Solutions for Water Hammer

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Alex Gerling

Reuse Engineer American 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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6 Panel of Experts

Tom Walski Kevin Laptos Ferdous Mahmood Bentley Fellow, Regional Planning Leader Senior Hydraulic Engineer Sr. Product Manager Black & Veatch Arcadis Bentley Systems, Inc.

7 Agenda

I. Hydraulic Transient Basics: An Tom Walski Overview Kevin Laptos II. Water Hammer Analysis

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

8 Ask the Experts

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.

9 Hydraulic Transient Basics: An Overview

Tom Walski Bentley Fellow, Sr. Product Manager Bentley Systems, Inc.

10 Overview

• 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?

11 Learning Objectives

• 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

12 What is a Transient?

Shut off Pressure

New steady state

Time

13 Water Hammer Damage !

14 Water Hammer Damage !

15 Sub-atmospheric Pressure a) Excavated Pipe Section b) Pipe Joint Jammed by c) Sample of Failed at Leakage Location Sand & Dust Residue Pipe Joint

16 Pressure Wave Properties • 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

17 Pressure Wave Speed Calculation Korteweg equation for wave speed in a pipe:

Ev = Young's modulus (pipe) E = bulk modulus (liquid) ρ = liquid density Ψ = pipe support index µ = Poisson's ratio D/e = dimension ratio (DR)

18 19 Pressure Wave Decay • Steady friction does not account for all damping mechanisms 250 Steady Quasi-Steady Transient

Steady

230 Quasi-steady

Unsteady

Head (m) (Transient)

210

190 0 5 10 15 20 25 Time (s)

20 Characteristic Time: 2L/a • 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

21 System Response to Change • 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)

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

• Power failure • Start/Shift/Shut-down • Control/component failure • Valve operations & air • Human error • Process changes, heat/cool

H.G.L. H.G.L. H.G.L.

Reservoir Penstock Governor Pump Check Generator Valve Valve Flow Flow Sump Gate Tailrace Turbine

Pump Turbine Valve

23 What is the Impact of Transients?

• Joukowski’s / Allievi equation estimate transient pressure rise due to an instantaneous change in momentum: – dH = dV (a / g) • 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!

24 Why Worry About Transients?

• 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!

25 Assessing System Vulnerability • 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 “Hammer” Modeling (1990’s)

Run HammerTM to find out!

Minutes Computer Analysis (1970’s) SURGE ANALYSIS TOOLS Days

Months Graphical Analysis (1960’s)

Rule of Thumb or Rule of Dumb

26 Unsteady Pipe Flow Equations

δH δH a 2 δV • Conservation of + V = − mass δt δx g δx

• Conservation of δH 1 δV δV  = −  + V + f (V ) momentum (e.g. δx g  δt δx  energy)

27 Methods to Analyze Transients • 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

28 Pressure Envelope Maximum Transient Head Envelopes for a Pumping System

Comparison of rigid and elastic theories:

Max. Head (Elastic)

Max. Head (Rigid) Reservoir Steady HGL Static HGL

Min. Head (Rigid) Min. Head (Elastic)

Pipeline

Pump Station + Transient Energy Calculated by Elastic Water Column Theory (EWCT) Reservoir Transient Energy Calculated by Rigid Water Column Theory (RWCT)

29 Boundary Conditions & Reflections • 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

30 Water Column Separation • If pressure < vapor pressure, liquid vaporizes • This is called column separation • Water column rejoins once the pocket collapse • Effect of water column separation

31 What is the Role of Pumps? • 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

32 The End

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

33 Ask the Experts

34 Water Hammer Analysis

Kevin T. Laptos, PE Regional Planning Leader Black & Veatch

35 Rationale

• An effective approach for Water Hammer Analysis is needed

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

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

Step 4:

Develop Step 3: design criteria for Develop and selected Step 2: evaluate mitigation mitigation strategies Step 1: Identify and strategies for analyze key excessive Develop transient pressure transient scenarios transients hydraulic model of system 41 Model Development

42 How are Transient Models Different than 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 • Add transient control equipment (i.e. air valves)

Pump Station

Reservoir

Combination Air Valves

Reservoir

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

Pump Station

Reservoir

Surge Tank at Pump Station

Reservoir

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

• Pipeline wave speeds Pump Station

Reservoir

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

• Pipeline wave speeds Pump Station • Additional pump (inertia, specific speed) and valve characteristics v C Reservoir % of Maximum

Reservoir

Valve Opening (%)

47 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

1400 1300 Field Data 1200 1100 Pump #1 ON Pump #2 ON Pump #2 OFF Pump #1 OFF ) 3 1000 900 Modeled Surge Tank Air Volume ft3 800 700 600 500

Surge Tank Air Volume (ft Air Volume Tank Surge 400 300 200 100 0 0 100 200 300 400 500 600 700 800 900 1000 1100 1200 Time (sec)

50 Manual collection of surge tank volume and timing data Example 2: Model Validation 160 PS Discharge Pressure (psi) Field Data +3 psi 140

-3 psi 120

100

Pump #2 OFF Pump #2 ON Pump #5 ON Pump #4 ON Pump #4 OFF Pump #5 OFF Pump #2 OFF 80

60 Surge Tank Water Level (in) +5% 40

) / Surge Tank Water Level (in) / Pressure (psi) Pressure (in)Level / Water Tank ) Surge / -5% +5% mgd 20 PS Flow Flow (mgd) -5% Flow ( Flow 0 0 200 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400 Time (sec)

51 Collection of field data using existing instrumentation at PS Example 3: Model Calibration

120 PS Power Loss Field Recorded Pressure 100 Model Predicted Pressure

40 PS Discharge Pressure (psi) Pressure PS Discharge 20

0 0 20 40 60 80 100 Time (sec)

• Collection of field data using RADCOM pressure transient logger • Adjusted pump control valve closing speed to best match logger data • Validated pump/motor inertia 52 Example 4: Model Calibration

160 Pump #1 ON Pump #2 ON Pump #3 ON 140

120 PS Power Loss

100

PS Discharge Pressure (psi) Pressure PS Discharge 40 Field Recorded Pressure 20 Model Predicted Pressure 0 0 50 100 150 200 250 300 Time (sec) • Collection of field data using RADCOM pressure transient logger • Adjusted pump startup sequencing and VFD settings to best match logger data 53 Mitigation Methods

54 Manually Operated Equipment

Hydrants and isolation valves • Slow closing and opening • Operator awareness and training are key

55 Automated Equipment & Facilities

Pump stations and control valves • Proper analysis and design of transient control equipment is key

56 Transient Control Methods for Pumping Stations

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

57 Transient Control Methods for Pumping Stations

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

58 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

61 Water Hammer / Surge Analysis Case Study for Pressurized Pipe

Ferdous Mahmood Senior Hydraulic Engineer Arcadis

62 Modeling Pressurized Pipes

• 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

63 Water Hammer in Pressurized Pipes

• 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

64 Causes of Surge

• 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

65 Preventing Pipeline Surge

• Proper selection of surge control components during design Surge / transient • Proper operation of surge modeling control devices and other components of system • Proper maintenance of surge control devices

66 Case Study • 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

67 Scenario 1 – No Check/Control Valves or Surge Prevention Devices VolumeVolume (L) (L) Elevation(m) Maximum hydraulic grade Steady state hydraulic grade Minimum hydraulic grade Pipe profile

Distance (m) 68 Scenario 1 – No Check/Control Valves or Surge Prevention Devices

Maximum transient pressure Steady state pressure Minimum transient pressure Water Vapor pressure Pressure (psi)

Distance (m) 69 Scenario 1 – No Check/Control Valves or Surge Prevention Devices Pressure (psi) ) hr Flow (m3/Flow

Time (sec)

70 Scenario 2 – Check/Control Valves Closes in 2 Minutes Volume (L) Elevation(m) Maximum hydraulic grade Steady state hydraulic grade Minimum hydraulic grade Pipe profile

Distance (m) 71 Scenario 2 – Check/Control Valves Closes in 2 Minutes

Maximum transient pressure Steady state pressure Minimum transient pressure Water Vapor pressure Pressure (psi)

Distance (m)

72 Scenario 2 – Check/Control Valves Closes in 2 Minutes Pressure (psi) ) hr Flow (m3/Flow

Time (sec)

73 Scenario 4 – Check/Control Valve Closes in 5 sec; 24” Surge Relief Valve Pressure (psi) ) hr Flow (m3/Flow

Time (sec)

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

Maximum transient pressure Steady state pressure Minimum transient pressure Water Vapor pressure Pressure (psi)

Distance (m) 75 Scenario 4 – Check/Control Valve Closes in 5 sec; 24” Surge Relief Valve Pressure (psi) ) hr Flow (m3/Flow

Time (sec)

76 Scenario 5 – Check/Control Valve Closes in 5 sec; 24” Surge Relief Valve Two 150,000 gal Hydro Pneumatic Tanks Volume (L) Elevation(m) Maximum hydraulic grade Steady state hydraulic grade Minimum hydraulic grade Pipe profile

77 Distance (m) Scenario 5 – Check/Control Valve Closes in 5 sec; 24” Surge Relief Valve Two 150,000 gal Hydro Pneumatic Tanks

Maximum transient pressure Steady state pressure Minimum transient pressure Water Vapor pressure Pressure (psi)

Distance (m) 78 Scenario 5 – Check/Control Valve Closes in 5 sec; 24” Surge Relief Valve Two 150,000 gal Hydro Pneumatic Tanks Pressure (psi) ) hr Flow (m3/Flow

Time (sec)

79 Scenario 7 – Check/Control Valve Closes in 5 sec; 24” Surge Relief Valve Four 120,000 gal Hydro Pneumatic Tanks Volume (L) Pressure (psi) Maximum hydraulic grade Steady state hydraulic grade Minimum hydraulic grade Pipe profile

80 Distance (m) Scenario 7 – Check/Control Valve Closes in 5 sec; 24” Surge Relief Valve Four 120,000 gal Hydro Pneumatic Tanks Volume (L)

Maximum transient pressure Steady state pressure Minimum transient pressure Water Vapor pressure Pressure (psi)

81 Distance (m) Scenario 7 – Check/Control Valve Closes in 5 sec; 24” Surge Relief Valve Four 120,000 gal Hydro Pneumatic Tanks Pressure (psi) ) hr Flow (m3/Flow

Time (sec)

82 Scenario 8 – Check/Control Valve Closes in 5 sec; 24” Surge Relief Valve Six 120,000 gal Hydro Pneumatic Tanks Volume (L) Pressure (psi)

Maximum hydraulic grade Steady state hydraulic grade Minimum hydraulic grade Pipe profile

83 Distance (m) Scenario 8 – Check/Control Valve Closes in 5 sec; 24” Surge Relief Valve Six 120,000 gal Hydro Pneumatic Tanks Volume (L)

Maximum transient pressure Steady state pressure Minimum transient pressure Water Vapor pressure Pressure (psi)

84 Distance (m) Scenario 8 – Check/Control Valve Closes in 5 sec; 24” Surge Relief Valve Six 120,000 gal Hydro Pneumatic Tanks Pressure (psi) ) hr Flow (m3/Flow

Time (sec)

85 Scenario 9 – Check/Control Valve Closes in 5 sec; 24” Surge Relief Valve Six 120,000 gal Hydro Pneumatic Tanks with 4” by-pass Volume (L) Pressure (psi) Maximum hydraulic grade Steady state hydraulic grade Minimum hydraulic grade Pipe profile

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

Maximum transient pressure Steady state pressure Minimum transient pressure Water Vapor pressure Pressure (psi)

87 Distance (m) Scenario 9 – Check/Control Valve Closes in 5 sec; 24” Surge Relief Valve Six 120,000 gal Hydro Pneumatic Tanks with 4” by-pass Pressure (psi) ) hr Flow (m3/Flow

Time (sec)

88 Scenario 13 – Check/Control Valve Closes in 5 sec; 24” Surge Relief Valve Five 120,000 gal Hydro Pneumatic Tanks with 4” by-pass Volume (L) Pressure (psi)

Maximum hydraulic grade Steady state hydraulic grade Minimum hydraulic grade Pipe profile

89 Distance (m) Scenario 13 – Check/Control Valve Closes in 5 sec; 24” Surge Relief Valve Five 120,000 gal Hydro Pneumatic Tanks with 4” by-pass Volume (L)

Maximum transient pressure Steady state pressure Minimum transient pressure Water Vapor pressure Pressure (psi)

90 Distance (m) Case Study 2

• 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

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

Volume Existing four 2-inch air valves only with pump check valve closing immediately ft ) Elevation(

92 Scenario A - Four 2-inch Air Valves Only with Pump Check Valve Closing Immediately ft ) Hydraulic Grade ( ) hr Flow (m3/Flow Air Vapor Volume (gal)

Time (sec)

93 Scenario B - Existing Four 4-inch Air Valves and 8-inch Surge Relief Valve Volume ft ) Elevation(

94 Scenario B - Existing Four 4-inch Air Valves and 8-inch Surge Relief Valve ft ) Hydraulic Grade ( ) hr Flow (m3/Flow Air Vapor Volume (gal)

Time (sec)

95 Scenario C inch Air Air Valves inch 5000gal AND Surge Tank with

Elevation (ft) Volume - Two 2 Two - 12” Inlet12” inch Air ValvesAir inch Fourand 4- 96 Scenario C - Two 2-inch Air Valves and Four 4- inch Air Valves AND 5000 gal Surge Tank with 12” Inlet ft ) Hydraulic Grade ( ) hr Flow (m3/Flow Air Vapor Volume (gal)

Time (sec)

97 Scenario C - Two 2-inch Air Valves and Four 4-inch Air Valves AND 5000 gal Surge Tank with 12” Inlet ft ) Hydraulic Grade ( ) hr Flow (m3/Flow Air Vapor Volume (gal)

Time (sec)

98 Surge Analysis Summary for Pressurized Pipes

99 Options for Surge Prevention • 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

100 Surge / Transient Pressure Modeling

• 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

101 Ask the Experts

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105 Presenter Biography Information

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.

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