Transcript Presentation - AL/MS Section of AWWA

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:
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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
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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
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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)
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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?
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In general, current EPA analysis will vastly overestimate bio-availability of
particulate lead except that from brass
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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?
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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?
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Ban lead in brass fitting – 2013
Change sampling procedures to better capture particulate matter?
Change flushing instruction to be site specific?
Change out everybody’s 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 - Na2CO3)
 Baking Soda (sodium bicarbonate - Na2(HCO3)2)
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Corrosion Control
 pH or Hydrogen ion concentration
Pure water doesn’t 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
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Electrodes (pH meter)
 Color matching equipment
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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-)
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At low pH, alkalinity in the form of H2CO3 (Carbonic Acid)
Corrosion Control
 Chemicals lowering pH
Chlorine
 Alum
 Sulfuric Acid
 Hydrofluosilicic Acid
 Carbon Dioxide
 Carbonic Acid
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 Chemicals raising pH
Lime
 Soda Ash
 Sodium Hydroxide
 Hypochlorite
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Corrosion Control
 What is corrosion
 Electrochemical reaction by which metal is attacked
 Chemicals causing corrosion in water
Carbon Dioxide
 Hydrogen Sulfide
 Dissolved oxygen
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Galvanic corrosion (Galvanic series based type of metal)
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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
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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
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Corrosion Control
 Stability
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Water is stable when it neither dissolves nor deposits calcium carbonate
Stable pH for most waters is around 8.4
Chemicals to raise pH
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Lime
 Adds hardness for soft waters
 Adds alkalinity for pH adjustment and to drive floc reactions
Soda Ash
Sodium Hydroxide
Langelier Saturation Index- testing stability
Positive - deposition
 Negative - corrosive
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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)
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Corrosion Control
 Passivating films and sequesturing agents
 Orthophosphate
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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
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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
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pH
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Alkalinity
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Best between 30 and 50 mg/l as CaCO3
If > 74 mg/l as CaCO3 then pH < 8.4
Calcium
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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
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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
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Natural organic matter (TOC)
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Promotes lead oxide film which is generally protective
Chloramines
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Some bacteria produce corrosive by products
Some bacteria may also increase the effectiveness of passivating film.
Free chlorine residual
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Some NOM increases lead corrosion while some coats pipe and prevents it
Nom provides food for bacteria that may cause corrosion
Bacteria (biofilm)
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Higher temps generally mean higher lead levels
Removes lead oxide film
Corrosion Control
 Copper control
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pH
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Alkalinity
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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
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Best between 8.0 and 10.0 but depends on alkalinity
Minimum calcium hardness promotes formation of passivating films
Chlorides and sulfates
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Chlorides increase corrosion of copper pipe but it decreases over time
Sulfates greatly increase pitting corrosion of copper pipe
Corrosion Control
 Copper control
 Temperature
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Natural organic matter (TOC)
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increases copper corrosion especially at higher residuals
Chloramines
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Some bacteria produce corrosive by products
Some bacteria may also increase the effectiveness of passivating film.
Free chlorine residual
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NOM generally increases copper corrosion
Nom provides food for bacteria that may cause corrosion
Bacteria (biofilm)
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Higher temps generally mean higher copper levels
No documented increase
Corrosion Control
 Concrete and concrete lined pipe
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pH
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Alkalinity
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Calcium in lining will leach into water until equilibrium is reached
Chlorides and sulfates
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Best if > 60 mg/l as CaCO3
Alkalinity in lining will leach into water until equilibrium is reached
Calcium
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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
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Low pH, low alkalinity, low hardness water is highly corrosive to concrete
Corrosion Control
 Cast iron pipe (iron)
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pH
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Alkalinity
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Best if > 60 mg/l as CaCO3
Calcium
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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
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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
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Natural organic matter (TOC)
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Some bacteria produce corrosive by products
Some bacteria may also increase the effectiveness of passivating film.
Free chlorine residual
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NOM generally increases iron levels because it complexes metal ions
Nom provides food for bacteria that may cause corrosion
Bacteria (biofilm)
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Higher temps generally mean higher iron levels
Increases iron corrosion but not necessarily iron levels
Chloramines
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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)
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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 customer’s 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
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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 customer’s building
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In a few cases, the excessive lead or copper is present in the source
water
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Provide OCCT
Provide information on proper faucet flush time
Provide removal treatment
Change source
Lead pipe owned by Utility
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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
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Lead(Pb) and Copper(Cu) Rule
 Lead absorption example: soluble inorganic lead is
added to deionized water and given to adult male.
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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.
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:
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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]