factors controlling cathodic protection systems

8/3/2019 Factors Controlling Cathodic Protection Systems

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SACRIFICIAL ANODESACRIFICIAL ANODE

SYSTEMSYSTEM

C

A

T

H

O

D

E

A

N

OD

E

CURRENT

CURRENT

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IMPRESSED CURRENTIMPRESSED CURRENT

SYSTEMSYSTEM

CURRENT

C

A

TH

O

D

E

A

N

ODE

CURRENT

+-

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MINIMUM PROTECTION LEVELMINIMUM PROTECTION LEVEL

REFERANCE ELECTRODEREFERANCE ELECTRODE AEROBICAEROBIC ANAEROBICANAEROBIC

TYPETYPE ENVIRONMENT ENVIROMENTENVIRONMENT ENVIROMENT

1-COPPER/COPPER SULPHATE - 0.85 V1-COPPER/COPPER SULPHATE - 0.85 V -0.95 V-0.95 V

2-SILVER/SILVER CHLORID - 0.8 V2-SILVER/SILVER CHLORID - 0.8 V -0.9 V-0.9 V

3-ZINC3-ZINC + 0.25 V+ 0.25 V + 0.15 V+ 0.15 V

FRESH WATER & SOIL USE REFERANCE No. 1FRESH WATER & SOIL USE REFERANCE No. 1

FRESH & SEA WATER USE REFERANCE No. 2 or 3FRESH & SEA WATER USE REFERANCE No. 2 or 3

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MAXIMUM PROTECTION LEVELMAXIMUM PROTECTION LEVEL

MAXIMUM PROTECTION LEVEL IS LIMITEDMAXIMUM PROTECTION LEVEL IS LIMITED

BY COATING CATHODIC DISBONDINGBY COATING CATHODIC DISBONDING

LEVELLEVEL

Thin coating and or paintsThin coating and or paints - 1.0- 1.0 V maximumV maximum

Polymers (PVC, PE,etc )Polymers (PVC, PE,etc ) - 1.5 V maximum- 1.5 V maximum

Coal tar with fiber glassCoal tar with fiber glass - 2.5- 2.5 V maximumV maximum

Bituminized fiber glassBituminized fiber glass - 2.0 V maximum- 2.0 V maximum

Exceeding these limit more negatively will destroyExceeding

these limit more negatively will destroy

coating by disbondingcoating

by disbonding

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FACTORS AFFECTINGFACTORS AFFECTING

C / P SIZEC / P SIZE

SURFACE AREA,SURFACE AREA, more area=moremore area=morecurrentcurrent

CURRENT DENSITY FOR BARE METALCURRENT DENSITY FOR BARE METAL

LOWER RESISTIVETY NEEDS MORELOWER RESISTIVETY NEEDS MORECURRENTCURRENTCOATING QULITYCOATING QULITY ( high dielectric strength)( high dielectric strength)

Lower current leakageLower current leakage

ANEAROBIC BACTERIAANEAROBIC BACTERIA need more voltageneed more voltageRAIN&FLOODRAIN&FLOOD reduce soil resistivetyreduce soil resistivety

GROUND BED SOIL RESISTIVETYGROUND BED SOIL RESISTIVETY

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FIELD SURVEYFIELD SURVEY

* GEOGRAPHIC LOCATION OF SITE* GEOGRAPHIC LOCATION OF SITE

LONGTUDES/LATITUDES.LONGTUDES/LATITUDES.

* CLIMATIC CONDITION:* CLIMATIC CONDITION:

RAINY PERIOD,WAVE ACTIONS,DEPTH OF WATERRAINY PERIOD,WAVE ACTIONS,DEPTH OF WATER

WATER & SOIL RESISTIVETY ANAEROBICSWATER & SOIL RESISTIVETY ANAEROBICSBACTERIA &BACTERIA & pH VALUEpH VALUE

AVAILABILITY OF POWER SUPPLYAVAILABILITY OF POWER SUPPLYVOLTAGE,FREQUENCY & PHASEVOLTAGE,FREQUENCY & PHASE

* FORIENG STRUCTURES C/P OR NOT* FORIENG STRUCTURES C/P OR NOT

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STRUCTURE DESCRIPTIONSTRUCTURE DESCRIPTION

* ESTIMATE ALL SUBMERGED OR* ESTIMATE ALL SUBMERGED ORWETTED AREAS.WETTED AREAS.

* CONFIGURATION ANDLAYOUT:* CONFIGURATION ANDLAYOUT:

DIMENSIOS, & FOR PIPELINE: SIZE,DIMENSIOS, & FOR PIPELINE: SIZE,

MATERIAL,LENGTH,SIZE,PIPEWALLMATERIAL,LENGTH,SIZE,PIPEWALL

THICKNESSTHICKNESS..

** PROJECT LIFE TIMEPROJECT LIFE TIME

* NATURE AND TYPE OF COATING* NATURE AND TYPE OF COATING

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WHICH TYPE OF SYSTEM YOUWHICH TYPE OF SYSTEM YOU

CHOOSECHOOSE

DEPENDS ONDEPENDS ON

STRUCTURE SIZE & COPLEXITYSTRUCTURE SIZE & COPLEXITY ELECTROLYTE NATUREELECTROLYTE NATURE

ENVIRONMENTENVIRONMENT

POWER SUPPLY AVAILABILITYPOWER SUPPLY AVAILABILITY

PROXIMITY OF FORIGN STRUCTURESPROXIMITY OF FORIGN STRUCTURES

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SYSTEM SELECTION

Cases with soil resistivety less thanCases with soil resistivety less than(3000 Ohm.cm) both system are(3000 Ohm.cm) both system areusedused

Cases with higher resistivity valueCases with higher resistivity valueimpressed systems are optimumimpressed systems are optimum

Total project cost= the sum of:Total project cost= the sum of:Survey + engineering + supply + installationSurvey + engineering + supply + installation

+ 20 year operation costs+ 20 year operation costs

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SYSTEM SELECTION

51 2 3 46 7 8 9

10 1213 14 15 160

Years

Survey

InstallationengineeringEngineeringEngineering

Installation

suplay

supervision

Coastin$

TOTAL COSTS OVER 16 YEAR LIFE TIME

Fig. 3 IMPRESSED CURRENT SYSTEM

Maintenanc

e

PowerE

nergy

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SYSTEM SELECTION

51 2 3 4 6 7 8 9 10 12 13 14 15 160

Years

Survey

InstallationengineeringEngineeringEngineering

Installation

suplay

supervision

C

ostin$

TOTAL COSTS OVER 16 YEAR LIFE TIME

Fig. 2 SACRIFICIAL ANODE SYSTEM

Maintenance

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SYSTEM SELECTION

51 2 3 4 6 7 8 9 10 12 13 14 15 160

Years

MaintenanceC

ostin$

TOTAL C

OASTS

51 2 3 4 6 7 8 9 10 12 13 14 15 160

Years

TOTA

LCOA

STS

SACRIFI

CIALANO

DES

TOT AL COST COMPARISON

BETWEEN

IMPRESSED CURRENT & SACRIFICIAL SYSTEMS

IMPRESSED MOST ECONOMICAL SACRIFICIALMOST ECONOMICAL

IMPR

ESSE

DCUR

RENT

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Relation betweenRelation between

Coating and Cathodic ProtectionCoating and Cathodic Protection

100% 0.0%Coating Quality

0.0%CATHODIC PROTECTION

100%

OPTIMUM

COST

100% 100%

100%BARE

SURFACE

100%COATE

DSURFACE

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EFFECTSEFFECTS

WIND EFFECTWIND EFFECT

** INCREASE S CURRENT REQUIRMENTINCREASE S CURRENT REQUIRMENT* WIND GENERATORS NEED STABLE* WIND GENERATORS NEED STABLE

CONTINUOS AIR SPEED.CONTINUOS AIR SPEED.

CLOUDS EFFECTCLOUDS EFFECT

SOLAR RAYS GENERATS ELCTRICAL CURRENT BY THESOLAR RAYS GENERATS ELCTRICAL CURRENT BY THEUSE OF SOLAR FOTOVOLTAGE CELLS.CLOUDY DAYSUSE OF SOLAR FOTOVOLTAGE CELLS.CLOUDY DAYS

MINIMIZE OR PRIVENT POWER GENERATIONMINIMIZE OR PRIVENT POWER GENERATION

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GEUGRAFIC EFFECTGEUGRAFIC EFFECT

SOLAR POWERE OUTPUT ISSOLAR POWERE OUTPUT ISPROPORTIONAL WITH LIGHT INTESITY,PROPORTIONAL WITH LIGHT INTESITY,

MODULES SHOULD BE LOCATED FARMODULES SHOULD BE LOCATED FARAWAY FROM SHADOW.AWAY FROM SHADOW.

SOLAR PANEL INCLINATION ANGLESOLAR PANEL INCLINATION ANGLE

VARY FROM LOCATION TO ANOTHERVARY FROM LOCATION TO ANOTHER

LATITUDE & LONGTUDE OF THELATITUDE & LONGTUDE OF THESTATIONS DEFINE THE EXACT PANELSTATIONS DEFINE THE EXACT PANELTILT ANGLETILT ANGLE

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CASE STUDYCASE STUDY

EXAMPLEEXAMPLE

PROJECT DESCRIPTIONPROJECT DESCRIPTION

PROJECTPROJECT GAS PIPELINEGAS PIPELINE

LENGTHLENGTH 250 km250 km

DIAMETERDIAMETER 36 in36 in

COATINGCOATING 3 LAYER PE3 LAYER PE

TERRAINTERRAIN DESERT,ROCKY MOUNTAIN,DESERT,ROCKY MOUNTAIN,FLOOD DRAINS &MARCHESFLOOD DRAINS &MARCHES

SURFACE AREASURFACE AREA 718170 m2718170 m2

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SOIL RESISTIVETY SURVEYSOIL RESISTIVETY SURVEY

USING FOUR ELECTRODEUSING FOUR ELECTRODEMETHODMETHOD

SEVERELYAGRESSIVE

SEVERELYAGRISEV

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EFFECTEFFECT SOIL RESISTIVITYSOIL RESISTIVITY

SOILRESISTIVIT

K ohm. cm

DRY PERIOD RAINY PERIOD

Minimum 0.3 TO 0.4 0.2 TO 0.3

Maximum 20 5.0

C/P OUTPUT SHOULD COVER THE EFFECT SEASONALLYSOIL RESISTIVITY CHANGES (RAIN & FLOOD PERIOD)

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Design current densityDesign current density

Base average for bare steelBase average for bare steel 0.5 ma/m20.5 ma/m2

Average coating defectAverage coating defect 1.0 %1.0 %

Initial current densityInitial current density 0.005 ma/m20.005 ma/m2

Average current densityAverage current density 0.075 ma/m20.075 ma/m2

Final current densityFinal current density 0.15 ma/m20.15 ma/m2

Density increase by time ,coating ageingDensity increase by time ,coating ageing

Ref. to :DNV RP B401 (1993)Ref. to :DNV RP B401 (1993)

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Current RequirementCurrent Requirement

Current requirementCurrent requirementCurrent = Current density X AreaCurrent = Current density X AreaSo :So :

InitialInitial = 3.6 A= 3.6 A

AverageAverage = 54 A= 54 A

FinalFinal = 110 A= 110 A

MAX. current (final) should be used toMAX. current (final) should be used to

Cover the 20 year operationCover the 20 year operation

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CURRENT SPREADCURRENT SPREADCurrent spread is the length of pipeCurrent spread is the length of pipe

line section protected by one stationline section protected by one station

Drain point voltage max. -1500 mv

Min. protection level - 900 t0 - 850 mv

L L

2L

PROTECTED DISTANCE km

km km

Attenuation Curve

2 L = --------------------------8 * V

* D * I * R

WHERE :L = Distance in km v = Max. negative voltage shift in mV (300)D = Pipe diameter in m I = Leakage current density in micro AR = Pipe resistance in micro ohm/ m

Current Spread Equation

Drain point voltage operating -1200 mv

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Cathodic Protection StationsCathodic Protection Stations

How many CP Stations are needed ?How many CP Stations are needed ?

(pipe line length /spread length)(pipe line length /spread length)

250 km / 15.2km = 17 stations250 km / 15.2km = 17 stations

What is the station out put ?What is the station out put ?

(total current / number of stations)(total current / number of stations)110 A / 17 = 6.5 A110 A / 17 = 6.5 A

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GROUND BEDSGROUND BEDS

GROUND BEDS MUST ACHIEVE:GROUND BEDS MUST ACHIEVE:

Operate for the designed life periodOperate for the designed life period

Ground bed resistance less than 2.0Ground bed resistance less than 2.0ohmsohms

Anode current density, should not beAnode current density, should not be

exceededexceededSuitable anodic materialSuitable anodic material

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Material selectionMaterial selection Ferro silicon iron chromium is suitable forFerro silicon iron chromium is suitable for

R.O.W. soil conditionR.O.W. soil condition

Material capacityMaterial capacity0.5 kg/A/year without backfill0.5 kg/A/year without backfill

0.2 kg/A/year with backfill0.2 kg/A/year with backfill Total anodic material weight for 20 yearTotal anodic material weight for 20 year

Operation at 6.5 ampOperation at 6.5 amp

= 26 kg without backfill= 26 kg without backfill

= 2.6 kg with back fill= 2.6 kg with back fill

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NUMBER OF ANODES PERGROUND BEDTHNUMBER OF ANODES PERGROUND BEDTH

THE CALCULATED NUMBERS OF ANODESARE BASED ON LIFE TIMETHE CALCULATED NUMBERS OF ANODESARE BASED ON LIFE TIME

PERIOD ONLYPERIOD ONLY..

CHECK FOR G.B. RESISTANCE AND CURRENT DENSITYCHECK FOR G.B. RESISTANCE AND CURRENT DENSITY

Alternatives Size in inch weight Quantity

ALT I 1.5 X 60 13 5

ALT II 3 X 60 50 2

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MAXIMUM GB RESISTANCE = 2 ohmMAXIMUM GB RESISTANCE = 2 ohm Increasing anodes surface area reduceIncreasing anodes surface area reduce

total GB resistance.total GB resistance. 1.5 x 60 inch, 5 anode for lowering1.5 x 60 inch, 5 anode for lowering

resistanceresistance Checking the 2 ohm limit still high, anodeChecking the 2 ohm limit still high, anode

numbers should be increased 8 anode givenumbers should be increased 8 anode give

GB resistance = 1.2 ohmGB resistance = 1.2 ohm

It is advisable to increase anodes one byIt is advisable to increase anodes one byone to reach optimum economical solutionone to reach optimum economical solution

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Driving potentialDriving potential

Driving potential is the voltage capable toDriving potential is the voltage capable to

force the CP current through the system,force the CP current through the system,

which equal the sum of all system voltagewhich equal the sum of all system voltage

dropdropVoltage drop (v)= current (I)X resistance (R)Voltage drop (v)= current (I)X resistance (R)

V PipelineV Pipeline =6.5X0.25=6.5X0.25=1.6=1.6 VV

V cablesV cables =6.5X0.4=6.5X0.4 =2.6=2.6 VV

V ground bedV ground bed =6.5x1.3=6.5x1.3 =8.45 V=8.45 V

V electrolytic BEMFV electrolytic BEMF =2.0=2.0 VV

DRIVING POTENTIAL=totalDRIVING POTENTIAL=total =14.65 V=14.65 V

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CATHODIC PROTECTIONCATHODIC PROTECTION

STATION OUTPUTSTATION OUTPUTCALCULATION RESULTS:CALCULATION RESULTS: CURRENT REQUIRMENTCURRENT REQUIRMENT =6.5 A=6.5 A DRIVING POTENTIALDRIVING POTENTIAL =14.65 V=14.65 V

POWERPOWER =95.25 W=95.25 W STATION OUTPUT MUST COVER THESESTATION OUTPUT MUST COVER THESE

REQUIRMENTSREQUIRMENTS

STANDERED PRODUCTS SHOULD BESTANDERED PRODUCTS SHOULD BESELECTED WITH HIGHER RANGESELECTED WITH HIGHER RANGE

STATION OUTPUT = (20V,10A)STATION OUTPUT = (20V,10A)

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POWER SORCESPOWER SORCES

1-NATIONAL GRID1-NATIONAL GRID

2-OWEND DIESEL GENERATING SETS2-OWEND DIESEL GENERATING SETS

3-BY-PASS TURBINE GENERATORS3-BY-PASS TURBINE GENERATORS

4-THERMO GENERATING SETS4-THERMO GENERATING SETS5-WIND GENERATORS5-WIND GENERATORS

6-SOLAR POWER SYSTEMS6-SOLAR POWER SYSTEMS

ONE OF THE ABOVE ALTERNATIVESS WILLONE OF THE ABOVE ALTERNATIVESS WILLBE THE OPTIMUM CHOICEBE THE OPTIMUM CHOICE

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SOME OF THE ALTERNATIVES ARE OUT OFSOME OF THE ALTERNATIVES ARE OUT OFQUESTION FOR THE SMALL POWERQUESTION FOR THE SMALL POWER

REQUIRED, THOSE ARE:REQUIRED, THOSE ARE: THERMO GENERATORS AND BYPASS TURBINES.THERMO GENERATORS AND BYPASS TURBINES.

WIND GENERATORS CANNOT BE USED,AS WIND IS NOTWIND GENERATORS CANNOT BE USED,AS WIND IS NOTCONTINUES AND STABLE.CONTINUES AND STABLE.

THE RIMANING ALTERNATIVES CAN BETHE RIMANING ALTERNATIVES CAN BE

USED.USED.SOLAR-POWERED IMPRESSED CURRENT INSTALLATIONSSOLAR-POWERED IMPRESSED CURRENT INSTALLATIONSARE BECOMING INCREASINGLY COMPETITIVE IN MANYARE BECOMING INCREASINGLY COMPETITIVE IN MANYLOCATIONS,EVEN SO COST IMPACT SHOULD BE STUDIED.LOCATIONS,EVEN SO COST IMPACT SHOULD BE STUDIED.

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ALTERNATIVES COST ANALYSISALTERNATIVES COST ANALYSISINVOLVED COSTS ARE:INVOLVED COSTS ARE: ENGINEERINGENGINEERING SUPPLYSUPPLY INSTALLATIONINSTALLATION RUNNING EXCPENCES:RUNNING EXCPENCES: FUEL,OIL,SPARES,POWER,MAN POWER,etcFUEL,OIL,SPARES,POWER,MAN POWER,etc

TOTAL COASTS = THE SUM OF ALL ABOVETOTAL COASTS = THE SUM OF ALL ABOVECOSTS FOR THE PROJECT LIFE TIMECOSTS FOR THE PROJECT LIFE TIME

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POWER SORCESPOWER SORCES ALTERNATIVES COST ANALISISALTERNATIVES COST ANALISIS

COST ITEM NATIONALGRID DIESELGENERATOR SOLAR POWER

ENGINEERING &

SUPPLY

30 000 60 000 20 000

INSTALLATION &

HOUSING

10 000 10 000 10 000

FUEL+OIL+POWER 20 000 15 000 NA

SPARES+OVERALL

+MAINTENANCE

12 000 35 000 9 000

RELIABILITY MTBF 85 % 90 % 99 %

MTFR OUT OF COUNT 30 HOURS 12 HOURS

TOTAL 82 000 120 000 39 000

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CONCLUSIONCONCLUSION

FROM THE ABOVE DATA IT ISFROM THE ABOVE DATA IT ISCLEARLY OBVIOUS THAT USINGCLEARLY OBVIOUS THAT USING

SOLAR POWERD IMPRESSED SYSTEMSOLAR POWERD IMPRESSED SYSTEM

WITH 1.5X60 in ANODES IS THEWITH 1.5X60 in ANODES IS THESUCCESSFU CHOICESUCCESSFU CHOICE

OPTEMISATION AND COSTOPTEMISATION AND COSTANALYSIS HELP TACKING THE RIGHTANALYSIS HELP TACKING THE RIGHT

COST EFFECTIVE DECISIONCOST EFFECTIVE DECISION

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OPENOPEN

DISCUSSIONDISCUSSION

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SEE YOU NEXT YEARSEE YOU NEXT YEAR TECOFTECOF

THANK YOUTHANK YOU

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factors controlling cathodic protection systems

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