BAC 31213C - Corrosion and Scale Control; Biological Control

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• Corrosion–Redrustonsteelcomponentsandwhiterustongalvanizedsurfacesmay
affectthelongevityofsystemcomponents.
• Scale Formation–Scalenotonlyreducesheattransferandsystemefciency,but
alsomayleadtounderdepositcorrosion.Ifscaleisnotcontrolled,itmaycontinue
buildingoncriticalcomponentssuchasthellandseverelyimpactthermal
performance.
• Biological Fouling
–Slimeandalgaeformationsmayreduceheattransfer,promote
corrosion,andharborpathogenssuchasLegionella.
Corrosion and Scale Control
• Tocontrolcorrosionandscale,maintainthewaterchemistryoftherecirculating
waterwithintheparameterslistedinTable 5.Thespecicmeasuresrequiredvary
fromsystemtosystemandaredependentonthechemistryofthemake-upwater,the
metallurgyofthepipingandheattransferdevicesexposedtotherecirculatingwater,
andthetemperaturesatwhichthesystemwillbeoperating.
• Bleed/blowdown,thecontinuousowofasmallportionoftherecirculatingwaterto
adrain,isusedtocontroltheconcentrationofdissolvedsolids.Onrareoccasions,
thismaybeadequatetocontrolscaleandcorrosion.Moreoften,chemicalscaleand
corrosioninhibitorsarenecessary,whichraisetheallowablelevelofdissolvedsolids
withouttheriskofscaleandcorrosion.
• Incaseswherebleed/blowdownaloneisbeingemployedforcorrosionandscale
controlwithoutchemicaltreatmentyourwatertreatmentspecialistmayrecommend
moreconservativelimitsthanthoseshowninTable 5.
NOTES:
1. Galvanized steel units require
passivation in order to prevent
white rust (refer to “Passivation”
on page 24).
2. Hardness and alkalinity limits
may be exceeded under certain
circumstances. Consult your
water treatment specialist for
recommendations.
3. The conversion factor used to
determine conductivity is 0.625
(TDS = 0.625 x Conductivity).
Biological Control
• Thewarm,oxygenandnutrientrichenvironmentinsideevaporativecoolingequipment
providesanidealenvironmentforthegrowthofalgae,slime,andothermicro-
organisms.Uncontrolled,thiscanreduceheattransfer,promotecorrosion,and
promotethegrowthofpotentiallyharmfulorganismssuchasLegionella.
Table 5. Quality Guidelines for Circulating Water
Property of Water Recommended Level
pH 6.5 to 9.0
[1]
Hardness as CaCO
3
30 to 750 ppm
[2]
Alkalinity as CaCO
3
500 ppm maximum
[2]
Total Dissolved Solids (TDS) 1500 ppm maximum
Conductivity 2400 micromhos
[3]
Chlorides
250 ppm maximum Cl
(410 ppm maximum as NaCl)
Sulfates 250 ppm maximum
Silica 150 ppm maximum
Corrosion Protection
Water Treatment
Corrosion and Scale Control
Biological Control