Corrosion Control K E I T H A L L E N , P. E . , B C E E AW WA T R A I N I N G M AY 1 7 , 2 0 1 6 Vulnerable Groups While 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 Pregnant
Already ill (immune system, medication) Immune compromised Allergies Specific diseases (Wilson disease Copper) Corrosion Control Particulate matter Most corrosion products are not dissolved They 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-availability Particulate matter does not contribute to metal availability for body function unless it can be dissolved by stomach acid in three hours EPA sample procedure requires 16 hours detention in mild acid to simulate the bioavailability component 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 bioavailable) 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 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 brass
Lead-tin solder joints (from chart results AWWA 2007) About 5% of particulate lead converted by EPA method is bioavailable About 1% of total particulate lead is bioavailable EPA method only captures 20% of the total particulate lead Lead pipe (pure lead particles) (from chart results AWWA 2007) About 60% of particulate lead converted by EPA method is bioavailable About 5% of total particulate lead is bioavailable EPA method only captures 10% of the total particulate lead Brass fittings (from chart results AWWA 2007) About 95% of particulate lead converted by EPA method is bioavailable About 80% of total particulate lead is bioavailable EPA method captures 85% of the total particulate lead Corrosion Control Is particulate lead that is not bioavailable a problem?
All samples exceeding action level are captured by EPA procedure Higher 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 2013 Change sampling procedures to better capture particulate matter? Change flushing instruction to be site specific? Change out everybodys plumbing?
Corrosion Control In water, dissolved substances separate into ions Ions are electrically charged particles Positive (+) Negative (-) Ex: Salt dissolves in water into sodium (Na+) and chlorine (Cl-) Compounds formed by ions Lime (calcium oxide - CaO) Soda Ash (sodium carbonate - Na CO ) 2 3 Baking Soda (sodium bicarbonate - Na2(HCO3)2) Corrosion Control pH or Hydrogen ion concentration Pure water doesnt exist in nature
pH ranges extends 0 to 14 Values less than 7.0 are acidic Values greater than 7.0 are basic Shallow 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 Corrosion Control Water alkalinity substances in water which neutralize acid
An increase, lowers acidity and raises pH Influences water corrosiveness Alkalinity is added when water contacts surrounding rocks and soil Hydroxyl (OH-) Carbonate (CO32-) Bicarbonate (HCO3-) At low pH, alkalinity in the form of H2CO3 (Carbonic Acid) Corrosion Control Chemicals lowering pH
Corrosion Control What is corrosion Electrochemical reaction by which metal is attacked Chemicals causing corrosion in water Carbon 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 corrodes Ex1: aluminum corrodes to stainless steel Ex2: mild steel corrodes to copper
Ex3: Brass corrodes to copper Corrosion Control Factors effecting corrosion pH Alkalinity Calcium (hardness) Chlorides Sulfates Temperature Dissolved oxygen
Total dissolved solids Natural organic matter Bacteria (biofilm) Corrosion Control Factors effecting corrosion (continued) Stray current Disinfection Residuals Water age (detention time in distribution system) Age of pipe and fixtures Coatings and films
Alkalinity and pH adjustment Deposition of calcium carbonate Corrosion inhibitors and sequestering agents Corrosion by-products Form on metal pipe and appurtenances over time Corrosion Control Water Treatment Aeration Removes CO2 Gas found in many water supplies Surface waters have low levels Ground waters may be high in CO2 Effects of carbon dioxide
Makes water corrosive Tends to keep iron in solution Reacts with added lime causing pH to increase more slowly Increases chemical costs Corrosion Control Stability Water is stable when it neither dissolves nor deposits calcium carbonate Stable pH for most waters is around 8.4 Chemicals to raise pH
Langelier Saturation Index- testing stability Lime Adds hardness for soft waters Adds alkalinity for pH adjustment and to drive floc reactions Soda Ash Sodium Hydroxide Positive - deposition Negative - corrosive Thin coating of CaCO3 protects pipes Corrosion Control Langlier Index Used with physical/chemical analysis
Formula in two parts: pHs = (9.30 + A + B) - ( C + D) Saturation index = pH - pHs Components A - Total Solids B - Temperature F C - Calcium Hardness (calcium content x 2.5) D - Alkalinity (total)
Corrosion Control Passivating films and sequesturing agents Orthophosphate Dose based on water chemistry Does 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 film pH for maximum effectiveness is 7.2 7.8 Coupon tests are recommended but not absolutely necessary as long as water chemistry is sufficient Zinc Orthophosphate
Needed for film formation in extremely soft waters Advantage is protecting concrete and concrete lined pipe Not more effective for lead Corrosion Control Passivating films and sequesturing agents Polyphosphate Blends Polyphosphates 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 sequesturing Add after filtration if required Coupon tests should be conducted Polyphosphates can break down into simple phosphates
Corrosion Control Lead control pH Alkalinity Best between 30 and 50 mg/l as CaCO3 If > 74 mg/l as CaCO3 then pH < 8.4 Calcium
Best between 8.0 and 10.0 but higher is usually better 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 fixtures Sulfates decrease galvanic corrosion of lead in solder joints and brass fixtures Generally chloride/sulfate ratio greater than 0.58 increases lead levels Corrosion Control Lead control Temperature
Natural organic matter (TOC) Promotes lead oxide film which is generally protective Chloramines Some bacteria produce corrosive by products Some bacteria may also increase the effectiveness of passivating film. Free chlorine residual
Some NOM increases lead corrosion while some coats pipe and prevents it Nom provides food for bacteria that may cause corrosion Bacteria (biofilm) Higher temps generally mean higher lead levels Removes lead oxide film Corrosion Control Copper control pH
Alkalinity Best between 30 and 74 mg/l as CaCO3 If > 74 mg/l as CaCO3 then pH >7.8 but higher alkalinities may require orthophosphate addition Calcium Best between 8.0 and 10.0 but depends on alkalinity Minimum calcium hardness promotes formation of passivating films Chlorides and sulfates
Chlorides increase corrosion of copper pipe but it decreases over time Sulfates greatly increase pitting corrosion of copper pipe Corrosion Control Copper control Temperature Natural organic matter (TOC)
increases copper corrosion especially at higher residuals Chloramines Some bacteria produce corrosive by products Some bacteria may also increase the effectiveness of passivating film. Free chlorine residual NOM generally increases copper corrosion Nom provides food for bacteria that may cause corrosion Bacteria (biofilm)
Higher temps generally mean higher copper levels No documented increase Corrosion Control Concrete and concrete lined pipe pH Alkalinity Calcium in lining will leach into water until equilibrium is reached
Chlorides and sulfates Best if > 60 mg/l as CaCO3 Alkalinity in lining will leach into water until equilibrium is reached Calcium Low pH can be highly corrosive to concrete pipe and linings Sulfates dramatically increase concrete degradation Sulfates promote specific bacterial growth which may increase concrete degradation General
Low pH, low alkalinity, low hardness water is highly corrosive to concrete Corrosion Control Cast iron pipe (iron) pH Alkalinity Best if > 60 mg/l as CaCO3 Calcium
Best between 7.0 and 9.0 Generally, 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) Minimum calcium hardness promotes formation of passivating films Chlorides and sulfates Chlorides increase corrosion of iron but ratio to bicarbonate level more important Sulfates decrease corrosion of iron but may promote bacterial growth Corrosion Control Cast iron pipe (iron) Temperature
Natural organic matter (TOC) Some bacteria produce corrosive by products Some bacteria may also increase the effectiveness of passivating film. Free chlorine residual NOM generally increases iron levels because it complexes metal ions Nom provides food for bacteria that may cause corrosion
Bacteria (biofilm) Higher temps generally mean higher iron levels Increases iron corrosion but not necessarily iron levels Chloramines No documented increase 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 regulations OCCT 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. Lead Dissolution Sources of contamination Corrosion of customers plumbing materials Lead service lines
Lead goose necks Copper pipe with lead solder joints Brass faucets and fixtures Bronze faucets and fixtures Stabilizers used in PVC manufacture in China, India, & others Lead pipe or lead jointed pipe owned by the utility Lead Dissolution What is utilities responsibility? In almost every case, excessive lead or copper comes from corrosion of plumbing materials within the water customers building In a few cases, the excessive lead or copper is present in the source water
Provide OCCT Provide information on proper faucet flush time Provide removal treatment Change source Lead pipe owned by Utility Replace or remove pipe Provide point of use devices in affected areas Lead(Pb) and Copper(Cu) Rule Lead Absortion: Inorganic lead
Only dissolved lead absorbed into the body Majority of Lead from plumbing corrosion is particulate not dissolved Lead 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 Lead(Pb) and Copper(Cu) Rule Lead absorption example: soluble inorganic lead is added to deionized water and given to adult male. Fasting mode (doesnt 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. 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 corrosion Natural 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 A Historical Perspective (children 1-5 yrs) Contact Information Questions? Contact Information Keith Allen, P.E., BCEE Neel-Schaffer, Eng. Inc. 601 421-1325 [email protected][email protected]
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