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•