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Jeff SchramukNACE CP Specialist #7695
www.cpsolutionsinc.net
Basic CorrosionBasic Corrosion
andandCathodic ProtectionCathodic Protection
Basic Corrosion & Cathodic Protection
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Topics to be Covered
Why Should We Be Concerned about Corrosion?
Definitions and Terminology
Forms of Corrosion
Pipe Coatings and Cathodic Protection
Cathodic Protection using Magnesium Anodes
Advantages & Limitations of Galvanic Anode CP Systems
Impressed Current Cathodic Protection
Measurement and Testing of CP Systems
Field Test Equipment
Cathodic Protection Criteria.
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Why Should We Be Concerned about Corrosion?
Definitions and Terminology
Forms of Corrosion
Pipe Coatings and Cathodic Protection
Cathodic Protection using Magnesium Anodes
Advantages & Limitations of Galvanic Anode CP Systems
Impressed Current Cathodic Protection
Measurement and Testing of CP Systems
Field Test EquipmentCathodic Protection Criteria.
Basic Corrosion & Cathodic Protection
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Effects of Infrastructure Corrosion
Life Safety
Economics Environmental
Regulatory
Compliance
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Why Should We Be Concerned about Corrosion?
Definitions and Terminology
Forms of Corrosion
Pipe Coatings and Cathodic Protection
Cathodic Protection using Magnesium Anodes
Advantages & Limitations of Galvanic Anode CP Systems
Impressed Current Cathodic Protection
Measurement and Testing of CP Systems
Field Test EquipmentCathodic Protection Criteria.
Basic Corrosion & Cathodic Protection
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Corrosion Can be Defined as:
Practical
Definition
Scientific
Definition
The Tendencyof a Metal to
Revert to its
Native State
Electrochemical
Degradation of Metal
as a Result of aReaction with its
Environment
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Corrosion - A Natural Process
IRON OXIDE REFINING MILLING
IRON CORROSION IRON OXIDE
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Four Basic Parts of a Corrosion Cell
Anode A metal electrode in contact with the
electrolyte which corrodes
Cathode - A metal electrode in contact with the
electrolyte which is protected against corrosion
Electrolyte A solution or conducting medium
such as soil, water or concrete which contains
oxygen and dissolved chemicals
Metal Path An external circuit that connects
the anode and the cathode
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Electron Flow vs. Conventional Current
Flow of conventional current is from positive (+) tonegative (-)
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.
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Anodic Area
(Metal Loss)
DC Current
Cathodic
Area
(Protected)
Definitions - Anodes & Cathodes
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Copperat-2
00mV
Steelat-600mV
The Simplified Corrosion Cell
Cop
perat-200m
V
Ste
elat-600mV
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-
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Material Potential*Pure Magnesium -1.75Magnesium Alloy -1.60Zinc -1.10Aluminum Alloy -1.00
Mild Steel (New) -0.70Mild Steel (Old) -0.50Cast / Ductile Iron -0.50Stainless Steel -0.50 to + 0.10Copper, Brass, Bronze -0.20
Gold +0.20Carbon, Graphite, Coke +0.40
* Potentials With Respect to Saturated Cu-CuSO4 Electrode
L
ess
Active
More
Practical Galvanic Series*
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Corrosion Reaction and Ohms Law
Ohms 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)
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Some Common Electrical Quantities
Current Flow: 1 ampere (A) = 1000 milliamps (mA)
Examples:
A sacrificial anodes output is measured in mA
A CP rectifiers output is can be up 100 A
Voltage: 1 volt (V) = 1000 millivolts (mV)
Examples:
A magnesium anodes potential is ~1.6 V (1600 mV)
A CP rectifier can have a DC voltage of up to 100 V
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Corrosion Cell - Anodic Reactions
Copperat-200mV
Steelat-60
0mV
Cathode
AnodeI
e-Fe++
Fe++
Fe++
OH-
OH-
OH-
I
I
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Corrosion Cell - Cathodic Reactions
Copperat-20
0mV
Steelat-60
0mV
Cathode
Anode
I
e-H+
H+
H+
H+
e-
e-
e-
e-
I
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Corrosion Cell Combined Reactions
Copperat-20
0mV
Steelat-600mV
Cathode
Anode
I
e-H2
H2
e-
H2
H2
Fe2(OH)3
Fe2(OH)3
Fe2(OH)3
I
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Why Should We Be Concerned about Corrosion?
Definitions and Terminology
Forms of Corrosion
Pipe Coatings and Cathodic Protection
Cathodic Protection using Magnesium Anodes
Advantages & Limitations of Galvanic Anode CP Systems
Impressed Current Cathodic Protection
Measurement and Testing of CP Systems
Field Test EquipmentCathodic Protection Criteria.
Basic Corrosion & Cathodic Protection
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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
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True Uniform Corrosive Attack
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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
metals
Area Effect
Avoid small anode connected to a large cathode
Distance Effect
Area closest to anode will have the greatest corrosion
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Material Potential*Pure Magnesium -1.75Magnesium Alloy -1.60Zinc -1.10Aluminum Alloy -1.00
Mild Steel (New) -0.70Mild Steel (Old) -0.50Cast / Ductile Iron -0.50Stainless Steel -0.50 to + 0.10Copper, Brass, Bronze -0.20
Gold +0.20Carbon, Graphite, Coke +0.40
* Potentials With Respect to Saturated Cu-CuSO4 Electrode
Less
Active
More
Practical Galvanic Series*
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Galvanic Corrosion Bimetallic Connection
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Old Pipe(Cathode)
New Pipe(Anode)
Old-New Pipe Corrosion Cell
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Steel in Concrete-Soil
Cathodic
ZoneAnodic
Zone
Concrete
Encasement
Pipe in Soil
Corrodes
Note: Arrows Indicate Direction of DC Current Flow
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Dissimilar Surface Conditions
Pipe(Cathode) Threads
Bright Metal
(Anode)
Scratches(Anode)
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Concentration Cell Corrosion
Due to differences in the environment
Differential Soil Aeration Very common
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Aerated Soil
Differential Soil Aeration
Oxygen diffusing throughbackfill sustains corrosion tocathodic (top) area of pipe
Lack of oxygen at bottom ofpipe creates relative corrosioncell to (top) area of pipe
Clay soil Clay soil
Anodic Zone
Cathodic Zone
O2 O2
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Differential Aeration on Cast Iron Pipe
Cathodic Zone
Anodic Zone
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Clay (moistlow 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)
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Pitting of Coated Carbon Steel in Soil
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External Pitting: Ductile Iron Water Main
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Selective Leaching Corrosion
Selective LeachingGraphitization (Gray Cast Iron)
Dezincification (Brass)
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Dealloying Corrosion (Graphitization)
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Why Should We Be Concerned about Corrosion?
Definitions and TerminologyForms of Corrosion
Pipe Coatings and Cathodic Protection
Cathodic Protection using Magnesium Anodes
Advantages & Limitations of Galvanic Anode CP Systems
Impressed Current Cathodic Protection
Measurement and Testing of CP Systems
Field Test EquipmentCathodic Protection Criteria.
Basic Corrosion & Cathodic Protection
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Eliminating the Corrosion Cell
Anode
Cathode
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Apply a Bonded Tape Wrapping
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Pitting at a Coating Defect
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Coat the Structure & Electrically Isolate It
Whats WrongHere?
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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 Corrosion
Pipe Coatings and Cathodic Protection
Cathodic Protection using Magnesium Anodes
Advantages & Limitations of Galvanic Anode CP Systems
Impressed Current Cathodic Protection
Measurement and Testing of CP Systems
Field Test EquipmentCathodic Protection Criteria.
Basic Corrosion & Cathodic Protection
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Corrosion occurs where current dischargesfrom metal to electrolyte
The objective of cathodic protection is toforce the entire surface to be cathodic to the
environment.
How Cathodic Protection Works
G l i A d C th di P t ti
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Current is obtained from a metal of a higher
energy level.
Galvanic Anode Cathodic Protection
P ti l G l i S i *
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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 -0.20
Gold +0.20Carbon, Graphite, Coke +0.40
* Potentials With Respect to Saturated Cu-CuSO4 Electrode
Less
Active
More
Practical Galvanic Series*
Gal anic Corrosion No C P Benefit
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Copper-200mV
Steel-600mV
Magnesium
-1.7V
1. Anode2. Cathode
3. Electrolyte
4. Metal Path
Galvanic Corrosion No C.P. Benefit
Galvanic Corrosion Mitigated w/CP
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Cath
ode
Cathode
Anode
1. Anode
2. Cathode
3. Electrolyte
4. Metal Path
Galvanic Corrosion - Mitigated w/CP
CP Performance Can Be Verified
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CP Performance - Can Be Verified
Sacrificial Anode on a Buried Pipeline
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Sacrificial Anode on a Buried Pipeline
Sacrificial Anode
CoatingDefect
Connection to Pipe
Grade
Sacrificial Anode w/Test Station
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CoatingDefect
Connection to Pipe
Grade
Sacrificial Anode
Sacrificial Anode w/Test Station
CP Test Station - Terminal Board
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CP Test Station - Terminal Board
structurelead wireanodelead wire
insulated
terminal board calibratedshunt resistor
Magnesium Anodes
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Magnesium Anodes
Packaged Magnesium Anode
N l G PL
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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 dont lift by the lead wire
Tamp earth firmly around anode package.
Natural Gas PL
Packaged Magnesium Anode
N t l G PL ( t )
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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.
Natural Gas PL (cont.)
Packaged Magnesium Anode
N t l G PL ( t )
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Natural Gas PL (cont.)
*Detail courtesy of Midwest Energy Association*Detail courtesy of Midwest Energy Association
Basic Corrosion & Cathodic Protection
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Why Should We Be Concerned about Corrosion?
Definitions and TerminologyForms of Corrosion
Pipe Coatings and Cathodic Protection
Cathodic Protection using Magnesium Anodes
Advantages & Limitations of Galvanic Anode CP Systems
Impressed Current Cathodic Protection
Measurement and Testing of CP Systems
Field Test Equipment
Cathodic Protection Criteria.
Basic Corrosion & Cathodic Protection
Galvanic Anode CP Advantages
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No external AC power is requiredEffective utilization of protective current
Simple and inexpensive to install on newunderground structures
Seldom cause stray DC interferenceMinimal maintenance requirements.
Galvanic Anode CP Limitations
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Limited driving potential
E = (Ea Ec)Limited current output I = E / Rt
Large number of anodes will be required onbare or poorly coated structures
Ineffective in high-resistivity soilenvironments (Rt ).
Basic Corrosion & Cathodic Protection
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Why Should We Be Concerned about Corrosion?
Definitions and TerminologyForms of Corrosion
Pipe Coatings and Cathodic Protection
Cathodic Protection using Magnesium Anodes
Advantages & Limitations of Galvanic Anode CP Systems
Impressed Current Cathodic Protection
Measurement and Testing of CP Systems
Field Test Equipment
Cathodic Protection Criteria.
Basic Corrosion & Cathodic Protection
Surface (Horizontal) Anode System
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Rectifier
AnodeGroundbed
( - ) ( + )
Pipeline
(Structure)
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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Basic Corrosion & Cathodic Protection
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Why Should We Be Concerned about Corrosion?
Definitions and TerminologyForms of Corrosion
Pipe Coatings and Cathodic Protection
Cathodic Protection using Magnesium Anodes
Advantages & Limitations of Galvanic Anode CP Systems
Impressed Current Cathodic Protection
Measurement and Testing of CP Systems
Field Test Equipment
Cathodic Protection Criteria.
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
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Reference Cells
Test Station
Voltmeter-Computer
Wire Dispenser &Distance Chainer
Pipeline
Basic Corrosion & Cathodic Protection
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Why Should We Be Concerned about Corrosion?
Definitions and Terminology
Forms of Corrosion
Pipe Coatings and Cathodic Protection
Cathodic Protection using Magnesium Anodes
Advantages & Limitations of Galvanic Anode CP SystemsImpressed Current Cathodic Protection
Measurement and Testing of CP Systems
Field Test Equipment
Cathodic Protection Criteria.
CP Test Equipment - Multi-Meters
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Multi-Meter Characteristics
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Basic Functions
Reads AC & DC Volts
Reads Ohms (optional diode checker)
Reads AC and DC Amps (be careful here!)Performance Criteria
Field rugged, water/drop resistant
High input impedance (min. 20 M-)
Test Equipment Quality Assurance
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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
Reference Electrode Basic Components
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Reference Electrode - Maintenance
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Periodically verify cell against a known standard
Keep porous plug covered when not used
Clean and refill the reference cell annually
Clean copper rod with a non-metallic abrasive pad
Replace w/fresh Cu/CuSO4 solution ( full at all times)
Some Cu/CuSO4 crystals should always remain in
suspension
Wash hands after using Cu/CuSO4 solution is
hazardous
P/S Potential Readings
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Connect voltmeter to pipe and reference
Ensure reference cell plug has good contact with moist
soil not pavement
Place reference cell away from anodesRead P/S on DCV scale
Record P/S reading using standard forms
If polarity is positive, notify corrosion dept.
Meter Connections
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Basic Corrosion & Cathodic Protection
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Why Should We Be Concerned about Corrosion?
Definitions and Terminology
Forms of Corrosion
Pipe Coatings and Cathodic Protection
Cathodic Protection using Magnesium Anodes
Advantages & Limitations of Galvanic Anode CP SystemsImpressed Current Cathodic Protection
Measurement and Testing of CP Systems
Field Test Equipment
Cathodic Protection Criteria.
DOT Standard Part 192.463
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Cathodic Protection Criteria-0.85 V (w/IR-drop consideration)
-0.85 V Instant-Off
100 mV polarization decay
Other criteria determined to be appropriate by
regulatory authority
NACE International CP Criteria
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DOT Standard Part 192.465
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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.
Do We Have a Good Reading?
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