Cathodic Corrosion Protection in the Context of Lifetime ...
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![Page 1: Basic Corrosion and Cathodic Protection - …iranelectrical.com/wp-content/uploads/Basic_Corrosion_CP-slides.pdf · 1 Jeff Schramuk NACE CP Specialist #7695 Basic Corrosion and Cathodic](https://reader033.fdocuments.net/reader033/viewer/2022050702/5a6ffbdf7f8b9aa2538b8ea6/html5/thumbnails/1.jpg)
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Jeff SchramukNACE CP Specialist #7695
www.cpsolutionsinc.net
Basic Corrosion Basic Corrosion andand
Cathodic ProtectionCathodic Protection
Basic Corrosion & Cathodic Protection
![Page 2: Basic Corrosion and Cathodic Protection - …iranelectrical.com/wp-content/uploads/Basic_Corrosion_CP-slides.pdf · 1 Jeff Schramuk NACE CP Specialist #7695 Basic Corrosion and Cathodic](https://reader033.fdocuments.net/reader033/viewer/2022050702/5a6ffbdf7f8b9aa2538b8ea6/html5/thumbnails/2.jpg)
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Topics to be Covered
Why Should We Be Concerned about Corrosion?Definitions and TerminologyForms of CorrosionPipe Coatings and Cathodic ProtectionCathodic Protection using Magnesium AnodesAdvantages & Limitations of Galvanic Anode CP SystemsImpressed Current Cathodic Protection Measurement and Testing of CP SystemsField Test EquipmentCathodic Protection Criteria.
![Page 3: Basic Corrosion and Cathodic Protection - …iranelectrical.com/wp-content/uploads/Basic_Corrosion_CP-slides.pdf · 1 Jeff Schramuk NACE CP Specialist #7695 Basic Corrosion and Cathodic](https://reader033.fdocuments.net/reader033/viewer/2022050702/5a6ffbdf7f8b9aa2538b8ea6/html5/thumbnails/3.jpg)
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Why Should We Be Concerned about Corrosion?Definitions and TerminologyForms of CorrosionPipe Coatings and Cathodic ProtectionCathodic Protection using Magnesium AnodesAdvantages & Limitations of Galvanic Anode CP SystemsImpressed Current Cathodic Protection Measurement and Testing of CP SystemsField Test EquipmentCathodic Protection Criteria.
Basic Corrosion & Cathodic Protection
![Page 4: Basic Corrosion and Cathodic Protection - …iranelectrical.com/wp-content/uploads/Basic_Corrosion_CP-slides.pdf · 1 Jeff Schramuk NACE CP Specialist #7695 Basic Corrosion and Cathodic](https://reader033.fdocuments.net/reader033/viewer/2022050702/5a6ffbdf7f8b9aa2538b8ea6/html5/thumbnails/4.jpg)
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Effects of Infrastructure Corrosion
Life Safety
Economics Environmental
Regulatory Compliance
![Page 5: Basic Corrosion and Cathodic Protection - …iranelectrical.com/wp-content/uploads/Basic_Corrosion_CP-slides.pdf · 1 Jeff Schramuk NACE CP Specialist #7695 Basic Corrosion and Cathodic](https://reader033.fdocuments.net/reader033/viewer/2022050702/5a6ffbdf7f8b9aa2538b8ea6/html5/thumbnails/5.jpg)
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Why Should We Be Concerned about Corrosion?Definitions and TerminologyForms of CorrosionPipe Coatings and Cathodic ProtectionCathodic Protection using Magnesium AnodesAdvantages & Limitations of Galvanic Anode CP SystemsImpressed Current Cathodic Protection Measurement and Testing of CP SystemsField Test EquipmentCathodic Protection Criteria.
Basic Corrosion & Cathodic Protection
![Page 6: Basic Corrosion and Cathodic Protection - …iranelectrical.com/wp-content/uploads/Basic_Corrosion_CP-slides.pdf · 1 Jeff Schramuk NACE CP Specialist #7695 Basic Corrosion and Cathodic](https://reader033.fdocuments.net/reader033/viewer/2022050702/5a6ffbdf7f8b9aa2538b8ea6/html5/thumbnails/6.jpg)
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Corrosion Can be Defined as:
Practical Definition
Scientific Definition
The Tendency of a Metal to Revert to its Native State
Electrochemical Degradation of Metal as a Result of a Reaction with its Environment
![Page 7: Basic Corrosion and Cathodic Protection - …iranelectrical.com/wp-content/uploads/Basic_Corrosion_CP-slides.pdf · 1 Jeff Schramuk NACE CP Specialist #7695 Basic Corrosion and Cathodic](https://reader033.fdocuments.net/reader033/viewer/2022050702/5a6ffbdf7f8b9aa2538b8ea6/html5/thumbnails/7.jpg)
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Corrosion - A Natural Process
IRON OXIDE REFINING MILLING
IRON CORROSION IRON OXIDE
![Page 8: Basic Corrosion and Cathodic Protection - …iranelectrical.com/wp-content/uploads/Basic_Corrosion_CP-slides.pdf · 1 Jeff Schramuk NACE CP Specialist #7695 Basic Corrosion and Cathodic](https://reader033.fdocuments.net/reader033/viewer/2022050702/5a6ffbdf7f8b9aa2538b8ea6/html5/thumbnails/8.jpg)
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Four Basic Parts of a Corrosion Cell
Anode – A metal electrode in contact with the electrolyte which corrodesCathode - A metal electrode in contact with the electrolyte which is protected against corrosionElectrolyte – A solution or conducting medium such as soil, water or concrete which contains oxygen and dissolved chemicalsMetal Path – An external circuit that connects the anode and the cathode
![Page 9: Basic Corrosion and Cathodic Protection - …iranelectrical.com/wp-content/uploads/Basic_Corrosion_CP-slides.pdf · 1 Jeff Schramuk NACE CP Specialist #7695 Basic Corrosion and Cathodic](https://reader033.fdocuments.net/reader033/viewer/2022050702/5a6ffbdf7f8b9aa2538b8ea6/html5/thumbnails/9.jpg)
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Electron Flow vs. Conventional Current
Flow of conventional current is from positive (+) to negative (-)
Conventional current flow from (+) to (-) will be from the cathode to the anode in the metal path
Conventional current flow from (+) to (-) will be from the anode to the cathode in the electrolyte.
![Page 10: Basic Corrosion and Cathodic Protection - …iranelectrical.com/wp-content/uploads/Basic_Corrosion_CP-slides.pdf · 1 Jeff Schramuk NACE CP Specialist #7695 Basic Corrosion and Cathodic](https://reader033.fdocuments.net/reader033/viewer/2022050702/5a6ffbdf7f8b9aa2538b8ea6/html5/thumbnails/10.jpg)
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Anodic Area(Metal Loss)
DC Current
Cathodic Area
(Protected)
Definitions - Anodes & Cathodes
![Page 11: Basic Corrosion and Cathodic Protection - …iranelectrical.com/wp-content/uploads/Basic_Corrosion_CP-slides.pdf · 1 Jeff Schramuk NACE CP Specialist #7695 Basic Corrosion and Cathodic](https://reader033.fdocuments.net/reader033/viewer/2022050702/5a6ffbdf7f8b9aa2538b8ea6/html5/thumbnails/11.jpg)
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The Simplified Corrosion Cell
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1. Anode
2. Cathode
3. Electrolyte
4. Metal Path
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Components of a Familiar Corrosion Cell
CARBON ROD(Cathode)
ZINC CASE(Anode)
NH4 and Cl- Paste(Electrolyte)
WIRE(Metallic Path)
I
I
I
I
I
e-
![Page 13: Basic Corrosion and Cathodic Protection - …iranelectrical.com/wp-content/uploads/Basic_Corrosion_CP-slides.pdf · 1 Jeff Schramuk NACE CP Specialist #7695 Basic Corrosion and Cathodic](https://reader033.fdocuments.net/reader033/viewer/2022050702/5a6ffbdf7f8b9aa2538b8ea6/html5/thumbnails/13.jpg)
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Material Potential*Pure Magnesium -1.75Magnesium Alloy -1.60Zinc -1.10Aluminum Alloy -1.00Mild Steel (New) -0.70Mild Steel (Old) -0.50Cast / Ductile Iron -0.50Stainless Steel -0.50 to + 0.10Copper, Brass, Bronze -0.20Gold +0.20Carbon, Graphite, Coke +0.40* Potentials With Respect to Saturated Cu-CuSO4 Electrode
Less
Act
ive
Mor
e
Practical Galvanic Series*
![Page 14: Basic Corrosion and Cathodic Protection - …iranelectrical.com/wp-content/uploads/Basic_Corrosion_CP-slides.pdf · 1 Jeff Schramuk NACE CP Specialist #7695 Basic Corrosion and Cathodic](https://reader033.fdocuments.net/reader033/viewer/2022050702/5a6ffbdf7f8b9aa2538b8ea6/html5/thumbnails/14.jpg)
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Corrosion Reaction and Ohm’s Law
Ohm’s Law States that: I = ∆E/R where:
∆E = Driving Potential (EA minus EC)
EA = Anode Potential (measured in volts)
EC = Cathode Potential (measured in volts)
I = Current Flow (measured in amperes)
R = Resistance (measured in ohms)
![Page 15: Basic Corrosion and Cathodic Protection - …iranelectrical.com/wp-content/uploads/Basic_Corrosion_CP-slides.pdf · 1 Jeff Schramuk NACE CP Specialist #7695 Basic Corrosion and Cathodic](https://reader033.fdocuments.net/reader033/viewer/2022050702/5a6ffbdf7f8b9aa2538b8ea6/html5/thumbnails/15.jpg)
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Some Common Electrical Quantities
Current Flow: 1 ampere (A) = 1000 milliamps (mA)
Examples:
A sacrificial anode’s output is measured in mA
A CP rectifier’s output is can be up 100 A
Voltage: 1 volt (V) = 1000 millivolts (mV)
Examples:
A magnesium anode’s potential is ~1.6 V (1600 mV)
A CP rectifier can have a DC voltage of up to 100 V
![Page 16: Basic Corrosion and Cathodic Protection - …iranelectrical.com/wp-content/uploads/Basic_Corrosion_CP-slides.pdf · 1 Jeff Schramuk NACE CP Specialist #7695 Basic Corrosion and Cathodic](https://reader033.fdocuments.net/reader033/viewer/2022050702/5a6ffbdf7f8b9aa2538b8ea6/html5/thumbnails/16.jpg)
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Corrosion Cell - Anodic Reactions
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Corrosion Cell - Cathodic Reactions
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Corrosion Cell – Combined Reactions
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Fe2(OH)3
Fe2(OH)3
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![Page 19: Basic Corrosion and Cathodic Protection - …iranelectrical.com/wp-content/uploads/Basic_Corrosion_CP-slides.pdf · 1 Jeff Schramuk NACE CP Specialist #7695 Basic Corrosion and Cathodic](https://reader033.fdocuments.net/reader033/viewer/2022050702/5a6ffbdf7f8b9aa2538b8ea6/html5/thumbnails/19.jpg)
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Why Should We Be Concerned about Corrosion?Definitions and TerminologyForms of CorrosionPipe Coatings and Cathodic ProtectionCathodic Protection using Magnesium AnodesAdvantages & Limitations of Galvanic Anode CP SystemsImpressed Current Cathodic Protection Measurement and Testing of CP SystemsField Test EquipmentCathodic Protection Criteria.
Basic Corrosion & Cathodic Protection
![Page 20: Basic Corrosion and Cathodic Protection - …iranelectrical.com/wp-content/uploads/Basic_Corrosion_CP-slides.pdf · 1 Jeff Schramuk NACE CP Specialist #7695 Basic Corrosion and Cathodic](https://reader033.fdocuments.net/reader033/viewer/2022050702/5a6ffbdf7f8b9aa2538b8ea6/html5/thumbnails/20.jpg)
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General Corrosion
Corrosive environment is uniform around the structure
Anode area is uniformly distributed over the structure
Corrosion rate is usually constant over the structure
Environments where uniform attack can occur Atmospheric, Aqueous, Concrete
![Page 21: Basic Corrosion and Cathodic Protection - …iranelectrical.com/wp-content/uploads/Basic_Corrosion_CP-slides.pdf · 1 Jeff Schramuk NACE CP Specialist #7695 Basic Corrosion and Cathodic](https://reader033.fdocuments.net/reader033/viewer/2022050702/5a6ffbdf7f8b9aa2538b8ea6/html5/thumbnails/21.jpg)
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True Uniform Corrosive Attack
![Page 22: Basic Corrosion and Cathodic Protection - …iranelectrical.com/wp-content/uploads/Basic_Corrosion_CP-slides.pdf · 1 Jeff Schramuk NACE CP Specialist #7695 Basic Corrosion and Cathodic](https://reader033.fdocuments.net/reader033/viewer/2022050702/5a6ffbdf7f8b9aa2538b8ea6/html5/thumbnails/22.jpg)
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Galvanic Corrosion
When two different metals are connected and placed into a corrosive environment.Corrosion current is proportional to the difference in electrochemical energy between the two metalsArea Effect
Avoid small anode connected to a large cathode Distance Effect
Area closest to anode will have the greatest corrosion
![Page 23: Basic Corrosion and Cathodic Protection - …iranelectrical.com/wp-content/uploads/Basic_Corrosion_CP-slides.pdf · 1 Jeff Schramuk NACE CP Specialist #7695 Basic Corrosion and Cathodic](https://reader033.fdocuments.net/reader033/viewer/2022050702/5a6ffbdf7f8b9aa2538b8ea6/html5/thumbnails/23.jpg)
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Material Potential*Pure Magnesium -1.75Magnesium Alloy -1.60Zinc -1.10Aluminum Alloy -1.00Mild Steel (New) -0.70Mild Steel (Old) -0.50Cast / Ductile Iron -0.50Stainless Steel -0.50 to + 0.10Copper, Brass, Bronze -0.20Gold +0.20Carbon, Graphite, Coke +0.40* Potentials With Respect to Saturated Cu-CuSO4 Electrode
Less
Act
ive
Mor
e
Practical Galvanic Series*
![Page 24: Basic Corrosion and Cathodic Protection - …iranelectrical.com/wp-content/uploads/Basic_Corrosion_CP-slides.pdf · 1 Jeff Schramuk NACE CP Specialist #7695 Basic Corrosion and Cathodic](https://reader033.fdocuments.net/reader033/viewer/2022050702/5a6ffbdf7f8b9aa2538b8ea6/html5/thumbnails/24.jpg)
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Galvanic Corrosion Bimetallic Connection
![Page 25: Basic Corrosion and Cathodic Protection - …iranelectrical.com/wp-content/uploads/Basic_Corrosion_CP-slides.pdf · 1 Jeff Schramuk NACE CP Specialist #7695 Basic Corrosion and Cathodic](https://reader033.fdocuments.net/reader033/viewer/2022050702/5a6ffbdf7f8b9aa2538b8ea6/html5/thumbnails/25.jpg)
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Old Pipe (Cathode)
New Pipe (Anode)
Old-New Pipe Corrosion Cell
![Page 26: Basic Corrosion and Cathodic Protection - …iranelectrical.com/wp-content/uploads/Basic_Corrosion_CP-slides.pdf · 1 Jeff Schramuk NACE CP Specialist #7695 Basic Corrosion and Cathodic](https://reader033.fdocuments.net/reader033/viewer/2022050702/5a6ffbdf7f8b9aa2538b8ea6/html5/thumbnails/26.jpg)
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Steel in Concrete-Soil
Cathodic Zone
Anodic Zone
Concrete Encasement
Pipe in Soil Corrodes
Note: Arrows Indicate Direction of DC Current Flow
![Page 27: Basic Corrosion and Cathodic Protection - …iranelectrical.com/wp-content/uploads/Basic_Corrosion_CP-slides.pdf · 1 Jeff Schramuk NACE CP Specialist #7695 Basic Corrosion and Cathodic](https://reader033.fdocuments.net/reader033/viewer/2022050702/5a6ffbdf7f8b9aa2538b8ea6/html5/thumbnails/27.jpg)
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Dissimilar Surface Conditions
Pipe(Cathode) Threads
Bright Metal (Anode)
Scratches (Anode)
![Page 28: Basic Corrosion and Cathodic Protection - …iranelectrical.com/wp-content/uploads/Basic_Corrosion_CP-slides.pdf · 1 Jeff Schramuk NACE CP Specialist #7695 Basic Corrosion and Cathodic](https://reader033.fdocuments.net/reader033/viewer/2022050702/5a6ffbdf7f8b9aa2538b8ea6/html5/thumbnails/28.jpg)
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Concentration Cell Corrosion
Due to differences in the environment
Differential Soil Aeration – Very common
![Page 29: Basic Corrosion and Cathodic Protection - …iranelectrical.com/wp-content/uploads/Basic_Corrosion_CP-slides.pdf · 1 Jeff Schramuk NACE CP Specialist #7695 Basic Corrosion and Cathodic](https://reader033.fdocuments.net/reader033/viewer/2022050702/5a6ffbdf7f8b9aa2538b8ea6/html5/thumbnails/29.jpg)
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Aerated Soil
Differential Soil Aeration
Oxygen diffusing through backfill sustains corrosion to cathodic (top) area of pipe
Lack of oxygen at bottom of pipe creates relative corrosion cell to (top) area of pipe
Clay soil Clay soil
Anodic Zone
Cathodic Zone
O2 O2
![Page 30: Basic Corrosion and Cathodic Protection - …iranelectrical.com/wp-content/uploads/Basic_Corrosion_CP-slides.pdf · 1 Jeff Schramuk NACE CP Specialist #7695 Basic Corrosion and Cathodic](https://reader033.fdocuments.net/reader033/viewer/2022050702/5a6ffbdf7f8b9aa2538b8ea6/html5/thumbnails/30.jpg)
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Differential Aeration on Cast Iron Pipe
Cathodic Zone
Anodic Zone
![Page 31: Basic Corrosion and Cathodic Protection - …iranelectrical.com/wp-content/uploads/Basic_Corrosion_CP-slides.pdf · 1 Jeff Schramuk NACE CP Specialist #7695 Basic Corrosion and Cathodic](https://reader033.fdocuments.net/reader033/viewer/2022050702/5a6ffbdf7f8b9aa2538b8ea6/html5/thumbnails/31.jpg)
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Clay (moist low oxygen)
Sandy Loam (well drained, high oxygen)
Anode CathodeCathode
Differential Soil Aeration
Factors contributing to an increased corrosive attack are de-icing salts and agricultural fertilizers
Pavement
Sandy Loam (well drained, high oxygen)
![Page 32: Basic Corrosion and Cathodic Protection - …iranelectrical.com/wp-content/uploads/Basic_Corrosion_CP-slides.pdf · 1 Jeff Schramuk NACE CP Specialist #7695 Basic Corrosion and Cathodic](https://reader033.fdocuments.net/reader033/viewer/2022050702/5a6ffbdf7f8b9aa2538b8ea6/html5/thumbnails/32.jpg)
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Pitting Corrosion
Random and highly localized
Depth greater than area of attack
Most destructive form of corrosion
Pit location and growth difficult to predict
![Page 33: Basic Corrosion and Cathodic Protection - …iranelectrical.com/wp-content/uploads/Basic_Corrosion_CP-slides.pdf · 1 Jeff Schramuk NACE CP Specialist #7695 Basic Corrosion and Cathodic](https://reader033.fdocuments.net/reader033/viewer/2022050702/5a6ffbdf7f8b9aa2538b8ea6/html5/thumbnails/33.jpg)
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Pitting of Coated Carbon Steel in Soil
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External Pitting: Ductile Iron Water Main
![Page 35: Basic Corrosion and Cathodic Protection - …iranelectrical.com/wp-content/uploads/Basic_Corrosion_CP-slides.pdf · 1 Jeff Schramuk NACE CP Specialist #7695 Basic Corrosion and Cathodic](https://reader033.fdocuments.net/reader033/viewer/2022050702/5a6ffbdf7f8b9aa2538b8ea6/html5/thumbnails/35.jpg)
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Selective Leaching Corrosion
Selective LeachingGraphitization (Gray Cast Iron)
Dezincification (Brass)
![Page 36: Basic Corrosion and Cathodic Protection - …iranelectrical.com/wp-content/uploads/Basic_Corrosion_CP-slides.pdf · 1 Jeff Schramuk NACE CP Specialist #7695 Basic Corrosion and Cathodic](https://reader033.fdocuments.net/reader033/viewer/2022050702/5a6ffbdf7f8b9aa2538b8ea6/html5/thumbnails/36.jpg)
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Dealloying Corrosion (Graphitization)
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Why Should We Be Concerned about Corrosion?Definitions and TerminologyForms of CorrosionPipe Coatings and Cathodic ProtectionCathodic Protection using Magnesium AnodesAdvantages & Limitations of Galvanic Anode CP SystemsImpressed Current Cathodic Protection Measurement and Testing of CP SystemsField Test EquipmentCathodic Protection Criteria.
Basic Corrosion & Cathodic Protection
![Page 38: Basic Corrosion and Cathodic Protection - …iranelectrical.com/wp-content/uploads/Basic_Corrosion_CP-slides.pdf · 1 Jeff Schramuk NACE CP Specialist #7695 Basic Corrosion and Cathodic](https://reader033.fdocuments.net/reader033/viewer/2022050702/5a6ffbdf7f8b9aa2538b8ea6/html5/thumbnails/38.jpg)
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Eliminating the Corrosion Cell
Ano
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Cat
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Apply a Bonded Tape Wrapping
![Page 40: Basic Corrosion and Cathodic Protection - …iranelectrical.com/wp-content/uploads/Basic_Corrosion_CP-slides.pdf · 1 Jeff Schramuk NACE CP Specialist #7695 Basic Corrosion and Cathodic](https://reader033.fdocuments.net/reader033/viewer/2022050702/5a6ffbdf7f8b9aa2538b8ea6/html5/thumbnails/40.jpg)
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Pitting at a Coating Defect
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Coat the Structure & Electrically Isolate It
What’s Wrong Here?
![Page 42: Basic Corrosion and Cathodic Protection - …iranelectrical.com/wp-content/uploads/Basic_Corrosion_CP-slides.pdf · 1 Jeff Schramuk NACE CP Specialist #7695 Basic Corrosion and Cathodic](https://reader033.fdocuments.net/reader033/viewer/2022050702/5a6ffbdf7f8b9aa2538b8ea6/html5/thumbnails/42.jpg)
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Encase the Pipe in a “Corrosion Barrier”
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Why Should We Be Concerned about Corrosion?Definitions and TerminologyForms of CorrosionPipe Coatings and Cathodic ProtectionCathodic Protection using Magnesium AnodesAdvantages & Limitations of Galvanic Anode CP SystemsImpressed Current Cathodic Protection Measurement and Testing of CP SystemsField Test EquipmentCathodic Protection Criteria.
Basic Corrosion & Cathodic Protection
![Page 44: Basic Corrosion and Cathodic Protection - …iranelectrical.com/wp-content/uploads/Basic_Corrosion_CP-slides.pdf · 1 Jeff Schramuk NACE CP Specialist #7695 Basic Corrosion and Cathodic](https://reader033.fdocuments.net/reader033/viewer/2022050702/5a6ffbdf7f8b9aa2538b8ea6/html5/thumbnails/44.jpg)
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Corrosion occurs where current discharges from metal to electrolyte
The objective of cathodic protection is to force the entire surface to be cathodic to the environment.
How Cathodic Protection Works
![Page 45: Basic Corrosion and Cathodic Protection - …iranelectrical.com/wp-content/uploads/Basic_Corrosion_CP-slides.pdf · 1 Jeff Schramuk NACE CP Specialist #7695 Basic Corrosion and Cathodic](https://reader033.fdocuments.net/reader033/viewer/2022050702/5a6ffbdf7f8b9aa2538b8ea6/html5/thumbnails/45.jpg)
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Current is obtained from a metal of a higher energy level.
Galvanic Anode Cathodic Protection
![Page 46: Basic Corrosion and Cathodic Protection - …iranelectrical.com/wp-content/uploads/Basic_Corrosion_CP-slides.pdf · 1 Jeff Schramuk NACE CP Specialist #7695 Basic Corrosion and Cathodic](https://reader033.fdocuments.net/reader033/viewer/2022050702/5a6ffbdf7f8b9aa2538b8ea6/html5/thumbnails/46.jpg)
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Material Potential*Pure Magnesium -1.75Magnesium Alloy -1.60Zinc -1.10Aluminum Alloy -1.00Mild Steel (New) -0.70Mild Steel (Old) -0.50Cast / Ductile Iron -0.50Stainless Steel -0.50 to + 0.10Copper, Brass, Bronze -0.20Gold +0.20Carbon, Graphite, Coke +0.40* Potentials With Respect to Saturated Cu-CuSO4 Electrode
Less
Act
ive
Mor
e
Practical Galvanic Series*
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Cop
per
-200
mV
Ste
el -
600m
V
Mag
nesi
um -
1.7V
1. Anode
2. Cathode
3. Electrolyte
4. Metal Path
Galvanic Corrosion – No C.P. Benefit
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Cat
hode
Cat
hode
Ano
de
1. Anode
2. Cathode
3. Electrolyte
4. Metal Path
Galvanic Corrosion - Mitigated w/CP
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CP Performance - Can Be Verified
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Sacrificial Anode on a Buried Pipeline
Sacrificial Anode
Coating Defect
Connection to Pipe
Grade
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Coating Defect
Connection to Pipe
Grade
Sacrificial Anode
Sacrificial Anode w/Test Station
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CP Test Station - Terminal Board
structure lead wire
anode lead wire
insulated terminal board calibrated
shunt resistor
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Magnesium Anodes
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Proper distance of anode from pipeAt least 3’ from a coated pipe
At least 6’ from bare steel
At least 1’ deeper than pipeline
Evaluate pipe coating
Install anode carefully – don’t lift by the lead wire
Tamp earth firmly around anode package.
Packaged Magnesium Anode Natural Gas PL
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Leave slack in the anode lead wire
Wet area thoroughly around anode
Make a secure electrical connection to the pipe (e.g. exothermic weld)
Repair pipe coating to match original
Place test box where it is protected from damage and can be easily located
Do not allow any foreign pipeline contacts.
Packaged Magnesium Anode Natural Gas PL (cont.)
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Packaged Magnesium Anode Natural Gas PL (cont.)
*Detail courtesy of Midwest Energy Association*Detail courtesy of Midwest Energy Association
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Why Should We Be Concerned about Corrosion?Definitions and TerminologyForms of CorrosionPipe Coatings and Cathodic ProtectionCathodic Protection using Magnesium AnodesAdvantages & Limitations of Galvanic Anode CP SystemsImpressed Current Cathodic Protection Measurement and Testing of CP SystemsField Test EquipmentCathodic Protection Criteria.
Basic Corrosion & Cathodic Protection
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No external AC power is required
Effective utilization of protective current
Simple and inexpensive to install on new underground structures
Seldom cause stray DC interference
Minimal maintenance requirements.
Galvanic Anode CP Advantages
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Limited driving potential ∆E = (Ea – Ec)
Limited current output I = ∆E / Rt
Large number of anodes will be required on bare or poorly coated structures
Ineffective in high-resistivity soil environments (Rt ).
Galvanic Anode CP Limitations
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Why Should We Be Concerned about Corrosion?Definitions and TerminologyForms of CorrosionPipe Coatings and Cathodic ProtectionCathodic Protection using Magnesium AnodesAdvantages & Limitations of Galvanic Anode CP SystemsImpressed Current Cathodic ProtectionMeasurement and Testing of CP SystemsField Test EquipmentCathodic Protection Criteria.
Basic Corrosion & Cathodic Protection
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Rectifier
Anode Groundbed
( - ) ( + )
Pipeline(Structure)
Surface (Horizontal) Anode System
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Deep Anode (Vertical) Anode System
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Continuous Linear Anode System
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Impressed Current Transformer Rectifier
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Why Should We Be Concerned about Corrosion?Definitions and TerminologyForms of CorrosionPipe Coatings and Cathodic ProtectionCathodic Protection using Magnesium AnodesAdvantages & Limitations of Galvanic Anode CP SystemsImpressed Current Cathodic ProtectionMeasurement and Testing of CP SystemsField Test EquipmentCathodic Protection Criteria.
Basic Corrosion & Cathodic Protection
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Have you checked your rectifier lately?
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Monitoring Data for a CP Rectifier
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Can you locate your test stations?
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Potential Profile Survey Technique
Reference Cells
Test StationVoltmeter-Computer
Wire Dispenser & Distance Chainer
Pipeline
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Why Should We Be Concerned about Corrosion?Definitions and TerminologyForms of CorrosionPipe Coatings and Cathodic ProtectionCathodic Protection using Magnesium AnodesAdvantages & Limitations of Galvanic Anode CP SystemsImpressed Current Cathodic Protection Measurement and Testing of CP SystemsField Test EquipmentCathodic Protection Criteria.
Basic Corrosion & Cathodic Protection
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CP Test Equipment - Multi-Meters
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Multi-Meter Characteristics
Basic FunctionsReads AC & DC Volts
Reads Ohms (optional diode checker)
Reads AC and DC Amps (be careful here!)
Performance CriteriaField rugged, water/drop resistant
High input impedance (min. 20 M-Ω)
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Test Equipment Quality Assurance
Perform pre-test operational checks in accordance with
the manufacturer instructions
Verify the battery strength (if so equipped)
Initiate corrective action for equipment out of specification
Have the equipment calibrated each year
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Reference Electrode Basic Components
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Reference Electrode - Maintenance
Periodically verify cell against a known standardKeep porous plug covered when not usedClean and refill the reference cell annually
Clean copper rod with a non-metallic abrasive padReplace w/fresh Cu/CuSO4 solution (½ full at all times)Some Cu/CuSO4 crystals should always remain in suspensionWash hands after using – Cu/CuSO4 solution is hazardous
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P/S Potential Readings
Connect voltmeter to pipe and reference
Ensure reference cell plug has good contact with moist soil – not pavement
Place reference cell away from anodes
Read P/S on DCV scale
Record P/S reading using standard forms
If polarity is positive, notify corrosion dept.
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Meter Connections
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Why Should We Be Concerned about Corrosion?Definitions and TerminologyForms of CorrosionPipe Coatings and Cathodic ProtectionCathodic Protection using Magnesium AnodesAdvantages & Limitations of Galvanic Anode CP SystemsImpressed Current Cathodic Protection Measurement and Testing of CP SystemsField Test EquipmentCathodic Protection Criteria.
Basic Corrosion & Cathodic Protection
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Cathodic Protection Criteria-0.85 V (w/IR-drop consideration)-0.85 V Instant-Off100 mV polarization decayOther criteria determined to be “appropriate” by regulatory authority
DOT Standard – Part 192.463
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NACE International – CP Criteria
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DOT Standard – Part 192.465
Monitoring of Cathodic Protection
Potentials tested every 12 months at intervals not exceeding 15 months, or
10% per year to sample entire line every 10 years
Rectifiers and critical bonds checked every 2 months at intervals not exceeding 2-1/2 months.
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Do We Have a Good Reading?
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Questions?Questions?
Jeff SchramukNACE CP Specialist #7695
www.cpsolutionsinc.net
Basic Corrosion & Cathodic Protection