factors controlling cathodic protection systems
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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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ENVIRONMENTENVIRONMENT
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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ENVIRONMENTENVIRONMENT
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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GROUND BEDSGROUND BEDS
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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GROUND BEDSGROUND BEDS
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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GROUND BEDSGROUND BEDS
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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POWER SORCESPOWER SORCES
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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POWER SORCESPOWER SORCES
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
TECOFTECOF
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