Surge Analyses

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Transient Flow in Pipe SystemsTransient Flow in Pipe Systems

THEORETICAL OVERVIEWTHEORETICAL OVERVIEWOF SURGE ANALYSESOF SURGE ANALYSES

November 2004

University of Pretoria

Prof SJ van Vuuren

Tel: +27 012 420 2438

Website:

http://www.up.ac.za/academic/civil/divisions/water.html

Layout of PresentationLayout of Presentation

Introduction

Basic theory of transient flows Rigid Column Theory

Elastic Theory

Influence of pipeline support on wave celerity

Propagation of transient waves

Theory for non-instantaneous disturbances

Calculation of transient pressures

Causes of transient flows

Fluid transient risk assessment procedure(TRAP)

Surge protection options

Computer-aided transient analysis


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IntroductionIntroduction

What is surge?Variation in pressures that are generated by a

change in the operational status

How are surge waves created?Foreseen operational changes

Unforeseen operational changes

Layout changes

Basic theory of transient flowBasic theory of transient flow

RIGID COLUMN THEORY

dt

dv

g

LH =

ELASTIC THEORY (RIGID PIPE)

0cVP =

)/(

)/(

)/(

)/(

0

3

2

smvelocityflowV

mkgwaterofmassunit

smpiperigidaforceleritywaveC

mNnfluctuatiopressureP

=

=

=

=

Where:


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ELASTIC THEORY (RIGID PIPE) (Continued)

+

=

tD

EK

cc

1

1'

Where:

)(

)(

)/(

)/(mod

)/('

*2

*2

mpipeofthicknesswallt

mpipeofdiameterD

mmNmaterialpipeofelasticityE

mmNwaterofulusbulkK

smpipeelasticanforceleritywavec

=

=

=

=

=

*Values of K and E are shown in Annexure 1


SUPPORT OF THE PIPELINE

PROPAGATION OF TRANSIENT WAVES

Case 1: Anchored at upstream end

21=C

Case 2: Anchored throughout against longitudinal movement

2

1 1 =C


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Transient flow theory for nonTransient flow theory for non--

REQUIREMENTS

elasticity effect of losses

non-instantaneous valve movement

PARTIAL DIFFERENTIAL FORMULAE

instantaneous disturbancesinstantaneous disturbances

0sin2

=

+

++

x

u

g

c

t

Hu

x

Hu

02

=++

dt

du

D

uuHg

Visualizing the movementVisualizing the movement


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Surgemov1.mov

Surgemov2.mov


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Pump trip

Formation of vapor cavity

Growth of vapor cavity

Flow reversal

Steady state

Collapse of vapor cavity Bang

Calculation of transientCalculation of transient

arithmetic

graphic

characteristics algebraic

implicit

linear

wave-plan

other

pressurespressures


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Causes of transient flowsCauses of transient flows

Pump start-up

Pump trip

Variation in demand

Unintentional changes in operationalposition of control valves

Fluid Transient RiskFluid Transient Risk

Checklist of fault conditions

TRAP

Assessment Procedure (TRAP)Assessment Procedure (TRAP)


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The route of the pipeline is changed?

The demand on the system is increased?

The basic design data is unreliable by x % (e.g. heads,

flows, component operating characteristics, materials

specifications, fluid properties and quality, etc.)?

Changes are made to the system design?

Assessment Procedure (TRAP)Assessment Procedure (TRAP)Checklist of fault conditions

Design/Installation


The power fails to the motors driving the pumps?

The pump delivery valve is closed in t seconds?

One pump trips but others keep running?

An operator opens/shuts valve y too quickly?

The demand on the system is increased?


Normal operation


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A pump is re-started within t seconds of being tripped?

A control or emergency shut-down valve is shut rapidly?

An operator opens/shuts valve y too quickly?


Hazardous operation


Component x malfunctions (e.g. an automatic control

valve, pressure relief valve, vacuum breaker, etc.)?

The surge suppression strategy/control devices

malfunction?


System malfunction


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Fluid Transient RiskFluid Transient RiskAssessment Procedure (TRAP)Assessment Procedure (TRAP)

Successful

implementation

Devise test program for commissioningtest program for commissioning

procedures

10

Ensure long term

efficiency

Finalize the design, and prepare operationaloperational

constraints and guidelinesconstraints and guidelines in accordance

with the validated control and suppression

strategy

9

Optimal surge analysisPrepare specifications for detailed computerspecifications for detailed computer

analysisanalysis

Refine the control measures

8

ObjectiveDescriptionAction

Surge protection optionsSurge protection options

Pump start-up

Pump trip


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Surge tank Air valve Reflux valve

Surge protection optionsSurge protection optionsWhere is the transient

event initiated?

Upstream end An intermediate point Downstream end

Pressure

rises first

Pressure

drops first

Pressure

rises first

Pressure

drops first

Air vessel /

accumulator

Check valve

Relief

system

Surge shaft

Could secondary devices elsewhere in the system be of benefit ?

e.g. Air valves, Feed tanks, surge shafts, etc.

Air vessel /

accumulator

By-pass

Check valve

Vacuum

breaker

Air vessel /

accumulator

Relief

system

Surge shaft

Air vessel /

accumulator

Feed tank

Surge shaft

Vacuum

breaker

Can a By-

pass device

help ?

No No

Select and/or Design

Yes

Select and/or Design


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Summary of Water Hammer Protection

Normally used in conjunction

with some other method of

protection. Water column

separation possible

In-line reflux valve

Pipeline profile should be

convex downwards. Watercolumn separation likely

Automatic release valve

Some water may also be

drawn through the pump

Pump bypass reflux valve

Approximate onlyInertia of pump

RemarksRequired range of

variables

Method of protection (in

approximate order of

increasing cost)

01.02

0

2

>wALH

MN

10

0 >>gH

cV

10 >gh

cV

10

0


Summary of Water Hammer Protection


near hydraulic grade line to

limit the height of tank

(practical)

Limited heightSurge tanks

H = pressure head at tank,


convex upwardsDischarge tanks

Pipeline profile preferably

convex downwards

Air vessel

RemarksRequired range of

variables

Method of protection (in

approximate order of

increasing cost)

10 >gh

cV

10

0

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