This document provides an overview of cathodic protection concepts including: - The four elements that create a galvanic corrosion cell and the polarization process that occurs. - How coating characteristics can affect polarization rates. - Common methods for measuring structure-to-electrolyte potentials and criteria for determining effective cathodic protection. - Types of reference electrodes used for measurements, including the copper-copper sulfate electrode. The summary discusses key aspects of cathodic protection and how polarization reduces the potential difference between anodes and cathodes to stop the corrosion reaction.

1. NACE International, 10,000
Lakes Pipeline Corrosion
Control Seminar
BASIC CORROSION SERIES, ROOM C
TUESDAY, FEBRUARY 4, 2020
Advanced Cathodic Protection, 2:00PM – 2:50PM
Eric Langelund
Piping & Corrosion Specialties, Inc.

2. Main Objectives
 Understanding of the Corrosion Process and
the Units of Measure
 The natural process of Corrosion
 The four elements of the Corrosion process
 Ohms Law
 What is the Polarization Process?
 Electrical and Chemical Process
 How do we know, if we are being Cathodically
Protected?
 Measurements methodology
 Equipment Used

3. Definition of Corrosion
 Defined as the electrical chemical
degradation of metal as a result of a
reaction with its surrounding environment
 The tendency of the metal to return to its
natural state

4. The Natural Process of Corrosion
Iron Ore is electrically charged through the molding process.
Once formed into a pipeline, and placed into the ground, the pipe will
lose it’s electrical charge and try to resort back to it’s natural state.
IRON OXIDE BLAST FURNACE BESSEMER
PIPE MILL STEEL PIPE
PIPE CORRODING
IRON OXIDE
REFINING PROCESS
CORROSION PROCESS

5.  The Basic Four Elements to create a galvanic
corrosion cell
 Anode – on the galvanic series charts, the metal
that is the most negative charged and less noble
(The area were corrosion will occur)
 Cathode – on the galvanic series charts, the metal
that is the most positive charged and more noble
(The area that will be cathodically protected)
 Electrolyte – any substance that can conduct
electricity, the surrounding environment of the
anode and the cathode
 Metallic Connection – any metallic connection
between the anode and the cathode that exist
The Electrical Chemical Process of
Corrosion

6.  Conventional Current Flow
 Known as the flow of electrical current for design
and theory purpose
 Where current will flow from the “+” to “-” direction
 Electron Flow
 Contribute to ion movement
 The movement of the electrons from the “-” to the
“+” direction
 Opposite of Conventional Current Flow
The Electrical-Chemical Process of
Corrosion

7.  Corrosion rate can be measured by the
potential difference between the Anode and
the Cathode
 The greater of the potential difference, the
greater of the corrosion rate between the
Anode and the Cathode
 For an example,
 If the anode is measured at -1.700 V and the
cathode is measured at -.600 V
 The potential difference is equal to 1.100 V or 1100
milivolts
The Electrical-Chemical Process of
Corrosion

8. The Electrical-Chemical Process of
Corrosion
Cathode Anode
Positive Negative
Metallic connection
Electrolyte
Conventional
Current Flow
(positive)”+”
to
(negative)”-”
Corrosion
Golden Rule
Any time
Current
discharge
from a
metallic
surface, then
metal loss will
occur
(Corrosion)
-.600 V -1.700 V

9. The Electrical-Chemical Process of
Corrosion
Cathode Anode
Positive Negative
Metallic connection
Electrolyte
Electron Flow
HO-
Electron Flow
(negative)”-”
to
(positive)”+”
HO-
HO-
HO-
H+
H+
H+
H+
H2O
H2O
H2O
e-
e-
e-e-
e-
e-
e-
Fe+
Fe+
Fe+
Fe+
Fe+
-.600 V -1.700 V
H2O (water molecule)

10. The Electrical-Chemical Process of
Corrosion
Cathode Anode
Positive Negative
Metallic connection
Electrolyte
Electron Flow
HO-
HO-
HO-
HO-
H+
H+
H+
H+
H2O
H2O
H2O
e-
e-
e-e-
e-
e-
e-
Fe+
Fe+
Fe+
Fe+
Fe+
As the Cathode
gains the “e-”
(electrons), it
approaches to a
more negative
state
-1.000 V
-
+

11. The Electrical-Chemical Process of
Corrosion
Cathode Anode
Positive Negative
Metallic connection
Electrolyte
Electron Flow
HO-
HO-
HO-
HO-
H+
H+
H+
H+
H2O
H2O
H2O
e-
e-
e-e-
e-
e-
e-
Fe+
Fe+
Fe+
Fe+
Fe+
As the Anode
loses the “e-”
(electrons), it
approaches to a
more positive state
-1.200 V
-
+

12. The Electrical-Chemical Process of
Corrosion
Cathode Anode
Positive Negative
Metallic connection
Electrolyte
Electron Flow
HO-
HO-
HO-
HO-
H+
H+
H+
H+
H2O
H2O
H2O
e-
e-
e-e-
e-
e-
e-
Fe+
Fe+
Fe+
Fe+
Fe+
-1.200 V-1.000 V =
Polarization
Process
The Cathode
becomes more
Negative
The Anode
becomes more
positive

13. Polarization Process
Cathode Anode
Positive Negative
Electrolyte
Electron Flow
HO-
HO-
HO-
HO-
H+
H+
H+
H+
H2O
H2O
H2O
e-
e-
e-e-
e-
e-
e-
Fe+
Fe+
Fe+
Fe+
Fe+
-1.200 V-1.000 V =
Now, what is
the potential
difference ?

14. Polarization Process
 Remember –
 Corrosion rate can be measured by the potential
difference between the Anode and the Cathode
 The greater of the potential difference, the greater
of the corrosion rate between the Anode and the
Cathode
 Earlier example,
 If the anode is measured at -1.700 V and the
cathode is measured at -.600 V
 The potential difference is equal to 1.100 V or 1100
milivolts

15. Polarization Process
 Earlier example,
 If the anode is measured at -1.700 V and the cathode is
measured at -.600 V
 The potential difference is equal to 1.100 V or 1100 milivolts
 Now,
 The anode is measured at -1.200 V and the cathode is
measured at -1.000 V
 The potential difference is equal to .200 V or 200 milivolts
 Conclusion –
 Polarization will reduce the rate of corrosion on the anode
over time as the Cathode and the Anode approach an equal
potential, due to the loss and gain of electrons

16. Polarization Review - Diagram

17. The “True Criterion” for Cathodic
Protection
 Polarization of the Cathodes to the open
circuit potential to the anodes is the true
criterion for cathodic protection (stopping
the corrosion reaction)

18. How are Polarization rates affected
by Coating Characteristics
 Bare Pipe
 Will polarize and de-polarize quickly due to
larger bare metallic surface area
 Well - Coated Pipe
 Will polarize and de-polarize slowly due to a
much smaller bare metallic surface area

19. How are Polarization rates affected
by Coating Characteristics
Holiday
CP only protects the coating defected areas or best
known as holidays (bare area of the well coated pipeline)

20. Current Measurement - CP
 The following Current density is
considered
 Good soil (moist all year round) or fresh water – 1
mA sq ft
 Clay (partially moist soil) – 2 mA to 3 mA sq ft
 Sandy or Dry soils – 4 mA to 8 mA sq ft

21.  For an example –
Current Measurement - CP
6” coated pipeline at a 12,000’ length with .5% coating
defect.
.005 • 20,820 sq ft (total surface area) = 104.1 sq ft of bare
area A = 104.1 sq ft
i = 1 mA per sq ft
.001 • 104.1 = .104Amps or 104mA
Answer for I is 104mA If bare pipe was used then the
current requirement would be much
greater, in the range of 21 amps vs.
.1 of an amp

22.  In Summary,
 The bare pipe will take a large amount of CP
current to cathodically protect
 Polarization will take longer to achieved
 Therefore, the depolarization will be longer as well
 The well coated pipeline will take much less of CP
current to cathodically protect
 Polarization will be quicker to achieved
 Therefore, the depolarization will be quicker as well
Current Measurement - CP

23.  Remember, CP is achieved by polarizing the
Cathode to the open potential of the Anode
 On the surface of the metallic pipeline, a
galvanic corrosion cell can form with the
following criteria’s
 Anodic area (high negative potential),
 Cathodic area (Low negative potential or more
positive potential),
 Metallic connection (pipeline structure)
 Electrolyte (surrounding environment)
Polarization reduces VΔ along the
Structure

24. Galvanic Corrosion Cell on
Pipelines
AnodeCathode
Microscopic Corrosion Cell
on the Surface of a
Pipeline Remember the golden
rule of Corrosion – @
the point of current
discharge, metal loss
will occur (Corrosion)

25.  Applying CP currents to the surface
 We attempt to create the same potential
between the anode and the cathode
 If No potential difference exist, then there is
no driving force for the electrons to move, in
which will result in stopping metal discharge
(corrosion)
 Let’s look at this process closer
Polarization reduces VΔ along the
Structure

26. -.5 -.6 -.65 -.6 -.7 -.58
-.58 -.6 -.65 -.6 -.7 -.58
-.6 -.6 -.65 -.6 -.7 -.6
-.65 -.65 -.65 -.65 -.7 -.65
-.7 -.7 -.7 -.7 -.7 -.7
Static
Potentials
Corrosion
Mitigated
P
O
L
A
R
I
Z
A
T
I
O
N
Polarization reduces VΔ along the
Structure
Once the surface area has polarized to the same potential,
there is no “Anode” or “Cathode”, Cathodic Protection is
achieved.
1. Static Potential
2. Most positive sides
polarize first
3. Next most positive
sites polarize
4. Last most positive
site polarize
5. All sites polarized

27. How do we know, if we are being
Cathodically Protected?
 Structure to electrolyte potential
 Typically made at grade
 Voltmeter and reference electrode
 High input impedance voltmeter
 Compare potentials measured to
“criteria”

28. Pipe to Soil Potential Measurements
-.900 v
+_
Polarization Film
Reference Electrode

29. Voltmeters
 Analog vs. Digital
 High Input Impedance
 Field Durable
 Storage Capabilities

30. Voltmeter identifies More Noble
Metals
 If a voltmeter is connected such that
 the positive terminal is to the more noble
 metal and the negative terminal to the
 more active metal, the reading is
positive.

31. Noble Active
+ _
Voltage
measurement
is positive
.600 V
Voltmeter identifies More Noble
Metals

32. Pipe-to-Soil Potential Measurement
.900 v
+
_
Pipe
Electrolyte
Reference
Cell
Voltmeter Meter display is a
postive reading.
Record a negative
P/S Potential.
-.900 v
+
_
Pipe
Electrolyte
Reference
Cell
Voltmeter Meter display is a
negative reading.
Record a negative
P/S Potential.
Pipe To Soil Measurement
Be aware of the connection of the
leads to indicate a “+” or “-” reading

33. The Common Different Types of
Reference Electrodes
 Calomel
 Libratory use
 Silver/Silver Chloride
 Sea water use
 Zinc
 Sea water use
 Copper-Copper Sulfate
 Regular soil & neutral waters
 Most popular use in the field

34. Most Common for Field Use
 Copper – Copper Sulfate
 Rugged for field use
 Consistent measurements in neutral waters
and soil environments
 Contains
 Copper Rod
 Copper Crystals
 Copper solutions (antifreeze material) or distilled
water

35. Copper Rod
Saturated Copper
Sulfate Solution
Un-dissolved Copper
Sulfate Crystals
Porous
Plug
Visual
Window
Copper – Copper Sulfate
Reference Cell

36. Copper – Copper Sulfate Reference
Cell (Half Cell)
Cathode Anode
Positive Negative
Electrolyte
Copper-
Copper
Sulfate
reference
cell
Steel
Pipeline
Test station wire
The copper –
copper sulfate
reference cell
represents half of
the corrosion
cell, therefore
gets the name
“Half Cell”

37. Care of the CSE
 Keep the CSE clean
 Keep the cap on the tip to prevent dryness and
cracking or loss of solution
 Keep free of contamination, the tip is porous so
therefore, contaminates can pass in the CSE solution
 Perform calibration with a virgin half cell on regular
bases
 Shield clear window from sunlight, due to heat or UV
rays will cause inaccuracy in readings (normally use
black electrical tape)
 Adjust readings according to temperature

38. Criteria’s of CP
 .850- V CSE with current applied (IR
drop consideration)
 .850- V CSE Polarized (Instant off)
 100 mV Polarization decay

39. Criteria - .850– V CSE with Current
Applied
 Structure to electrolyte potential with a high
impedance volt meter and copper-copper
sulfate reference cell
 IR drop is considered by
 Placing the reference cell directly over the pipeline
as possible
 As close to the pipeline as possible
 Eliminating the resistance at the point of the
reference cell contact as much as possible
 Wetting the soil
 Removing the sod

40. Criteria - .850 – V CSE Polarization
 Structure to electrolyte potential with a
high impedance volt meter and copper-
copper sulfate reference cell
 Switching off the CP currents
 Measure the IR drop
 @ the point of polarization decay begins,
reading is used for criteria

41. Criteria - .850 – V CSE Polarization

42. Criteria – 100 mV Polarization
Decay
 Structure to electrolyte potential with a
high impedance volt meter and copper-
copper sulfate reference cell
 Switching off the CP currents
 Measure the IR drop (instant off)
 @ the point of polarization decay,
measure until 100 mV depolarization has
been achieved

43. Criteria – 100 mV Polarization
Decay

44. Summary
 Corrosion is the degradation of a material due
to a reaction with its’ environment
 CP is achieved when the cathodic sites are
polarized in the electronegative direction to the
potential of the most anodic sites.
 Only practical method to determine this is by
surface structure to electrolyte potentials

50. PIPELINE INSTALLATION

51. ANODE INSTALLATION

52. RECTIFIER

53. REMOTE MONITORING

54. DAGB

55. CONSUMED ANODE

56. CONVENTIONAL GROUNDBED

57. REVERSE CURRENT SWITCH

58. DRAINAGE SWITCH

59. PETROLEUM PIPE SPAN

60. ANODE IN HOLE

61. ANODES AROUND UST

62. WATER VALVE REPAIR

63. ANODE INSTALLATION

64. GRAPHITIZATION

65. PCCP

66. COPPER

67. CONTINUITY BOND

68. CONTINUITY BOND

69. CI and DI WALL
THICKNESS

70. REBAR COATED

71. DAMAGED COATING

72. DAMAGED COATING

73. POLYETHELENE

74. CONTINUITY BONDS

75. SAFETY FIRST

76. THANK YOU
 CATHOLIC PROTECTION
76