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STORAGE TANKSSTORAGE TANKSCATHODIC PROTECTIONCATHODIC PROTECTION
PREPERED AND PRESENTEDPREPERED AND PRESENTED
BYBY
M.Y.EL SHAZLYM.Y.EL SHAZLY
TECOTECOFF
SACRIFICIAL ANODE SYSTEMSACRIFICIAL ANODE SYSTEMTECOTECOFF
CATHODE
ANODE
CURRENT
CURRENT
IMPRESSED CURRENTIMPRESSED CURRENTSYSTEMSYSTEM
TECOTECOFF
CATHODE
ANODE
CURRENT
+-
CURRENT
INTERNAL & EXTERNALPROTECTED AREA
INTERNALPROTECTION
EXTERNALPROTECTION
INTERNALPROTECTION
INTERNALPROTECTION
EXTERNAL PROTECTION
INTERNAL PROTECTION
PROTECTED AREA = AREA CONTACTING ELECTROLYTE (SOIL AND OR CONDUCTIVE LIQUID)
TECOTECOFF
TANK INTERNAL CATHODIC TANK INTERNAL CATHODIC PROTECTIONPROTECTION
IMPRESSED CURRENT SYSTEMIMPRESSED CURRENT SYSTEM
h 2
h1
Referenceelectrode
AnodeTransformer rectifierautomatic control
AV
000
DC outputvolt/current
Set point
Ref. protectionlevel
Protected area = bottom area + shell wetted area
shell wetted area = II x tank diameter x height
bottom area II x (tank diameter) 2 4
Protection current = protected area x current intencity
TECOF
TANK INTERNAL CATHODIC TANK INTERNAL CATHODIC PROTECTIONPROTECTION
SACRIFICIAL ANODE SYSTEMSACRIFICIAL ANODE SYSTEM
h 2
h1Anode
Protected area = bottom area + shell wetted area
shell wetted area = II x tank diameter x height
bottom area II x (tank diameter) 2 4
Protection current = protected area x current intencity
Welded anodes
Suspendedanodes
TECOF
STORAGE TANKS EXTERNAL STORAGE TANKS EXTERNAL CATHODIC PROTECTIONCATHODIC PROTECTION
UNDER BASE ANODE INSTALLATIONUNDER BASE ANODE INSTALLATION
RODE ANODE TYPERODE ANODE TYPE
50 cm
-950 mv
-850 mv
Rod anodes
TECOF
STORAGE TANKS EXTERNAL STORAGE TANKS EXTERNAL CATHODIC PROTECTIONCATHODIC PROTECTION
•UNDER BASE ANODE TYPEUNDER BASE ANODE TYPE
• INSTALLATIONINSTALLATION
50 cm
-900 mv
-850 mv
RIBBON ANODE
TECOF
STORAGE TANKS EXTERNAL STORAGE TANKS EXTERNAL CATHODIC PROTECTIONCATHODIC PROTECTION
•DISTREBUTED ANODE INESTALLATIONDISTREBUTED ANODE INESTALLATION
5 -10 m
5 -1
0 m
Rod anodevertical or horizontal
-850 mv
-850 mv
Min. potential point
TECOFRIM POTENTIAL = 1100 TO 1200 BS STANDERED
OR
ADD 1mv per one foot of tank diameter to the min. protection level (-850 mv)
STORAGE TANKS EXTERNAL STORAGE TANKS EXTERNAL CATHODIC PROTECTIONCATHODIC PROTECTION
Deep well groundbed
Tank-1 Tank-2 Tank-3 Tank-4
Tank4
Tank Farm
Tank3
Tank2
Tank7
Tank7
Tank6
Tank5
Tank1
Deep wellGB
DEEP WELL GROUND BED DEEP WELL GROUND BED INESTALLATIONINESTALLATION
TECOF
STORAGE TANKS EXTERNAL STORAGE TANKS EXTERNAL CATHODIC PROTECTIONCATHODIC PROTECTION
REMOTE GROUND BED INESTALLATIONREMOTE GROUND BED INESTALLATION
TECOF
Tank3
Tank2
Tank1
Tank6
Tank5
Tank4
Tank9
Tank8
Tank7 REMOTE GB
TANK FARM
-450 mv
-850 mv
-2500 mv
Remote GB
CURRENT REQUIREMENTCURRENT REQUIREMENT
11 - - SURFACE AREA TO BE SURFACE AREA TO BE PROTECTEDPROTECTED
•EXTERNAL = BOTTOM AREA (BARE)EXTERNAL = BOTTOM AREA (BARE)
INTERNAL = BASE AREA + WETTED SHELL AREA INTERNAL = BASE AREA + WETTED SHELL AREA (BARE)(BARE)
IF COATED A COATING DEFFECT PERCENTAGE MUST BE APPLAYEDIF COATED A COATING DEFFECT PERCENTAGE MUST BE APPLAYEDTECOF
CURRENT REQUIREMENTCURRENT REQUIREMENT
22 – – CURRENT INTENSITYCURRENT INTENSITY
INTERNALINTERNAL::
FRESH WATER = 20 ma/m2FRESH WATER = 20 ma/m2
SALT WATER = 100 ma/m2SALT WATER = 100 ma/m2
EXTERNALEXTERNAL::
DEPEND ON SOIL RESISTIVITYDEPEND ON SOIL RESISTIVITY
RANGES FROM 5 TO 0.5 ma/m2RANGES FROM 5 TO 0.5 ma/m2TECOF
CURRENT REQUIREMENTCURRENT REQUIREMENT
33 – – CURRENT CALCULATIONCURRENT CALCULATION= = SURFACE AREA TO BE PROTECTED X CURRENT SURFACE AREA TO BE PROTECTED X CURRENT INTENCITYINTENCITY
11 - -COATING DEFFECT PERCENTAGE TO BE TAKEN INTO COATING DEFFECT PERCENTAGE TO BE TAKEN INTO CONSEDIRATIONCONSEDIRATION
22 - -IF THE TANK IS USED TO STORE WATER, THIS MEENSIF THE TANK IS USED TO STORE WATER, THIS MEENS
THAT SHELL WETTED AREA WILL CHANGE WITH THAT SHELL WETTED AREA WILL CHANGE WITH HIGHT, . HEIGHER CURRENT VALUE MUST BE HIGHT, . HEIGHER CURRENT VALUE MUST BE TAKEN IN SIZINGTAKEN IN SIZING
TECOF
ELECTRICAL EQUIVALENT ELECTRICAL EQUIVALENT CIRCUITCIRCUIT
R2 R1
R3 R4
VOUTPUT
CURRENT
CURRENT = VOLTAGE DIVIDED BY RESISTANCEOHMS LOW
EQUIVALENT CIRCUIT RESISTANCE = R1+R2+R3+R4WHERE:
R1 = NEGATIVE CABLE RESISTANCE ohmR2 = TANK STEEL RESISTANCE ohmR3 = GROUND BED RESISTANCE ohmR4 = POSITIVE CABLE RESISTANCE ohm
CURRENT = PROTECTION CURRENT DEMAND in ampereVOLTAGE = DRIVING POTENTIAL in volt
TECOF
SAMPLES OF TANK SAMPLES OF TANK CORROSION CELLSCORROSION CELLS
+
-
+-
+ --
OLD METAL
NEW METAL
OLD METAL
+-
BATCH CORROSIONWELD CORROSION
CP current
Tank bottom
Concrete ringbeam
RING BEAM CORROSION
CORROSIONAREA
DEBARY
CORROSIONPRODUCTS
5 deg.
Bottom plates
ANNUAL PLAT WELD CORROSION
