corrosion cells in action - aucsc
TRANSCRIPT
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Corrosion Cells In Action
Chapter 1
Appalachian Underground Corrosion
Short Course
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Introduction
Review of Basic Concepts
The Chemistry of Corrosion
Electromotive/Galvanic Series
Galvanic Corrosion Examples
Corrosion Cells in Action
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Why are we Here?
Corrosion Costs
440 Billion Annually
Why?
Iron Ore
(oxide)Refine
Products
(Pipe)
Corrosion
(oxide)
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Basic Concepts
Four Essential Elements of Corrosion Cell
Anode
Cathode
Conductive Electrolyte
– In contact with both anode and cathode
Metallic Conductor
– Connecting anode and cathode
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Basic Concepts
Anode
Discharges Ions (Oxidation Reactions)
Location of Current Discharge
Corrodes
Cathode
Collects Ions (Reduction Reactions)
Location of Current Pickup
Protected
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Basic Concepts
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Basic Concepts
Combined Reactions
Fe + 2H2O Fe++ + 2H+ + 2(OH)-
Fe++ + 2(OH)- Fe(OH)2
Ferrous Hydroxide
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Dry Cell Example
Zinc Can
(Anode)Zn+2
H2
+
-Carbon Rod
(cathode)
NH4Cl Solution
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Electromotive Force
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Potential Measurements
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Potential Measurements850
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Cathodic
Anodic
Practical Galvanic
Series in Seawater
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Practical
Galvanic
Series in
Soil
Anodic
Cathodic
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Galvanic Corrosion Examples
Dissimilar Metal Couple
Non-Homogeneous Soils
Differential Aeration/Chemistry
Dissimilar Surface Conditions
Stray Current
Effect of Stress
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Dissimilar Metal Couple
Corroding Corroding
Protected
Protected
Corroding
Black Steel Pipe
Cast Iron Valve
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Non-Homogeneous Soil
Sandy Soil Clayey Soil
CorrodingProtected
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Differential Aeration
Oxygen Poor Packed Soil
Oxygen Rich Loose Soil
Anode
Cathode
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Differential Aeration
Road
Poorly AeratedOxygen
Rich
Loose Soil
AnodeCathode Cathode
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Dissimilar Surface Conditions
Corroding Protected
New Pipe Old Pipe
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Dissimilar Surface Conditions
Corroding Protected
New Pipe Mill Scale
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Stray Current
CorrodingStray Current
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Dissimilar Metal Couple
Mg MgMg
Beneficial Sacrificial Protection
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Effect of Stress
Tensile Load Tensile Load
Highly Stressed Area
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Cathodic ProtectionRectifier
Goundbed
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Corrosion Cells
Developed by Col George. C. Cox
How do they Work?
Differentiate Anodic and Cathodic areas with
indicating solutions
– Anodic Areas – Potassium Ferricyanide
Turns Bluish Green in the presence of Fe++
– Cathodic Areas – Phenolphthalein
Turns bright pink or crimson as pH increases (OH-)
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Corrosion Cells
On-Screen projection to show effects
Anodic
Component
Cathodic
Component
Porous Sponge
Acrylic CellCenter Divider
Connecting
Wire