BAC 31213C - Chemical Treatment Requirements; Passivation

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• ToavoidbiologicalcontaminationandminimizetheriskofLegionella,initiatethe
biocidetreatmentprogramatstart-upandcontinueonaregularbasisthereafterin
accordancewiththetreatmentsupplier’sinstructions.
• Bleed/blowdownorchemicaltreatmentusedforcorrosionandscalecontrolaloneis
notadequateforcontrolofbiologicalcontamination.
• Introducesolidorgranularbiocidesthroughachemical“pot”feederinstalledin
parallelwiththesystemcirculatingpump.Dilutedliquidbiocidesmaybeadded
directlytothecoldwaterbasin.
• Ifozonewatertreatmentisused,atnopointshouldconcentrationsexceed0.5ppmto
avoidcorrosion.
Chemical Treatment Requirements
Chemicaltreatmentprogramsmustmeetthefollowingrequirements:
• Thechemicalsmustbecompatiblewiththeunitmaterialsofconstructionaswellas
othermaterialsusedinthesystem(pipe,heatexchanger,etc.).
• Chemicalscaleandcorrosioninhibitors,particularlyacid(ifused),shouldbe
introducedintothecirculatingwaterthroughautomaticfeeders.Thisshouldbedone
atapointinthesystemwheretotalmixinganddilutionoccurbeforereachingthe
evaporativecoolingequipment.Thepreferredinjectionpointforchemicalscaleand
corrosioninhibitorsisonthedischargesideofthesystemcirculatingpump(s).These
chemicalsshouldnotbebatch-feddirectlyintotheunit’scoldwaterbasinorwater
distributionsystem,asthiscanseverelydamageareasdirectlycontacted.
• Whenchlorineisaddedtothesystem,freeresidualchlorineshouldnotexceed1ppm,
exceptduringstart-upifbiologicalshocktreatmentisutilizedduringtreatment.Refer
to“Start-Up”onpage 5forlimits.Exceedingthislimitmayacceleratecorrosion.
Passivation
• Passivationistheformationofaprotective,passive,carbonatelayerongalvanized
steelsurfaces.
• Toprovidemaximumprotectionfromcorrosiononnewlyinstalledunitstakespecial
measurestopassivategalvanizedsteelsurfaces.
• Toensureproperpassivationofthegalvanizedsteel,keepthepHofthecirculating
waterbetween7.0to8.2forfourtoeightweeksafterstart-up,oruntilnewzinc
surfacesturndullgrayincolor.
• IfwhiterustformsongalvanizedsteelsurfacesafterthepHisreturnedtonormal
servicelevels,itmaybenecessarytorepeatthepassivationprocess.
NOTE: Stainless steel cold water
basins and basins protected by
the TriArmor
®
Corrosion Protection
System or thermosetting hybrid
polymer do not require passivation.
However, if the upper structure is
galvanized steel, passivation is
required on the galvanized area.