Cathodic Protection and Interferences - · PDF fileCathodic protection and interferences • Corrosion • Cathodic protection • Protection criterion • ON potential measurements

Cathodic Protection and Cathodic Protection and Cathodic Protection and Cathodic Protection and InterferencesInterferences

René GregoorRené Gregoor

Madrid June 18Madrid June 18thth and 19and 19thth 20092009

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Madrid, June 18Madrid, June 18thth and 19and 19thth 20092009

Cathodic protection and interferencesCathodic protection and interferences•• CorrosionCorrosion•• Cathodic protectionCathodic protection•• Protection criterionProtection criterion•• ON potential measurementsON potential measurements•• DC Interferences and mitigation measuresDC Interferences and mitigation measures•• AC Interferences and mitigation measuresAC Interferences and mitigation measures•• ConclusionsConclusions

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Corrosion processCorrosion process

Corrosion, a natural process ...Corrosion, a natural process ...

reduction

ore =metal oxides metal

oxidation

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Corrosion mechanismCorrosion mechanism

OH-

Cathodic areaCathodic area O

OO

H

He-

Cathodic areaCathodic area

e-

OH- O

OH-

H

(Reduction)

e-

e Current entering the metalCurrent entering the metalOH-

Fe++Anodic areaAnodic area

e-

(Oxidation) Fe++

Cl-

ElectrolyteElectrolyteFeFeCurrent leaving the metalCurrent leaving the metal

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yy

ElectroElectro--chemical reactionschemical reactions

•• AnodeAnodeFe FeFe Fe2+2+ + 2e+ 2e-- ( oxidation)( oxidation)

•• CathodeCathodeOO22 + 2H+ 2H22O + 4eO + 4e-- 4OH4OH-- (reduction O(reduction O22))

2H2H22O + 2eO + 2e-- HH22 + 2OH+ 2OH-- (reduction H(reduction H22O)O)

2H2H++ + 2e+ 2e-- HH22

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Measures against corrosionMeasures against corrosion

•• Electrical isolating coating to limit Electrical isolating coating to limit h l f i i h h l lh l f i i h h l l•• the metal surface area in contact with the electrolytethe metal surface area in contact with the electrolyte

•• the required cathodic protection currentsthe required cathodic protection currents•• interferences to third party infrastructureinterferences to third party infrastructureinterferences to third party infrastructureinterferences to third party infrastructure

•• Cathodic protection toCathodic protection to•• protect from corrosion at coating defectsprotect from corrosion at coating defects•• protect from DC stray currents protect from DC stray currents

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Cathodic protection installationCathodic protection installation

•• TransformerTransformer--rectifier to produce DC currentrectifier to produce DC current

•• Anode bed Anode bed

•• CP test postsCP test posts•• Reference electrodes Reference electrodes

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Cathodic protection installationCathodic protection installation

Transformer-rectifier

~ - +

pipelineFeSi or titanium oxide coated

p p

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TransformerTransformer--rectifier rectifier

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Titanium oxide coated anodeTitanium oxide coated anode

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Protection criterion (as OFF potential)Protection criterion (as OFF potential)•• European standard EN12954:2001 fixes the protection criterion European standard EN12954:2001 fixes the protection criterion

for iron in soil as the potential more negative than for iron in soil as the potential more negative than --850 mV 850 mV (Cu/CuSO(Cu/CuSO4 4 reference electrode) reference electrode)

•• European standard EN13509:2003 defines the measurement European standard EN13509:2003 defines the measurement techniques to be appliedtechniques to be appliedtechniques to be appliedtechniques to be applied

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Limits according to EN12954:2001 Limits according to EN12954:2001

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ON potential measurementON potential measurement

V Reference electrode

(h lf ll)(half cell)

pipelineelectrolyteelectrolyte

(half cell)

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ON potential measurementON potential measurement

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DC stray currentsDC stray currents

•• from cathodic protection installations, relatively constant, from cathodic protection installations, relatively constant, mitigated bymitigated by•• direct bond (cable)direct bond (cable)•• direct bond (cable)direct bond (cable)•• resistive bond resistive bond

•• from DC traction systems (train, tramway, metro, …), highly from DC traction systems (train, tramway, metro, …), highly variable, mitigated byvariable, mitigated by•• unidirectional drainage in substationsunidirectional drainage in substationsunidirectional drainage in substationsunidirectional drainage in substations•• forced drainage on railsforced drainage on rails

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Cathodic protection (CP system)Cathodic protection (CP system)

anodeanodetransformertransformer--rectifierrectifier

protected pipelineprotected pipeline

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Stray currents from CP systemsStray currents from CP systems

third party pipelinethird party pipeline

anodeanodetransformertransformer--rectifierrectifier

iicorrosioncorrosionpossiblepossible

protected pipelineprotected pipeline

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Stray currents from CP systems Stray currents from CP systems -- RemediesRemedies

third party pipelinethird party pipelineanodeanode

transformertransformer--rectifierrectifier

R = R ouR = R ouR = 0R = 0R = 0R = 0

protected pipelineprotected pipeline

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Stray currents from DC traction systemsStray currents from DC traction systems

+SS -SS

pipelinecorrosioncorrosion protectionprotection

0potentiel

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Stray currents from DC traction Stray currents from DC traction -- RemediesRemedies

+SS -SS

pipelineprotectionprotection

0potential

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Highly variable stray currents from DC traction systemsHighly variable stray currents from DC traction systems

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Forced drainage along the railsForced drainage along the rails

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Induced AC from High Voltage Power LinesInduced AC from High Voltage Power Lines

•• Transformer effect between HV Transformer effect between HV power lines (primary) and a power lines (primary) and a metal structure in parallel metal structure in parallel pp(secondary)(secondary)

•• Interfering structuresInterfering structures•• high voltage power lineshigh voltage power lineshigh voltage power lines high voltage power lines

pour transport of electricitypour transport of electricity•• high voltage power lines high voltage power lines

and catenaries of high and catenaries of high speed trainsspeed trains

•• Interfered structures Interfered structures •• long metal pipelineslong metal pipelinesgg•• electricity cableselectricity cables

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Induced AC from High Voltage Power LinesInduced AC from High Voltage Power Lines•• Amplitude of induced AC depends onAmplitude of induced AC depends onAmplitude of induced AC depends on Amplitude of induced AC depends on

•• length of parallelism and the distance between HV power length of parallelism and the distance between HV power line and the pipelineline and the pipeline

il i ti itil i ti it•• soil resistivitysoil resistivity•• electrical characteristics of the HV power lineelectrical characteristics of the HV power line•• electrical characteristics of the pipelineelectrical characteristics of the pipelineelectrical characteristics of the pipelineelectrical characteristics of the pipeline•• type of isolating coating of the pipelinetype of isolating coating of the pipeline

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Induced AC voltageInduced AC voltage•• MagnitudeMagnitude•• MagnitudeMagnitude

•• Some volt to some tens of volt under normal interferenceSome volt to some tens of volt under normal interference•• Limits within the framework of corrosion (Cu/CuSOLimits within the framework of corrosion (Cu/CuSO44) as ) as (( 44))

recommended in CEN TS15280recommended in CEN TS15280•• < 4 V if specific soil resistivity < 25 ohm.m< 4 V if specific soil resistivity < 25 ohm.m•• < 10 V if specific soil resistivity > 25 ohm m< 10 V if specific soil resistivity > 25 ohm m•• < 10 V if specific soil resistivity > 25 ohm.m< 10 V if specific soil resistivity > 25 ohm.m

•• Remedies on existing pipelinesRemedies on existing pipelines•• Grounding of AC part using special electronic circuitsGrounding of AC part using special electronic circuits

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ConclusionConclusion•• Cathodic protection is simple as a principle but complex in itsCathodic protection is simple as a principle but complex in its•• Cathodic protection is simple as a principle but complex in its Cathodic protection is simple as a principle but complex in its

applicationapplication

•• Design of CP installations, followDesign of CP installations, follow--up of the polarization potential of up of the polarization potential of the pipelines, evaluation of the interference situation is a matter the pipelines, evaluation of the interference situation is a matter for expertsfor experts

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Thank you for your attentionThank you for your attention

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