks



Summary

59

Summary

• Numerous causes of water hammer in water systems

• Also numerous risks associated with both high and low pressure transients

• Transient models are indispensable for: • Assessing the potential for significant pressure transients

• Helping to assess the degree of risk in the system

• Developing and designing/implementing appropriate mitigation methods

60





Ask the Experts

6161


Water Hammer / Surge Analysis Case Study for Pressurized Pipe

62

Ferdous MahmoodSenior Hydraulic Engineer

Arcadis



Modeling Pressurized Pipes

63

• Steady state models

• master planning

• system improvements

• control valve settings

• Extended period models

• storage/production needs

• energy optimization

• operational improvements

• water age / disinfectant decay

• Surge models

• controlling high and low

pressures

Water Hammer in Pressurized Pipes

64

• Surge / Transient analysis

• Sudden changes in pressures

• Propagates through system

until dampened

• Damages system equipment

(pumps, valves, pipes)

• Damage may not be sudden

but develop over time due to

repeated surge or transient

episodes



Causes of Surge

65

• Pump operation – startup, shutdown or power failure

• Valve operation – rapid opening or closure

• Tank operation – loss of service

• Pipe filling and draining – air release

• Pipe breaks – rapid changes in demands

• Hydrant testing – rapid changes in demands

Preventing Pipeline Surge

66

• Proper selection of surge control components during design

• Proper operation of surge control devices and other components of system

• Proper maintenance of surge control devices

Surge / transient modeling



Case Study

67

• Pump Station

• 4 duty, 1 stand-by pumps

• Each pump 5,400 m3/hr, discharges to 30-inch line

• Valve opening and closing time controlled

• Pipeline

• 21.9 km (13.6 miles) pressurized pipe

• Standpipe on high ground

• 28.4 km (17.6 miles) gravity flow to WTP

Scenario 1 – No Check/Control Valves or Surge Prevention Devices

68

Maximum hydraulic grade

Minimum hydraulic grade

Steady state hydraulic grade

Pipe profile

Distance (m)

Ele

vation (

m)

Volu

me (

L)

Volu

me (

L)




69

Maximum transient pressure

Minimum transient pressure

Steady state pressure

Water Vapor pressure

Distance (m)

Pre

ssure

(psi)


70

Pre

ssure

(psi)

Flo

w (

m3/h

r)

Time (sec)



Scenario 2 – Check/Control Valves Closes in 2 Minutes

71




Pipe profile

Distance (m)

Ele

vation (

m)

Volu

me (

L)


72





Distance (m)

Pre

ssure

(psi)




73

Pre

ssure

(psi)

Flo

w (

m3/h

r)

Time (sec)

Scenario 4 – Check/Control Valve Closes in 5 sec; 24” Surge Relief Valve

74

Pre

ssure

(psi)

Flo

w (

m3/h

r)

Time (sec)




75





Distance (m)

Pre

ssure

(psi)


76

Pre

ssure

(psi)

Flo

w (

m3/h

r)

Time (sec)






Pipe profile

Distance (m)

Ele

vation (

m)

Volu

me (

L)

Scenario 5 – Check/Control Valve Closes in 5 sec; 24” Surge Relief Valve Two 150,000

gal Hydro Pneumatic Tanks

77





Distance (m)

Pre

ssure

(psi)



78





79

Pre

ssure

(psi)

Flo

w (

m3/h

r)

Time (sec)

Scenario 7 – Check/Control Valve Closes in 5 sec; 24” Surge Relief Valve Four 120,000


80




Pipe profile

Distance (m)

Pre

ssure

(psi)

Volu

me (

L)





81





Distance (m)

Pre

ssure

(psi)

Volu

me (

L)



82

Pre

ssure

(psi)

Flo

w (

m3/h

r)

Time (sec)






Pipe profile

Distance (m)

Pre

ssure

(psi)

Volu

me (

L)

Scenario 8 – Check/Control Valve Closes in 5 sec; 24” Surge Relief Valve Six 120,000 gal

Hydro Pneumatic Tanks

83





Distance (m)

Pre

ssure

(psi)

Volu

me (

L)



84





85

Pre

ssure

(psi)

Flo

w (

m3/h

r)

Time (sec)




Pipe profile

Distance (m)

Pre

ssure

(psi)

Volu

me (

L)

Scenario 9 – Check/Control Valve Closes in 5 sec; 24” Surge Relief Valve Six 120,000 gal Hydro Pneumatic Tanks with 4” by-pass

86







Distance (m)

Pre

ssure

(psi)

Volu

me (

L)


87


88

Pre

ssure

(psi)

Flo

w (

m3/h

r)

Time (sec)






Pipe profile

Distance (m)

Pre

ssure

(psi)

Volu

me (

L)

Scenario 13 – Check/Control Valve Closes in 5 sec; 24” Surge Relief Valve Five 120,000 gal

Hydro Pneumatic Tanks with 4” by-pass

89





Distance (m)

Pre

ssure

(psi)

Volu

me (

L)

90

Scenario 13 – Check/Control Valve Closes in 5 sec; 24” Surge Relief Valve Five 120,000 gal

Hydro Pneumatic Tanks with 4” by-pass



Case Study 2

91

• Pump Station

• 2 duty, 1 stand-by

pumps

• Each pump 3

mgd, discharges

to 10-inch line

• Valve opening and

closing time

controlled

• Pipeline

• 9,500 feet

pressurized pipe

• 3 MG storage tank

Scenario A - Four 2-inch Air Valves Only with Pump Check Valve Closing Immediately

92

Existing four 2-inch air

valves only with pump check

valve closing immediately

Ele

vation (

ft)

Volu

me



Scenario A - Four 2-inch Air Valves Only with Pump Check Valve Closing Immediately

93

Hyd

raulic

Gra

de (

ft)

Flo

w (

m3/h

r)

Time (sec)

Air V

apor

Volu

me (

gal)

Scenario B - Existing Four 4-inch Air Valves and 8-inch Surge Relief Valve

94

Ele

vation (

ft)

Volu

me



Scenario B - Existing Four 4-inch Air Valves and 8-inch Surge Relief Valve

95

Hyd

raulic

Gra

de (

ft)

Flo

w (

m3/h

r)

Time (sec)

Air V

apor

Volu

me (

gal)

Ele

vation (

ft)

Volu

me

Scenario C - Two 2-inch Air Valves and Four 4-inch Air Valves AND 5000 gal Surge Tank with

12” Inlet

96



Scenario C - Two 2-inch Air Valves and Four 4-inch Air Valves AND 5000 gal Surge Tank with

12” Inlet

97

Hyd

raulic

Gra

de (

ft)

Flo

w (

m3/h

r)

Time (sec)

Air V

apor

Volu

me (

gal)

Scenario C - Two 2-inch Air Valves and Four 4-inch Air Valves AND 5000 gal Surge

Tank with 12” Inlet

98

Hyd

raulic

Gra

de (

ft)

Flo

w (

m3/h

r)

Time (sec)

Air V

apor

Volu

me (

gal)



Surge Analysis Summary for Pressurized Pipes

99

Options for Surge Prevention

100

• Design / install surge protection devices

Surge tanks, pump control valves, pump flywheel, air release valves and vacuum breakers, pressure relief valves, others

• Modify pump and valve operation set points, timing

• Reduce pipe velocity larger diameter pipe

• Reduce wave speed different pipe material

• Increase pump inertia flywheel

• Increase pipe pressure rating higher class pipe

• Provide additional pressure relief pump bypass line

• Reduce elevations changes pipe re-routing



Surge / Transient Pressure Modeling

101

• Analyze existing transient pressures for specific operational events

• Mitigate transients using appropriate devices such as:

• Surge tanks, pump control valves, pump flywheel, air release valves and vacuum breakers, pressure relief valves, others

• Conduct detailed surge analysis

• Hand calculations and charts

• Transient computer models (Hammer, Infosurge, CFD models can be used but time consuming)

• Observe hydraulic behavior of each component and their interaction



Ask the Experts


102



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105

Presenter Biography Information

106

Tom Walski has 40 years of experience in water and wastewater design and operation. He is currently senior product manager for Bentley Systems and has previously served as civil engineer for the Army Corps of Engineers, distribution system manager for the City of Austin, Tex., executive director the Wyoming Valley Sanitary Authority, and engineering manager for Pennsylvania American Water. He has written several books and hundreds of journal and conference papers on many aspects of water distribution systems.

Based in Charlotte, NC. Specializes in planning and modeling of water distribution and wastewater collection systems and hydraulic transient analysis. 26 years of experience in engineering practice and management involving the planning, design, construction, operation, and rehabilitation, of water and wastewater systems.

Mr. Mahmood is a senior hydraulics engineer at Arcadis specializing in hydraulics and water quality modeling of distribution systems and treatment plants. He conducts various types of modeling - hydraulics, computational fluid dynamics (CFD), surge, and water quality – for master planning of water distribution systems and for evaluating and optimizing design of treatment plants. Mr. Mahmood assisted USEPA with the development of the Initial Distribution System Evaluation (IDSE) Guidance Manual, and is a co-author for AWWA M32 Manual on Computer Modeling of Distribution Systems.



107

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