Unformatted text preview: CP Interference January 2008
©NACE International, 2006 IMPORTANT NOTICE
Neither the NACE International, its officers, directors, nor members thereof accept
any responsibility for the use of the methods and materials discussed herein. No
authorization is implied concerning the use of patented or copyrighted material.
The information is advisory only and the use of the materials and methods is
solely at the risk of the user.
It is the responsibility of the each person to be aware of current local, state and
federal regulations. This course is not intended to provide comprehensive
coverage of regulations.
Printed in the United States. All rights reserved. Reproduction of contents in
whole or part or transfer into electronic or photographic storage without
permission of copyright owner is expressly forbidden. Acknowledgements
The scope, desired learning outcomes and performance criteria of this course were
developed by the CP Task Group under the auspices of the NACE Education
Administrative Committee.
The time and expertise of several members of NACE International have gone into the
development of this course—and its task analysis, course outline, student manual,
classroom lab manual, presentation slides, and examinations. Their dedication and efforts
are greatly appreciated.
On behalf of NACE, we would like to thank the task group for its work. Their efforts
were extraordinary and their goal was in the best interest of public service—to develop
and provide a much needed training program that would help improve corrosion control
efforts industry-wide. We also wish to thank their employers for being generously
supportive of the substantial work and personal time that the members dedicated to this
program. CP Interference Course Development Task Group
Paul Nichols, Task Group Chairman
Brian Holtsbaum
Kevin Parker
David A. Schramm
Steven R. Zurbuchen
Steven Nelson
Donald R. Mayfield Shell Global Solutions, Houston, Texas
CC Technologies Canada, Ltd., Calgary,
Alberta
CC Technologies, Mt. Pleasant, Michigan
EN Engineering, Woodridge, Illinois
EN Engineering, Topeka, Kansas
Columbia Gas Transmission, Charleston,
West Virginia
Dominion
Transmission,
Delmont,
Pennsylvania CP Interference
Daily Course Outline
DAY ONE
Introduction, Welcome, Overview
Chapter 1 Stray Current Interference DAY TWO
Chapter 2 DC Interference
(Includes Experiment 2-1) DAY THREE
MORNING
Chapter 2 DC Interference AFTERNOON
Chapter 3 AC Interference
(Includes experiments 3-1, 3-2, and 3-3) DAY FOUR
Chapter 3 AC Interference DAY FIVE
MORNING
Chapter 3 AC Interference AFTERNOON
Chapter 4 Telluric Current Interference DAY SIX
MORNING
Exam CP Interference Course Manual
© NACE International, 2006
January 2007 Introduction Introduction
The Cathodic Protection (CP) Interference course is a six-day course
focusing on alternating current (AC) and direct current (DC)
interference. The course includes in-depth coverage of both the
theoretical concepts and the practical application of identifying
interference and interference mitigation techniques. Students will
learn to identify the causes and effects of interference as well as
conduct tests to determine if an interference condition exists and
perform calculations required to predict AC interference. The course
is presented in a format of lecture, discussion and hands-on, in-class
experiments, case studies and group exercises. There is a written
examination at the conclusion of the course. Who Should Attend
This course is designed for persons who have extensive CP field
experience, a strong background in mathematics, and a strong
technical background in CP. Prerequisites
• CP 3–Cathodic Protection Technologist certification
recommended
• Minimum of 3 years CP work experience Length
The course begins at 1 p.m. on Sunday and concludes Friday
afternoon.
Daily class hours: 8 a.m. to 6:30 p.m. Monday through Thursday and
8 a.m. to 3 p.m. Friday. Reference Book
Students will receive the CP Interference Course Manual prior to the
start of the course. A course manual on CD-ROM will be provided
to students on-site.
CP Interference Course Manual © NACE International, 2006
July 2007 1 Introduction Quizzes and Examinations
There will be four (4) quizzes distributed during the week and
reviewed in class by the instructors.
This course has a written final examination. The final examinations
will be given on Friday.
The written final examination is open-book and students may bring
reference materials and notes into the examination room.
Non-communicating,
battery-operated,
silent,
non-printing
calculators, including calculators with alphanumeric keypads, are
permitted for use during the examination. Calculating and computing
devices having a QWERTY keypad arrangement similar to a
typewriter or keyboard are not permitted. Such devices include but are
not limited to palmtop, laptop, handheld, and desktop computers,
calculators, databanks, data collectors, and organizers. Also excluded
for use during the examination are communication devices such as
pagers and cell phones along with cameras and recorders.
A score of 70% or greater on the examination is required for
successful completion of the course. All questions are from the
concepts discussed in this training manual.
You will receive written notification of your exam results as quickly
as possible. Your results will not be available on Friday. Introductions
We would like for each of you to stand, one at a time and introduce
yourself to the class. Tell us:
• Your name • Your company’s name and location • Your job function • Your experience related to CP Interference. CP Interference Course Manual © NACE International, 2006
July 2007 2 CP Interference
Course Manual
Table of Contents
General Course Information
Daily Course Outline
Introduction
Chapter 1–Stray Current Interference
1.1 Historical Background ........................................................... 1:1 1.2 Typical Stray Current Circuit Arising from a Transit
System Operation ................................................................. 1:5 1.3 Stray Current Charge Transfer Reactions on a.....................
Metallic Structure 1:6 1.4 Effects of Stray Current on Metallic Structures ..................... 1:9 1.4.1
1.4.2
1.4.3 At the Current Discharge Location......................................
At Area of Current Pick-Up .................................................
Along the Structure ............................................................. 1:9
1:15
1:19 1.5 Summary .............................................................................. 1:21 Summary of Equations.................................................................. 1:22 Figures
Fig. 1-1
Fig. 1-2
Fig. 1-3
Fig. 1-4
Fig. 1-5
Fig. 1-6 Early Electric Trolley..............................................................
Pipe-to-soil Potential Changes due to Transit System
Stray Current Activity were Recorded on Smoked Charts..
Co-efficient of Corrosion at Different Frequencies for
Iron Electrode Denoted as Average Electrode Loss...........
Typical Stray Current Paths Around a DC Transit System ....
Typical Stray Current Interference on a Metallic
Underground Structure .......................................................
Simplified pH Pourbaix Diagram For Iron in Water at 25ºC
Showing Potential Shift Direction for Current Pick-up
and Discharge at Low pH ................................................... CP Interference Course Manual
© NACE International, 2006
June 2007 1:1
1:3
1:4
1:6
1:6
1:8 Fig. 1-7
Fig. 1-8
Fig. 1-9
Fig. 1-10
Fig. 1-11
Fig. 1-12
Fig. 1-13
Fig. 1-14
Fig. 1-15a
Fig. 1-15b
Fig. 1-16 Simplified pH Pourbaix Diagram For Iron in Water at 25ºC
Showing Potential Shift Direction for Current Pick-up
and Discharge at High pH...................................................
Current Discharge from a Metal Structure to Earth via
an Oxidation Reaction ........................................................
Superposition of a Stray Current and a Cathodic Protection
Current at a Metal/Electrolyte Interface ..............................
Randle’s Electrical Circuit Model of a Metal/Electrolyte
Interface..............................................................................
Theoretical Conditions of Corrosion, Immunity and
Passivation of (a) Aluminum at 25ºC and
(b) Lead at 25ºC .................................................................
Comparison of Zn and Al Coatings for Corrosion
Resistance as Functions of pH ...........................................
Typical Section Through a Joint in Two Types of PCCP .......
Cathodic Blistering/Disbondment of Protective Coating ........
Stray Current Discharge and Pick-Up Around an
Electrically Discontinuous Joint Though the Earth..............
Stray Current Discharge and Pick-Up Through the
Internal Aqueous Medium Around an Electrically
Discontinuous Bell and Spigot Joint on Cast Iron Piping....
Stray Current Circuit in an AC Electrical Distribution
System................................................................................ 1:9
1:10
1:10
1:14
1:16
1:17
1:18
1:19
1:19
1:20
1:20 Tables
Table 1-1 Theoretical Consumption Rates of Various Metals and
Substances .................................................................. 1:12 Table 1-2 Electrochemical and Current Density Equivalence with
Corrosion Rate.................................................................... 1:13 Chapter 2–DC Interference
2.1 Introduction ........................................................................... 2:1 2.2 Detecting Stray Current ........................................................
2:23
2.2.1 Mitigation of Interference Effects from Impressed Current
Cathodic Protection Systems .....................................
2:24
a. Source Removal or Output Reduction ..........................
2:25
b. Installation of Isolating Fittings......................................
2:26
c. Burying a Metallic Shield Next to the Interfered-with
Structure ....................................................................
2:27
d. Installation of Galvanic Anodes on Interfered-with
Structure at Point of Stray Current Discharge............
2:28
e. Installation of an Impressed Current Distribution System
on the Interfered-with Structure at Point of Stray Current
Discharge...................................................................
2:33
f. i. Installing a Bond Between the Interfered-with and CP Interference Course Manual
© NACE International, 2006
June 2007 Interfering Structures................................................
ii. Calculation of Bond Resistance ...............................
g. Use of Coatings in the Mitigation of Interference Effects
2.2.2 2:33
2:35
2:40 Other Sources of DC Stray Current ....................................
2:41
a. DC Transit Systems ......................................................
2:42
i. Analysis of Transit System Stray Currents ...............
2:44
ii. Mitigation of Transit System Stray Currents .............
2:51
b. High Voltage Direct Current (HVDC) Electrical Transmission
Systems .....................................................................
2:55
c. DC Welding Operations ................................................
2:57 Experiment 2-1: To Demonstrate DC Interference
and Its Mitigation........................................................ 2:59 ………………………………………………………. ….. 2.64 Summary of Equations ............................................................................ 2:65 Case Study Figures
Fig. 2-1
Fig. 2-2
Fig. 2-3
Fig. 2-4
Fig. 2-5
Fig. 2-6
Fig. 2-7a
Fig. 2-7b
Fig. 2-8
Fig. 2-9
Fig. 2-10
Fig. 2-11
Fig. 2-12
Fig. 2-13
Fig. 2-14
Fig. 2-15
Fig. 2-16 Parallel Current Paths in the Earth ....................................
Parallel Current Paths in a Pipeline Cathodic Protection
Section................................................................................
Parallel Current Paths in Vertically Stratified Soil Conditions
Parallel Current Paths in Horizontally Stratified Soil
Conditions...........................................................................
Polarization Test Results.......................................................
Stray Current in a Metallic Structure Parallel to a
Cathodically Protected Structure ........................................
Voltage vs. Distance from a Vertically Oriented Anode .........
Multiple Vertical Anodes Connected to a Common
Header Cable .....................................................................
Multiple Horizontal Anodes Connected to a Common
Header Cable .....................................................................
Hemispherical Electrode........................................................
Cathodic Protection Circuit Model with Foreign Structure
Intercepting the Anode Gradient.........................................
Potential Profile along the Interfered-with Structure ..............
Electrical Model for Interfered-with Pipe ................................
Attenuation Model..................................................................
Voltage Gradient in the Earth Around a Cathodically
Protected Bare Pipeline ......................................................
Cathodic Protection Circuit Model .........................................
Cathodic Protection Circuit Model with Foreign Structure
Intercepting the Anode Gradient.........................................
Stray Current in a Foreign Metallic Structure that Intercepts
both the Anodic and Cathodic Voltage Gradient................. CP Interference Course Manual
© NACE International, 2006
June 2007 2:1
2:2
2:3
2:3
4:5
2:5
2:6
2:7
2:8
2:9
2:11
2:14
2:14
2:15
2:18
2:18
2:19
2:20 Fig. 2-17 Cathodic Protection Circuit Model with Foreign Structure
Intercepting both Anodic and Cathodic Voltage Gradient...
Fig. 2-18 Stray Current in a Foreign Metallic Structure that Intercepts
the Cathodic Protection Gradient........................................
Fig. 2-19 Cathodic Protection Circuit Model for Foreign Structure
Intercepting the Cathodic Voltage Gradient........................
Fig. 2:20 Typical Potential Profile on an Interfered-with Structure
that Intersects both Anodic and Cathodic Voltage
Gradient with the Current Source Interrupted.....................
Fig. 2-21 Current Changes In and Near an Interfered-with Structure ...
Fig. 2-22 Stray Current Arising from Installation of Isolating Fittings ....
Fig. 2-23 Using a Buried Metallic Cable or Pipe as a Shield to
Reduce Stray Current Interference.....................................
Fig. 2-24 Cathodic Protection Current Model for a Buried Metallic
Shield Connected to the Negative Terminal of the
Transformer-Rectifier..........................................................
Fig. 2-25 Interference Mitigation using Galvanic Anodes at Stray
Current Discharge Location ................................................
Fig. 2-26 Electrical Circuit Model for Mitigating Stray Current
Interference at a Stray Current Discharge Site Using
Galvanic Anodes.................................................................
Fig. 2-27 Potential Profile Changes on a Pipeline where Stray
Current is Discharging in an End-Wise Pattern ..................
Fig. 2-28 Interference Mitigation Using a Resistance Bond..................
Fig. 2-29 Measurements Required to Determine Size of Resistance
Bond Re ..............................................................................
Fig. 2-30 Use of a Dielectric Coating to Mitigate Interference ..............
Fig. 2-31 Typical Stray Current Paths Around a DC Transit System ....
Fig. 2-32 Typical Structure-to-Soil Potential Recording with Time
Caused by Interference from a DC Transit System ............
Fig. 2-33 Current Clamp Used to Measure Pipeline Currents ..............
Fig. 2-34 Line Current Survey to Locate Source of Interference
Using IR-Drop Test Stations ...............................................
Fig. 2-35 Line Current Plots for Example in Figure 2-34 ......................
Fig. 2-36 Exposure Survey to Locate Point of Maximum Exposure......
Fig. 2-37 Exposure Survey Plots for Example in Figure 2-36 ...............
Fig. 2-38 Mutual Survey to Confirm Source of Interference..................
Fig. 2-39 Pipe-to-Soil Potential Versus Pipe-to-Rail Potential for
Example in Figure 2-38.......................................................
Fig. 2-40 Exposure Survey Conducted Without the Measurement
Of Pipeline Currents ...........................................................
Fig. 2-41 Exposure Survey Plots for Example in Figure 2-40 ...............
Fig. 2-42a Typical Embedded Track Installation.....................................
Fig. 2-42b Typical Direct-Fixation Isolating Fastener .............................
Fig. 2-43 Typical Utilities Drainage System at a Transit Substation .....
Fig. 2-44 Schematic Showing Circulating Current between Transit
Substations Through Direct Bonds to Utilities ....................
Fig. 2-45 Forced Drainage Bonds Using a Potential Controlled
Rectifier...............................................................................
Fig. 2-46 Electrical Schematic for a HVDC System .............................. CP Interference Course Manual
© NACE International, 2006
June 2007 2:20
2:21
2:22
2:23
2:24
2:26
2:27
2:28
2:29
2:30
2:33
2:34
2:36
2:41
2:42
2:43
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2:47
2:48
2:48
2:49
2:50
2:50
2:52
2:52
2:52
2:53
2:54
2:55 Fig. 2-47 Potential-Time Plot for a Metallic Structure being
Interfered-with by a HVDC System.....................................
Fig. 2-48 Stray Current Caused by DC Welding Operations ................ 2:57
2:58 Experiment Schematic No. 1...................................................................
Experiment Schematic No. 2...................................................................
Experiment Schematic No. 3................................................................... 2:59
2:60
2:61 Table 2-1 Specific Leakage Resistances and Conductances in
1000 Ω-cm Soil or Water .......................................................
Table 2-2 Types of Reverse Current Switches ...................................... 2:13
2:54 Tables Chapter 3–AC Interference
3.1 Introduction ...........................................................................
3.1.1
3.1.2
3.1.3 Experiment 3-1: 3:1 Electrostatic (Capacitive) Coupling.....................................
3:2
Electromagnetic (Inductive) Coupling .................................
3:11
Conductive Coupling (Resistive Coupling) During Powerline Fault
Conditions...........................................................................
3:14
To Demonstrate the Effects of Electrostatic
Induction ............................................................................. 3:16 3.2 Basic Theory of Electromagnetically Induced Voltages ........ 3:19 3.2.1
3.2.2
Experiment 3-2: AC Circuit Theory ...............................................................
The Nature of Induced AC Pipeline Voltages ..................... 3:19
3:34 To Demonstrate the Effects of Electromagnetic
Induction ............................................................................. 3:42 3.3 Induced AC Voltages ............................................................ 3:44 3.3.1
3.3.2
Experiment 3-3: Factors that Affect the Longitudinal Electric Field...............
Factors that Affect the Pipeline Voltages............................ 3:44
3:48 To Further Investigate the Effects of Electromagnetic
Induction ............................................................................. 3:57 3.4 Deleterious Effects of AC Interference.................................. 3:60 3.4.1
3.4.2 3.4.3 Electric Shock Hazards.......................................................
AC Corrosion ......................................................................
.1 Theory...........................................................................
.2 AC Corrosion Case Histories........................................
.3 AC Corrosion Field Test Proc...
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