Electrochemical corrosion measurements in concrete structures · PDF fileElectrochemical...
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Content
• Causes of corrosion damages in concrete structures• Monitoring methods• Previous measurements• New project
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Causes of corrosion damages in concretestructures
1: Rebar connected with a more noble material Galvanic corrosion
2-3: Optimum moisture condition for corrosion
4: Stray current corrosion
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Galvanic corrosion
• Differences in corrosion potential of the metals which are connected
• The ratio of anodic and cathodic areas (unnoble and noble areas).
• The electric conductivity of the electrolyte
• The oxygen concentration of the electrolyte
• The anodic and cathodic polarization behavior of the metals.
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Galvanisk spänningsserie (havsvatten, vid 20°C)
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Bimetallkorrosion - fråga
Lokal, kraftig, korrosion
Utbredda angrepp
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Stray current corrosion
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Stray current korrosion from HVDC transfer
• Long constructions in contact with water can suffer from stray currentcorrosion by HVDC transfer
• The risk of stray current corrosion increases with shorter distance tothe HVDC station
• Highest risk when the HVDC transfer is monopolar or unbalancedbipolar transfer
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Olika typer av HVDC-ledningar
”Monopolär”
”Bipolär”
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Stray current measurement, Forsmark (SKB Rapport TR-14-15, Elforsk rapport 10:84)Bertil Sandberg/Claes Taxén och B Sandberg et al.
About 4 volt difference.
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Monitoring methods
• Measure corrosion potential
• Measure corrosion current- LPR (linear polarisation resistance method)- Zero resistance ampere meter
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Corrowatch (force): For new constructions
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• Measure corrosion current with a zero resistance ampere meter
• Linear polarisation resistancemethod
Anode: ”rebar”cathode: titanium net
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CorroRisk (Force): For existing constructions
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• Measure corrosion current with a zero resistance ampere meter
• Linear polarisation resistancemethod
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Corrosion potential
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Previous measurements: Ringhals, coolingwater tunnels
• BackgroundThe consumption rate of sacrificial anodes was high. Why?Is there a risk of galvanic korrosion?
• Measurements: Corrosion rate and temperature over time.
• Corrosion potentialStainless steel in seawater: -100 mVRebar in water saturated concrete: -650 mVAluminium in seawater: -1000 mV
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Vänstra kanalen Högra kanalenRostfri pump
Berg Betong
Luft
Armering
Flöde av Havsvatten
Logger H-nära
Logger H-mitt
Logger H-bort
OfferanodLogger V-nära
Logger V-mitt
Logger V-bort
Rostfri pump
Armering
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Conclusion
• Galvanic corrosion risk: -100/200 mV in concrete with 1 weight-% Cl by weight ofcement. -300/400 mV with 2% Cl.
• The high consumption rate of sacrificial anodes was explained by a high potential difference between the anodes and rebar+stainlesssteel pump.
• The corrosion potential logger could detect potential differences withdistance from the pump and difference between the left and the right side.
• The measured potentials did not indicate galvanic corrosion
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New project
• Installation of corrosion potential loggers in cooling water tunnels.
• Determine the risk of galvanic corrosion and stray current korrosion.- condense pipes made of titanium, galvanic corrosion?- Is there a potential difference when HVDC transportation is changed?
• Measurements in ringhals, oskarshamn and possibly forsmark.
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