Keith Allen, P.E ., BCEE

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Keith Allen, P.E ., BCEE




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Slide1

Keith Allen, P.E., BCEEAWWA TrainingMay 17, 2016

Corrosion

Control

Slide2

Vulnerable GroupsWhile most regulated contaminants are harmful to some degree, many are chronic and do not have immediate effects except on vulnerable groups such as:

Children (low body weight, high metabolism)

Elderly

PregnantAlready ill (immune system, medication)Immune compromisedAllergies Specific diseases (Wilson disease – Copper)

Slide3

Corrosion Control Particulate matter Most corrosion products are not dissolvedThey are dislodged by hydraulic action or scour (high velocity)

While detention time will increase dissolved products, it has little effect on the major component of metal content in lead and copper samples

Corrosion material from lead pipe, lead solder joints, and brass fittings can be between 60% and 95% particulate

Generally, corrosive water leads to increased particulate matter Bio-availabilityParticulate matter does not contribute to metal availability for body function unless it can be dissolved by stomach acid in three hoursEPA sample procedure requires 16 hours detention in mild acid to simulate the bioavailability component

Slide4

Corrosion Control Current Issue with Particulate matter (2007 AWWA)Study using Simulated Gastric Fluid (SGF) determined that particulate matter from red and yellow brass fittings is much more likely to dissolve (become bio-available)Lead pipe, brass fittings, and lead solder joints contribute more than 60% leaded particulate matter New brass fittings contribute up to 95% leaded particulate matter. Smaller particles contribute a higher bio-available fraction (mining studies)

Particle lead concentration > 65% contributes a higher bio-available fraction (mining studies with SGF)

Particle Zinc concentration > 20% contributes a higher bio-available fraction (mining studies with SGF)

Particles from brass are majority copper but usually contain zinc

Slide5

Corrosion Control Do EPA sampling and analysis methods capture all lead? In general, current EPA analysis will vastly overestimate bio-availability of particulate lead except that from brassLead-tin solder joints (from chart results AWWA 2007)About 5% of particulate lead converted by EPA method is bioavailableAbout 1% of total particulate

lead

is bioavailable

EPA method only captures 20% of the total particulate leadLead pipe (pure lead particles) (from chart results AWWA 2007)About 60% of particulate lead converted by EPA method is bioavailableAbout 5% of total particulate lead is bioavailableEPA method only captures 10% of the total particulate leadBrass fittings (from chart results AWWA 2007) About 95% of particulate lead converted by EPA method is bioavailableAbout 80% of total particulate lead is bioavailableEPA

method captures 85%

of the total particulate lead

Slide6

Corrosion Control Is particulate lead that is not bioavailable a problem?All samples exceeding action level are captured by EPA procedureHigher lead levels mean more error in capturing total lead

Since physical action is more important than detention time, should sampling procedures be site specific

Optimum corrosion control can significantly reduce particulate matter

What changes may be needed?Ban lead in brass fitting – 2013Change sampling procedures to better capture particulate matter?Change flushing instruction to be site specific?Change out everybody’s plumbing?

Slide7

Corrosion Control In water, dissolved substances separate into ionsIons are electrically charged particlesPositive (+)Negative (-)Ex: Salt dissolves in water into sodium (Na+) and chlorine (Cl-) Compounds formed by ions

Lime (calcium oxide -

CaO

)Soda Ash (sodium carbonate - Na2CO3)Baking Soda (sodium bicarbonate - Na2(HCO3)2)

Slide8

Corrosion Control pH or Hydrogen ion concentrationPure water doesn’t exist in naturepH ranges extends 0 to 14Values less than 7.0 are acidicValues greater than 7.0 are basicShallow ground water may have low pH

Water with low pH tends to be corrosive due to high CO2

Measuring pH

Electrodes (pH meter)Color matching equipment

Slide9

Corrosion Control Water alkalinitysubstances in water which neutralize acidAn increase, lowers acidity and raises pHInfluences water corrosiveness Alkalinity is added when water contacts surrounding rocks and soilHydroxyl (OH-)

Carbonate (CO

3

2-)Bicarbonate (HCO3-)At low pH, alkalinity in the form of H2CO3 (Carbonic Acid)

Slide10

Corrosion Control Chemicals lowering pHChlorineAlumSulfuric Acid

Hydrofluosilicic

Acid

Carbon DioxideCarbonic AcidChemicals raising pHLimeSoda AshSodium HydroxideHypochlorite

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Corrosion Control What is corrosionElectrochemical reaction by which metal is attackedChemicals causing corrosion in waterCarbon Dioxide

Hydrogen Sulfide

Dissolved oxygen

Galvanic corrosion (Galvanic series based type of metal)Most active metal gives up electrons to the least active – most active metal corrodesEx1: aluminum corrodes to stainless steelEx2: mild steel corrodes to copperEx3: Brass corrodes to copper

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Corrosion Control Factors effecting corrosionpHAlkalinity Calcium (hardness)ChloridesSulfatesTemperatureDissolved oxygen

Total dissolved solids

Natural organic matter

Bacteria (biofilm)

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Corrosion Control Factors effecting corrosion (continued)Stray currentDisinfection ResidualsWater age (detention time in distribution system)Age of pipe and fixturesCoatings and films Alkalinity and pH adjustmentDeposition of calcium carbonate

Corrosion inhibitors and sequestering agents

Corrosion by-products

Form on metal pipe and appurtenances over time

Slide14

Corrosion Control Water Treatment – AerationRemoves CO2Gas found in many water suppliesSurface waters have low levelsGround waters may be high in CO2Effects of carbon dioxideMakes water corrosive

Tends to keep iron in solution

Reacts with added lime causing pH to increase more slowly

Increases chemical costs

Slide15

Corrosion Control StabilityWater is stable when it neither dissolves nor deposits calcium carbonateStable pH for most waters is around 8.4Chemicals to raise pHLimeAdds hardness for soft watersAdds alkalinity for pH adjustment and to drive

floc

reactions

Soda AshSodium Hydroxide Langelier Saturation Index- testing stabilityPositive - depositionNegative - corrosiveThin coating of CaCO3 protects pipes

Slide16

Corrosion Control Langlier IndexUsed with physical/chemical analysisFormula in two parts:pHs = (9.30 + A + B) - ( C + D)Saturation index = pH - pHs

Components

A - Total Solids

B - Temperature °FC - Calcium Hardness (calcium content x 2.5)D - Alkalinity (total)

Slide17

Corrosion Control Passivating films and sequesturing agentsOrthophosphateDose based on water chemistryDoes not aide in sequesturing Iron(Fe) and Manganese(

Mn

)

Builds a Ca(PO4)(OH) film on pipe and fittings Requires 25 mg/l of Alkalinity and 5 mg/l of hardness to form filmpH for maximum effectiveness is 7.2 – 7.8Coupon tests are recommended but not absolutely necessary as long as water chemistry is sufficientZinc OrthophosphateNeeded for film formation in extremely soft watersAdvantage is protecting concrete and concrete lined pipeNot more effective for lead

Slide18

Corrosion Control Passivating films and sequesturing agentsPolyphosphate BlendsPolyphosphates blends prevent precipitation of Fe, Mn

, and Ca

Dose at 0.75 – 1.25 mg/l for corrosion control

Dose at 2 mg/l for each mg/l of Fe & Mn if sequesturingAdd after filtration if requiredCoupon tests should be conductedPolyphosphates can break down into simple phosphates

Slide19

Corrosion Control Lead controlpHBest between 8.0 and 10.0 but higher is usually better AlkalinityBest between 30 and 50 mg/l as CaCO3If > 74 mg/l as CaCO3 then pH < 8.4Calcium

Soft (low hardness), high alkalinity water is highly corrosive for lead

Chlorides and sulfates

Chlorides increase galvanic corrosion of lead in solder joints and brass fixturesSulfates decrease galvanic corrosion of lead in solder joints and brass fixturesGenerally chloride/sulfate ratio greater than 0.58 increases lead levels

Slide20

Corrosion Control Lead controlTemperatureHigher temps generally mean higher lead levelsNatural organic matter (TOC)Some NOM increases lead corrosion while some coats pipe and prevents itNom provides food for bacteria that may cause corrosion

Bacteria (

biofilm

)Some bacteria produce corrosive by productsSome bacteria may also increase the effectiveness of passivating film. Free chlorine residualPromotes lead oxide film which is generally protective ChloraminesRemoves lead oxide film

Slide21

Corrosion Control Copper controlpHBest between 8.0 and 10.0 but depends on alkalinity AlkalinityBest between 30 and 74 mg/l as CaCO3If > 74 mg/l as CaCO3 then pH >7.8 but higher alkalinities may require orthophosphate addition

Calcium

Minimum calcium hardness promotes formation of passivating films

Chlorides and sulfatesChlorides increase corrosion of copper pipe but it decreases over timeSulfates greatly increase pitting corrosion of copper pipe

Slide22

Corrosion Control Copper controlTemperatureHigher temps generally mean higher copper levelsNatural organic matter (TOC)NOM generally increases copper corrosion Nom provides food for bacteria that may cause corrosion

Bacteria (biofilm)

Some bacteria produce corrosive by products

Some bacteria may also increase the effectiveness of passivating film. Free chlorine residualincreases copper corrosion especially at higher residualsChloraminesNo documented increase

Slide23

Corrosion Control Concrete and concrete lined pipe pHLow pH can be highly corrosive to concrete pipe and liningsAlkalinityBest if > 60 mg/l as CaCO3Alkalinity in lining will leach into water until equilibrium is reached

Calcium

Calcium in lining will leach into water until equilibrium is reached

Chlorides and sulfatesSulfates dramatically increase concrete degradationSulfates promote specific bacterial growth which may increase concrete degradationGeneralLow pH, low alkalinity, low hardness water is highly corrosive to concrete

Slide24

Corrosion Control Cast iron pipe (iron)pHBest between 7.0 and 9.0Generally, higher pH produces more tuberculation but iron is less soluble Tuberculation can concentrate arsenic which can be released along with iron during periods of distribution upset (flow changes)Alkalinity

Best if > 60 mg/l as CaCO3

Calcium

Minimum calcium hardness promotes formation of passivating films Chlorides and sulfatesChlorides increase corrosion of iron but ratio to bicarbonate level more importantSulfates decrease corrosion of iron but may promote bacterial growth

Slide25

Corrosion Control Cast iron pipe (iron)TemperatureHigher temps generally mean higher iron levelsNatural organic matter (TOC)

NOM generally increases iron levels because it complexes metal ions

Nom provides food for bacteria that may cause corrosion

Bacteria (biofilm)Some bacteria produce corrosive by productsSome bacteria may also increase the effectiveness of passivating film. Free chlorine residualIncreases iron corrosion but not necessarily iron levelsChloraminesNo documented increase

Slide26

Corrosion Control Optimal corrosion control treatment (OCCT)the corrosion control treatment that minimizes the lead and copper concentrations at users’ taps while insuring that the treatment does not cause the water system to violate any national primary drinking water regulationsOCCT strategies are generally limited to three options (

Waterrf

2015)

The maintenance of oxidized conditions with high free chlorine residuals (typically>1 mg/L as Cl2) to form and maintain insoluble Pb(IV) scale,The control of pH and alkalinity (DIC),The use of orthophosphate within appropriate pH ranges.

Slide27

Lead Dissolution Sources of contaminationCorrosion of customer’s plumbing materials Lead service lines

Lead goose necks

Copper pipe with lead solder joints

Brass faucets and fixturesBronze faucets and fixturesStabilizers used in PVC manufacture in China, India, & othersLead pipe or lead jointed pipe owned by the utility

Slide28

Lead Dissolution What is utilities responsibility?In almost every case, excessive lead or copper comes from corrosion of plumbing materials within the water customer’s buildingProvide OCCTProvide information on proper faucet flush time

In a few cases, the excessive lead or copper is present in the source water

Provide removal treatment

Change sourceLead pipe owned by UtilityReplace or remove pipeProvide point of use devices in affected areas

Slide29

Lead(Pb) and Copper(Cu) RuleLead Absortion: Inorganic lead Only dissolved lead absorbed into the bodyMajority of Lead from plumbing corrosion is particulate not dissolvedLead is not absorbed at all if sufficient Calcium, iron, or Zinc is available in the diet

A long list of minerals will be absorbed before lead

Slide30

Lead(Pb) and Copper(Cu) RuleLead absorption example: soluble inorganic lead is added to deionized water and given to adult male.Fasting mode (doesn’t eat) 70% absorbed

No fasting mode (eats) 15% absorbed

Add calcium to water 1 – 2 % absorbed

In each condition above, it is estimated that the absorption for children under 5 years old and pregnant women will increase.

Slide31

Conflicting Rules All water treatment is employed to remove or neutralize a health related contaminant or aesthetic problem unacceptable to customers. Unfortunately, some treatments conflict. Ex:Corrosion treatments which decrease lead corrosion may increase copper corrosionNatural organic matter (NOM) generally decreases lead corrosion while increasing copper corrosion

Free chlorine residual decreases lead corrosion at higher pH while increasing copper corrosion especially at higher residuals

Chloramines dramatically increase lead dissolution (by stripping lead oxide film during change from free chlorine) but have no documented effect on copper

Disinfection changes are usually initiated because of violations of DBPR rule

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A Historical Perspective (children 1-5 yrs)

Slide39

Contact Information Questions?Contact InformationKeith Allen, P.E., BCEENeel-Schaffer, Eng. Inc.

601 421-1325

keith.allen@neel-schaffer.com

hkallen101@aol.com


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