CATHODIC PROTECTION - OISD

CATHODIC PROTECTIONMONITORING EFFECTIVENESS

ByDr M B Mishra

Corrosion Consultant

Presented At

O.I.S.D. WorkshopCritical Safety Issues In Marketting

OperationsStriving For Improved Performance

January,16,2014

CORROSION[ METAL DEGRADATON DUE TO REACTING WITH

ENVIRONMENT ]RAVAGES VALUABLE ASSETS SUCH AS :

PIPELINES [UNDERGROUND / ABOVE GROUND]

TANKS[UNDERGROUND/ABOVE GRADE/MOUNDED]

RUTOR STEEL IN CONCRETE

STRUCTURALSOTHER ASSETS [PACE MAKER,JOINTS,DENTAL]

CORROSIONRESULTS IN RUPTURE

CAUSINGHAZARDS – FIRE,POLLUTION,FATALITY

[HUMAN,FLORA,FAUNA]BESIDES

ECONONMIC LOSSESDUE TO

PRODUCT LOSS,REPAIR COST,DOWN TIME &COMPENSATION

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PIPELINE FAILURES

• ONCE PIPELINE LEAKCOMMENCES ITPROGRESSES INEXPONENTIAL RATE.

• CORROSION CAN BECONTROLLEDWITHIN ACCEPTABLELIMITS BYAPPLICATION OFCATHODICPROTECTION FROMCONSTRUCTIONSTAGE.

FAILURE RATE COMPARISION

PITTING NEAR THE JOINT AREA

PIPELINE COATINGS AFTER EXCAVATION

Nace Corrosion 2004

TANK BOTTOM PLATE PITTING CORROSION

PIPE RUPTURE

SEVERE CORROSION

FAILURE FROM THE SEAM

CORROSION CONTROL

• THE EFFORT IS TO MINIMIZE CORROSION,ANATURAL PHENOMENON,TO AN ACCEPTABLELIMIT SO THAT ECONOMIC VIABILITY ISENSURED

• THIS IS BEST ACHIEVED BY PROVIDING ASUITABLE COATING SUPPLEMENTED BY ACOMPATIBLE CATHODIC PROTECTION SYSTEM

AS A COMPOSITECORROSION PROTECTION SYSTEM

CORROSION• Corrosion Reactions :• Fe ↔ Fe ++ + 2e- Anodic Reaction (1)• 2e- + 2H+ ↔ 2H →H2

• Or H2O +2e- +½ O2 →2(OH-)• Fe++ + 2OH- -------› Fe (OH)2

• Fe (OH)2 + ½ O2 +½ H2 O--------› Fe (OH)3[Green Colour]

• 2Fe (OH)3 --------›2 Fe 2 O 3 +3 H2 O[Rust, Brown colour]

•

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DISCRETE IMPRESSED CURRENT ANODES

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EFFECTS OF SOIL RESISTIVITY ON CURRENTDISTRIBUTION

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EFFECTS OF SOIL PROPERTIES ON CURRENTDISTRIBUTION

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CATHODIC PROTECTION

• IMPRESSED CURRENT CATHODICPROTECTION SYSTEM IS THE SECONDMETHOD AVAILABLE TO PROTECT THEUNDERGROUND UTILITIES FOR LONGERDURATIONS (UPTO 50 YEARS) AS IN THIS THEPOWER SOURCE & HENCE THE PROTECTIVECURRENT CAN BE CONTROLLED ASREQUIRED TO PROVIDE ADEQUATEPROTECTION THROUGHOUT. THIS INVOLVESUSE OF FOLLOWING ANODES;

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REFERENCE ELECTRODES

• TO MEASURE REPRODUCIBLE [P-S-P] THEFOLLOWING REFERENCE HALF CELL ARE INUSE

Cu-CuSO4(V) Zn(V) Ag-AgCl(V)

(-)0.75 (+)0.35 (-)0.7

(-)0.85 (+)0.25 (-)0.8

(-)1.0 (+)0.1 (-)0.95

(-)1.2 (-)0.1 (-)1.15

(-)1.5 (-)0.4 (-)1.45

(-)2.0 (-)0.9 (-)1.95

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CRITERIA FOR CATHODIC PROTECTION

• THREE PRIMARY CRITERIA FOR CATHODICPROTECTION OF UNDERGROUND ORSUBMERGED STEEL OR CAST IRON PIPEARE : (-)0.85V w.r.t. Cu-CuSO4 HALF CELL

REFERENCE ELECTRODE WITHPROTECTIVE CURRENT FOR CATHODICPROTECTION SYSTEM-APPLIED (ON). (-)0.85V w.r.t. Cu-CuSO4 HALF CELL

REFERENCE ELECTRODE WITHPROTECTIVE CURRENT FOR CATHODICPROTECTION SYSTEM-NOT APPLIED(INSTANT OFF).

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CRITERIA FOR CATHODIC PROTECTION

100mV POLARISATION VOLTAGE.

300mV SHIFT FROM NATURALPOTENTIALS WITH PROTECTIVECURRENT APPLIED (ON).

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POTENTIAL DISTRIBUTION ALONG THEPIPELINE

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PIPELINE COATING AND CATHODICPROTECTION SYSTEM ASSESSMENT

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PIPELINE COATING AND CATHODICPROTECTION SYSTEM ASSESSMENT

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CATHODIC PROTECTION FOR ABOVE GROUNDSTORAGE TANK BOTTOMS

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CATHODIC PROTECTION FOR ABOVE GROUNDSTORAGE TANK BOTTOMS

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CATHODIC PROTECTION FOR ABOVE GROUNDSTORAGE TANK BOTTOMS

Nace Corrosion 2004

Installation of the Anodeflex System. It provides Cathodic Protection on everypoint without causing any under or overprotection

COATING AND CATHODICPROTECTION SYSTEM ASSESSMENT

Nace Corrosion 2004

REF. ELECTRODE

CONCEPTUAL DESIGN OF CP FORBULLET TANKS

SAND MOUND

TOTR UNIT

POLYMERIC ANODE

LPG BULLET

INLINE

SPLICE

CONNECTINGCABLES

Nace Corrosion 2004

LONG LINE POLYMERIC ANODE SYSTEM FORMOUNDED BULLET

Nace Corrosion 2004

CONCEPTUAL DESIGN OF CP FOR BULLET TANKS

POLYMERIC ANODE

LPG BULLET

INLINE

SPLICE

CONNECTINGCABLES

TRUNIT

AJB

CJB

REJB

+ ve- ve

Ref Cell

ISOLATING JOINTPOLARIZATON

CELLEARTHING

Nace Corrosion 2004

REF. ELECTRODE

CONCEPTUAL DESIGN OF CP FOR BULLET TANKS

BULLET-2

SAND MOUND

POLYMERIC ANODE

BULLET-1

Corrosion Monitoring

• Cathodic Protection Of Assets EnsuresPrevention of Loss of Metal to Earth due toSoil-side Corrosion

• This is a Dynamic Process & Requires CloseMonitoring of C P Parameters

• If C P System Fails or is not performing as perDesign,Corrosion Protection is In-Effective

• The Efficacy Of C P depends on continuousMonitoring to Ensure Desired Level ofParameters

Corrosion Monitoring

• Pipe to Soil Potential [P-S-P] is Monitored[P-S-P] Vs CSE to be in the Range(-)0.85 Minimum to (-) 1.5 V Maximum when AnaerobicBacteria are absent [No SRB]

and (-)0.95 Minimum to (-) 1.5 V Maximum when [SRB]arepresent

Corrosion Monitoring• Only High Impedance Voltmeter to be used• Equipment of Standard make & proven

capability to be used• Multichannel Recording capability• The Record should be field verifiable through

computer display in field• Recorded Data should be Downloaded

Corrosion Monitoring

• For this Reason it is vitally importantthat utility Operators Maintainaccurate,Integrated Information on theirutility system from construction andInstallation throughOperataion,Inspection & Maintenance

Corrosion Monitoring

• The Key to Integrity ManagementProgramme is :

1. To Know where PotentialProblems Lie

2. To Understand How Severe theProblem might be

3. How Best to Manage theseProblems

Corrosion Monitoring

• Survey Data to be Collated for DecipheringProblem Areas & Effective Measures tocounter the problems detected

• Post Mitigative Measures installation Furthersurveys to evaluate Adequacy of installedmitigative measures

• Frequency of such surveys thereafterperiodically

Corrosion MonitoringConclusion

• The Safety factor question has been settledmany times by Research,Experience and Tests.

• In service underground utilities are safe ifthey are maintained properly and protectedagainst Corrosion,that Devours the Vitalsunchecked and undetected,and third partydamage.

AcknowledgementsGrateful Thanks To O.I.S.D.

For this Opportunity to Share My Perceptions& Experience on Cathodic ProtectionMonitoring With Such August AudienceComprising OfEngineering,Consultancy,Operations,Maintenance,Inspection,Cosntruction &Trouble Shooting Fraternity.

THANKS•