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Cathodic Protection for above ground storage tanks
HOCKWAYUNDERTANKBASE/EXTERNALANDINTERNALTANKPROTECTION
www.hockway.com
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UndertankCPSystems
Longer lasting Impressed ICCP systems
ImpressedcurrentCPICCPsystemsaremorereliable,
effectiveandflexiblethansacrificialanodesforundertank
baseprotection.
A typical CP Undertank system
ThematerialsrequiredforatypicalnewundertankICCP
systemwillinclude:
Astandardtransformerrectifier MMOtitaniumanodematerial
Permanentreferenceelectrodesformonitoring
Anundertanktubeforventilation,wateringand/orportablemeasuring
Transformer Rectifiers
OurrecommendedTRisourstandardoilcooledvariac
controlmodel.Howeverwecanproviderectifiersthat
matchtheoperatorsspecifications.Typically,oilcooled
isfortheextreme(hot,cold,dusty)environments.
Air-cooledformilderclimatesorair-conditionedshelters.
ForhazardousareaswesupplyATEXratedTRs.
Hockwaycanalsocutcostsbydesigningcathodic
protectionsystemswithdualchanneltransformer
rectifierstoprotecteitherinternalandexternalimpressed
CPsystemsor2xCPexternaltanksystemssimultaneously.
Undertankbase/externalandinternaltankprotection.
Hockwaycansupplycorrosionprotectionforanytankdesignedtooperatorandinternationalspecificationsandstandards,whethernewbuildorexistingretrofit.Wecateroursolutionstowardstankdimensions,product,coatingtypeandquality,andoperatingtemperature.
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Anodes
FornewbuildtankswithICCPwerecommendMMO(Mixed
MetalOxide)titaniumAnodes.Thesecanbelaidusinga
piggybacklooporlineargridarray500mmbelowthe
tankbasetoprovidecloseanodedistributionsystem.
Werecommendloopanodelayoutsystemsdueto
thesignificantbenefitstheyoffer.Theadvantages
aretheeaseandflexibilityininstallationandlater
commissioning,andmonitoringwithgreaterlong
termreliability.
Anode Junction Box
Wesupplyanodejunctionboxesthatcandoubleup
asamonitoringboxwherethereferenceelectrodes
andmonitoringcablearealsoterminatedandthereby
reducingcosts.
Reference Electrodes to monitor CP performance
WerecommendCopperCopperSulphateandZincreference
electrodesareinstalledformonitoringpurposes.
R6
R3
R11
23
45
6
0
R2
R7
R5
REFERENCE CELLS
ANODE JUNCTION BOX
POSITIVE FEEDER CABLE
DRAW OFF SUMP
ANODE LOOPS
TRANSFORMER RECTIFIER
UNDERTANK
ANODE JUNCTION
REFERENCE ELECTRODES
200
350
750
SAND
HDPE MEMBRANE WELL BRADED COMPACTED SANDUPVC SLEEVES THROUGH
TANK BASE POSITION
ANODES LOOPS
Fig 2: Typical Undertank loop layout
Fig 1: Typical Undertank side view layout using the loop system
Example of Grid System
Example of Loop System
This image is courtesy of Ceranode
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www.hockway.com
Choosing the external tank CP system New or retrofit
Options Advantages Disadvantages
Sacrificial Lowcost
Limitedeffect,noincreaseofoutputcapability,failprematurely
Impressed Reliable,canincreaseoutput, Highercostthansacrificial
longlasting Moredifficult
Grid/ribbon Lessexpensivethanlinear,
Difficulttoinstall,reliantongood moreanodematerial
connectionsinthefield,sumps problematicwithcontacttoanodes
Loop/wire Nomessyinfieldconnections Moreexpensivethangridanodes,
required,readytoinstall(outof lessanodematerial
theboxstraightintheground),reducesconstructiontime,sumpscanbeavoidedduringconstruction
SilverSilverChloride Abilitytomeasurepotentials
Mixedreliability,subjecttodrying, ReferenceElectrodes underthetank
moreexpensive
CopperCopperSulphate Reliableincleansand Subjecttodrying
ReferenceElectrodes
ZincReferenceElectrodes Goodtocompareagainstother
Notsuitableasstand otherPermanentReference alonereference
ElectrodetypesR
efer
ence
Ele
ctro
des
Syst
emA
nod
e La
yout
Undernormalcircumstanceswithgiveninformationscope,HockwaysrecommendedsystemisanMMOtitanium,
looparrangementwithastandardvariaccontrolledTRandpermanentCopperCopperSulphatereferenceelectrodesfor
potentialmonitoring.Aventilation/portablemonitoring/wateringpipeisalsorecommended.
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Tank Type System Type Information Typical system
Sacrificial Smalldiametertanks,
Aluminium,Magnesiumorzincanodes
TemperatureAmbient,
Midrangeresistivity
ICCP Largediametertanks SiFeorMMOTitanium
Lowresistivityrequireslargecurrent Tubes,MMO/Platinised
Highresistivityrequireshighervoltage NiobiumTitaniumanodes
Hightemperatures orCopperwire
TRdrivenusingautopotentialcontrol
Sacrificial
Generallynotusedasproductsandoperatingconditionscanbe
particularlyaggressive
ICCPCathodic Highcurrentrequirement
Easiertocontrol
ICCPAnodic
Suitableforlowphandhightemperature,lowerpowerrequirements,potential
monitoringcritical,hardtocontrol,variedsuccess
Sacrificial Usedforwaterdropout
Magnesiumorzincanodeslocatedon
tankfloor
Nomonitoringdevicesemployed.
www.hockway.com
ANODE COFFER DAM
ANODE JUNCTION BOX
REF
EREN
CE E
LECT
RO
DE
CAB
LE&
SU
PPO
RT
RO
PE
1.5M
M M
MO
AN
OD
E W
IRE
& S
UPP
OR
T R
OP
E
DIAGRAM 3a
TANK SHELL
CABLE TRAY
TR
TS
TANK
POLYPROPYLENETENSIONING ROPE
HHLL
ELECTRODE COFFER DAM
ANODE HEADER CABLE SPLICE
Fig 3a: Typical Internal Tank ICCP System
DIAGRAM 3b
ANODE COFFERDAM ASSEMBLY
TO THE JUNCTION BOX
TANK ROOF
ANODE WIRE HEADER CABLE
ANODE WIRE TO HEADER CABLE SPLICE
MMO ANODE WIRE
6 DIA PIPEFLANGE ASSEMBLY
ANODE WIRE CABLE TIEDTO ROPE AT INTERVALS
0.6MM POLYPROPYLENESUPPORT ROPE
NYLON THIMBLE
POLYPROPYLENE TENSIONING ROPE
TETHERING LUG TANK FLOOR
Fig 3b: Anode Cofferdam Assembly
Choosing Tank Internal Protection
AlthoughwatervariesinresistivityHockwaysrecommendedmethodisusinganimpressedcloseanodewiresystem.
Water Carrier
Chemical
Oily Product
Storage Tanks
InternalTankCPSystems
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A Typical Impressed CP Internal System
Atypicalinternaltankprotectionpackagewould
incorporateatransformerrectifier,MMOtitaniumanode
materialandsilver/silverchloridereferenceelectrodes.
Equipment and Materials Transformer Rectifier
Asthetankcontentschange,sodothecurrent
requirements.Topreventunderoroverprotection,we
supplyautopotentialcontrolledtransformerrectifierunits.
TosaveoncostHockwayareabletoprovidea2
channelTRtoprotectbothtankinternalandexternal.
Anodes
WerecommendMMOTitaniumorPlatinisedNiobium
wireanodesespeciallyatthehighresistivities,to
ensureconsistancyanduniformprotection.Forlower
resistivitiestubesofsiliconironorMMO/platinised
titaniumanodescanbesuspendedinthewater.
Reference Electrodes
SilverSilverChloridereferenceelectrodesarerequired
especiallyifanautopotentialcontrolledTRisemployed.
ThereferencepotentialfeedsbacktotheTRtovarythe
outputdependingonproductlevels.
Sacrificial Systems
Wesupplyaluminium,magnesiumandzincanodestobe
distributeduniformlyaroundthetankfloorandtanksides.
Hydrocarbonproductsstoragetankssometimescontain
residueofwater,frequentlysalineinnature,thatfallsout
andcollectsatthebaseofthestoragetank.Toprevent
corrosionsacrificialanodesshouldbeinstalledalongthe
tankfloor.
Special Cases
Storagetankscanholdproductsthatarevery
acidicoralkalineinnature.Duetothesevariations
eachsystemisdesignedonacase-by-casebasis.
ANODE FIXING AT TANK BASE (SIDE ELEVATION)ANODE FIXING AT TANK
BASE (SIDE ELEVATION)
ANODE FIXING AT TANK BASE (SIDE ELEVATION)
INTERNAL TANK SACRIFICIAL ANODE ARRANGEMENT
Fig 4: Internal Tank Sacrificial Anode Arrangement
Hockway UK Head
OfficeTrowersWayCentre,Holmethorpe,IndustrialEstate
Redhill,SurreyRH12LP,UnitedKingdom
Tel:
+44(0)1737762222Fax:+44(0)1737236100Email:[email protected]
Contact
Hockway Aberdeen7QueensGardens,AberdeenAB154YD
UnitedKingdom
Tel:
+44(0)1224443523Fax:+44(0)1224626227Email:[email protected]
Hockway ItalyC.soMartiridellaLiberta,17
15076OVADAALITALIA
Tel:
+39(0)14381444Fax:+39(0)14381444Email:[email protected]
Hockway UAEP.O.Box10559,RasAlKhaimah
UnitedArabEmirates
Tel:
+971(0)72444923Fax:+971(0)72444932Email:[email protected]
