mary nubbe-huntsville corrosion control program.pptx [read...
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Corrosion Control and
Measurement of Corrosion Control
Kevin Brakefield and Mary NubbeHuntsville UtilitiesOctober 2017
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Corrosion• Deterioration or destruction of a metal by chemical or
electrochemical reaction with its environment• Electrochemical reaction:
Metal dissolves at anode Electrons travel through metal to cathode; involved in reduction reactions
• For Iron Fe = Fe + 2 e oxidation2 H + 2 e = H reduction
• Concerns are pipe corrosion and leaching of metals• Lead and Copper – Lead service lines, copper pipe (lead
solder), brass materials in faucets and fittings
_2+
2+ _
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Corrosion Control – Huntsville Utilities• pH and alkalinity• Blended phosphate since May 2010• Formulation: 77% polyphosphate
23% orthophosphate• Orthophosphate – considered to be a passivator – forms a film or
protective layer that reduces the release of metals into the water• Polyphosphate – sequesters cations; and can revert to
orthophosphate• Huntsville Utilities initial dosing at 3 water plants – phased in over
a 16 month period• Initial doses were lower than present doses
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Goals of Corrosion Control – Huntsville Utilities
1. Corrosion control2. Consumer protection from leached metals originating from
pipe, solder, or fixtures3. Decrease in discolored water occurrences
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Measurements of Corrosion Control
• Corrosion Monitoring Linear Polarization Resistance 2 electrode probe set up,and data logger
• At widely distributed locations• Orthophosphate levels ‐ grab samples
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Linear Polarization Resistance LPR• Electrochemical method to measure corrosionElectrochemical Reactions• Produce or consume electrons• Rate of electron flow is a measurement of reaction rateFaraday’s Law of Electrolysis
m =
• Divide through by t and surface areato get corrosion rate
I t M
z F
wherem = mass reactingI = current (amps)t = time (sec)M = Atomic weightz = charge (valence)F = Faraday’s constant
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Linear Polarization Resistance LPR
• In reality, equations are more complicated• Equations attempt to reflect real behavior of system • Factors include current density, and activation
energy• Butler‐Volmer equation (kinetics of electrode
reactions), and related Tafel equations• Error analysis has shown that mass transport and
reverse partial reactions can also be important
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Huntsville Utilities• LPR probe and data logger configured to make a measurement
and convert to a corrosion rate in mils/year (0.001”/yr)• LPR measurements began in 2015 (one site), and several
additional sites in 2016• LPR probes at widely distributed locations in water system
Linear Polarization Resistance LPR• In practice – apply small potential between electrodes• Measure current • Resulting calculation of corrosion rate based on the Stern‐Geary
equation, which uses Butler‐Volmer and Tafel values
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Data Logger
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Data from Logger
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Dose 1: Initial
Dose 2: Increased
Dose 3: Increased
Water Plant
Start Date for Poly‐Ortho
Poly‐Ortho Dose (ppm)
Date of Change
Poly‐Ortho Dose (ppm)
Date of change
Poly‐Ortho Dose (ppm)
South Parkway May 2010 0.5 ‐ 0.6 Aug 2016 0.75 Oct 2016 1.0
Lincoln‐Dallas Mar 2011 1.0 Aug 2016 1.25 (no increase) 1.25Southwest Sep 2011 0.5 Aug 2016 0.75 Oct 2016 1.0
Ortho‐Poly Blended Phosphates at 3 WTP
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Corrosion Rates Initial Thru Dose 2
Dose 3 (current dose)
1st LPR reading to 20 Oct 16
21 Oct 16 to 29 Sep 17
Date of 1st LPR
ReadingSite Corrosion Rates, mils/year
1 3.78 2.26 22 Jul 162 1.04 0.37 5 Feb 163 1.89 0.89 5 Feb 164 2.05 0.90 22 Jul 165 2.42 1.85 29 Oct 156 2.90 1.30 22 Jul 16
All sites 2.32 1.37
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Corrosion and Orthophosphate
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
2016 May 10 2016 Aug 18 2016 Nov 26 2017 Mar 06 2017 Jun 14 2017 Sep 22 2017 Dec 31
Site 1 ‐ Corrosion
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
2016 May 10 2016 Aug 18 2016 Nov 26 2017 Mar 06 2017 Jun 14 2017 Sep 22 2017 Dec 31
Site 1 ‐ Orthophosphate
Corrosion in mils/year
Orthophosphate in mg/L
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Summary / Conclusions• This presentation is a description of the approach of the
corrosion control program used by Huntsville Utilities.• In all facets of treatment and data collection, it is considered
to be a work‐in‐progress.• A blended phosphate (77% poly and 23% ortho) has been
part of water treatment, starting in 2010.• The blended phosphate was started at lower doses; the
doses were increased over time. • Corrosion measurements by Linear Polarization Resistance
have been made at widely distributed sites, starting in 2015.
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Summary / Conclusions• In general, corrosion rates have decreased over time• Mean corrosion values for the initial dosing periods (lower
doses of blended phosphate) are higher than the corrosion values during the time period with increased blended phosphate
• Customer calls regarding discolored water have decreased substantially