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Table of Contents
                            CP Technol_Ch1_Final_April09
Chapter 1 Handouts
Chapter 2 Handouts
Chapter 3 Handouts
APPENDIX C U.S. Customary/Metric Conversion for Units of Measure
NACE SP0177-2007
NACE Standard TM0497-2002
	SP0169-2013(formerly RP0169)
	Section 1: General
	Section 2: Definitions, Abbreviations, and Acronyms
		Abbreviations and Acronyms:
	Section 3: Determination of Need for External Corrosion Control
		3.1 Introduction
		3.2 The need for external corrosion control should be based on data obtained from one or more of the following
	Section 4: Piping System Design
		4.1 Introduction
		4.2 External Corrosion Control
		4.3 Electrical Isolation
		4.4 Electrical Continuity
		4.5 Corrosion Control Test Stations
	Section 5: External Coatings
		5.1 Introduction
		5.2 Transport, Storage, Handling, Inspection, and Installation of Coated Pipe
	Section 6: Criteria and Other Considerations for Cathodic Protection
		6.1 Introduction
		6.2 Criteria
		6.3 Relevant Considerations
	Section 7: Design of Cathodic Protection Systems
		7.1 Introduction
		7.2 Major objectives of CP system design include the following:
		7.3 Information Useful for Design
		7.4 Types of CP Systems
		7.5 Considerations influencing selection of the type of CP system include the following:
		7.6 Factors Influencing Design of CP Systems
		7.7 Design Drawings and Specifications
	Section 8: Installation of CP Systems
		8.1 Introduction
		8.2 Construction Specifications
		8.3 Construction Supervision
		8.4 Galvanic Anodes
		8.5 Impressed Current Systems
		8.6 Corrosion Control Test Stations, Connections, and Bonds
		8.7 Electrical Isolation
	Section 9: Control of Stray Currents
		9.1 Introduction
		9.2 Mechanism of Interference-Current Corrosion (Stray-Current Corrosion)
		9.3 Detection of Stray Currents
		9.4 Methods for Mitigating Interference Corrosion Problems
		9.5 Indications of Resolved Interference Problems
	Section 10: Operation and Maintenance of CP Systems
		10.1 Introduction
		10.2 Representative potential measurements shall be obtained after each CP system is initially energized to determine whether the applicable criteria have been satisfied.
		10.3 The effectiveness of the CP system should be monitored annually. Longer or shorter intervals for monitoring might be appropriate, depending on the variability of CP factors, safety considerations, and economics of monitoring.
		10.4 Inspection and tests of CP facilities should be performed and documented to verify their proper operation and maintenance as follows:
		10.5 When pipe has been uncovered, it should be examined for evidence of external corrosion and, if externally coated, for condition of the external coating, including, but not limited to, any disbonded coating, noting whether corrosion is under the disbonded coating and pH of environment under the disbonded coating.
		10.6 The test equipment used for obtaining each electrical value should be of an appropriate type. Instruments and related equipment should be maintained in good operating condition and checked for accuracy.
		10.7 Remedial measures should be taken when periodic tests and inspections indicate that CP is no longer adequate. These measures may include the following:
		10.8 An electrical short circuit between a casing and carrier pipe can result in inadequate CP of the pipeline outside the casing because of reduction of protective current to the pipeline.12
		10.9 When the effects of electrical shielding of CP current are detected, the situation should be evaluated and appropriate action taken.
	Section 11: External Corrosion Control Records
		11.1 Introduction
		11.2 Relative to the determination of the need for external corrosion control, the following should be recorded (see Paragraph 7.3.3):
		11.3 Relative to structure design, the following should be recorded:
		11.4 Relative to the design of external corrosion control facilities, the following should be recorded:
		11.5 Relative to the installation of external corrosion control facilities, the following should be recorded:
		11.6 Records of surveys, inspections, and tests should be maintained to demonstrate that applicable criteria for interference control and CP have been satisfied.
		11.7 Relative to the maintenance of external corrosion control facilities, the following information should be recorded:
		11.8 Records sufficient to demonstrate the effectiveness of external corrosion control measures should be maintained as long as the facility involved remains in service. Other related external corrosion control records should be retained for such a period that satisfies individual company needs.
		11.9 Records sufficient to demonstrate adequate criteria used under Paragraph 6.2 must be maintained as long as the criteria are used to determine adequate CP.
	Appendix A  External Coatings Tables
	Appendix B  Review of International Standards
		Table 1a  Generic External Coating Systems for Carbon Steel Pipe with Material Requirements and Recommended Practices for Application for Underground and Submerged Pipe
		Table 1b  Generic External Coating Systems for Ductile Iron Pipe with Material Requirements and Recommended Practices for Application
		Table 2  Common Reference Electrodes and Their Potentials and Temperature Coefficients
		Table A1  References for General Use in the Installation and Inspection of External Coating Systems for Underground or Submerged Piping
		Table A2  External Coating System Characteristics Relative to Environmental Conditions(A)
		Table A3(a)  External Coating System Characteristics Related to Design and Construction
		Table A3(b)  External Coating System Characteristics Related to Design and ConstructionDesign and Construction Factor Recommended Test Methods
		Table A4  Methods for Evaluating Field Performance of External Coatings
		Figure 1: Residual Corrosion Rate of Carbon Steel Specimens as a Function of AC and CP Current Density. Laboratory Tests Performed in Simulated Soil Conditions.
		Figure 2: SCC Range of Pipe Steel in Carbonate/Bicarbonate Environments.72 Note: This figure is not applicable to all grades of steel and in all electrolytes. (For conversion, °F = 9/5 °C + 32).
Document Text Contents
Page 1

January 2014
Version 1.0

 NACE International, 2005

CP 3–Cathodic Protection



Page 2


The time and expertise of a many members of NACE International have gone
into the development of this course. Their dedication and efforts are greatly
appreciated by the authors of this course and by those who have assisted in
making this work possible.

The scope, desired learning outcomes and performance criteria were prepared
by the NACE Cathodic Protection Subcommittee under the auspices of the
NACE Certification and Education Committees. Special thanks go to this

Cathodic Protection Subcommittee

Paul Nichols Shell Global Solutions, Houston, Texas
Brian Holtsbaum CC Technologies, Calgary, Alberta
Don Mayfield Dominion Transmission, Delmont, Pennsylvania
Steve Nelson Columbia Gas Transmission, Charleston, West Virginia
Kevin Parker CC Technologies, Mt. Pleasant, Michigan
David A. Schramm ENEngineering, Woodridge,Illinois
Steve Zurbuchen OneOK Inc., Topeka, Kansas

This group of NACE members worked closely with the contracted course
developers, Rob Wakelin, CorrEng Consulting Service, Inc., (Downsview,
Ontario), Bob Gummow, CorrEng Consulting Service, Inc., (Downsview, Ontario)
and Tom Lewis, Loresco International (Hattiesburg, Mississippi).

Page 202

Interference 3:19

 NACE International, 2005 CP 3 Cathodic Protection Technologist
January 2014

3.2.2 Mitigation of Interference Effects from Impressed Current
Cathodic Protection Systems

A number of methods can be used to lessen the harmful effects of cathodic

protection system stray currents, as listed below:

 Remove the source or reduce its output.

 Install electrical isolating fittings in the interfered-with structure.

 Bury a metallic shield parallel to the interfered-with structure at the stray
current pick-up zone.

 Install additional cathodic protection at current discharge locations on the
interfered-with structure.

 Install a bond between the interfered-with and interfering structure.

 Apply a coating to the interfered-with structure in the area of stray current
pick-up or to the interfering structure where it picks up the returning stray


Before any mitigation activity can begin, conduct mutual interference tests where the

output of the suspected source is cyclically interrupted and field measurements are

taken in the presence of representatives of the interfering and interfered-with

companies involved. Interference cases are often reported through local electrolysis

committees, especially where there may be more than one interfered-with party.

Presuming a need for mitigation is determined, the mutually acceptable

mitigation technique(s) depend on the location and severity of the interference, on

the cathodic protection operational preferences of each party, and on the relative

capital and maintenance costs of the mitigation options.

3.2.2(a) Source Removal or Output Reduction

It is a difficult proposition to have a source removed if the interfering system was

present before the interfered-with structure was installed. However, in the opposite

situation, where the interfering source is newly installed, this method has greater


If the interference is caused primarily by the proximity of the interfered-with

structure to the interfering groundbed, it may not be necessary to remove the

transformer-rectifier but simply relocate the groundbed or reduce the current output.

Page 203

Interference 3:20

 NACE International, 2005 CP 3 Cathodic Protection Technologist
January 2014

Equation 3-5 or similar equations
can be used to estimate how remote a particular

groundbed needs to be from a foreign structure to minimize the interference effects.

It should be noted however that the voltage rise at any point distance x from the
groundbed is a percentage of the total voltage drop to remote earth (Vx,re/Vgb,re 

100). It is a function only of the geometry of the groundbed (i.e., its length, L) since

the groundbed current output and soil resistivity would not change. Therefore, only

the length parameter in the equation significantly affects the percentage.

Reducing the current output of the source is also a viable option as long as there are

safeguards to prevent the output from being raised inadvertently.

3.2.2(b) Installation of Isolating Fittings

Installation of isolating fittings as a stray current mitigation measure is an attempt to

increase the path resistance (Rs) of the interfered-with structure thus decreasing the

stray current (Is). This is seldom adequate as a standalone method.

The stray current will certainly be reduced but the lesser amount of stray current will

bypass each isolating fitting in the soil path thus creating several points of interference

as previously shown in Figure 3-19a. Consequently, additional cathodic protection

may be needed at each isolating joint to compensate for the residual stray current.

The installation of isolating fittings to electrically sectionalize piping systems as

illustrated in Figure 3-23 is a common practice.

2Von Baekmann, Schwenk, and Prinz, Cathodic Corrosion Protection, 3rd Edition Gulf Publishing, 1997,


Page 404

Evaluation of CP System Performance 5:63

 NACE International, 2005 CP 3–Cathodic Protection Technologist
January 2011

Problem 3:

Potentials (mV) Current (mA)

Ecorr structure = –550


Eoc, anode = –1,500 = 100

Estructure = –1,000

Eanode = –1,300


Estructure = –700 = 20

Eanode = –1,450

Eoc anode = –1,500

Problem 4:

The corrosion potential of a steel structure is –500 mV. When the cathodic

protection is applied using an impressed current system, the structure potential

shifts to –960 mV. Upon interrupting the current, the instant-off potential is

–610 mV. If all potentials are measured with respect to a copper/copper sulfate

reference electrode, which cathodic protection criteria are satisfied?

Problem 5:

A fixed-voltage rectifier is set to operate at an output of 30 V and 15 A. During

routine surveillance the rectifier is found to be 30 V and 7A. What malfunction(s)

could have occurred?

Group Case Study:

The figure below shows the plan and polarized potential profile for a portion of a

coated and cathodically protected pipeline. List at least seven possible causes for

the apparent lack of protection in the vicinity of the road crossing.

Page 405

Evaluation of CP System Performance 5:64

 NACE International, 2005 CP 3–Cathodic Protection Technologist
January 2011

Exercise Schematic 5-1:

Plan and Potential Profile for an Underground Cathodically

Protected Pipeline

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