Cathodic Protection for Above Ground Storage Tanks (1)

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  • Cathodic Protection for above ground storage tanks

    HOCKWAYUNDERTANKBASE/EXTERNALANDINTERNALTANKPROTECTION www.hockway.com

  • 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.

  • 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

  • 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.

  • 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

  • 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:enquiries@hockway.com

    Contact

    Hockway Aberdeen7QueensGardens,AberdeenAB154YD

    UnitedKingdom

    Tel: +44(0)1224443523Fax:+44(0)1224626227Email:enquiries@hockway.com

    Hockway ItalyC.soMartiridellaLiberta,17

    15076OVADAALITALIA

    Tel: +39(0)14381444Fax:+39(0)14381444Email:ecampedelli@hockway.com

    Hockway UAEP.O.Box10559,RasAlKhaimah

    UnitedArabEmirates

    Tel: +971(0)72444923Fax:+971(0)72444932Email:sales@hockway.com

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