Electrical Engineering Cathodic Protection

UFC 3-570-02N 16 January 2004

UNIFIED FACILITIES CRITERIA (UFC)

ELECTRICAL ENGINEERING CATHODIC

PROTECTION

APPROVED FOR PUBLIC RELEASE; DISTRIBUTION UNLIMITED

UFC 3-570-02N 16 January 2004

UNIFIED FACILITIES CRITERIA (UFC)

ELECTRICAL ENGINEERING CATHODIC PROTECTION

Any copyrighted material included in this UFC is identified at its point of use. Use of the copyrighted material apart from this UFC must have the permission of the copyright holder. U.S. ARMY CORPS OF ENGINEERS NAVAL FACILITIES ENGINEERING COMMAND (Preparing Activity) AIR FORCE CIVIL ENGINEERING SUPPORT AGENCY Record of Changes (changes indicated by \1\ ... /1/ ) Change No. Date Location

UFC 3-570-02N 16 January 2004

FOREWORD The Unified Facilities Criteria (UFC) system is prescribed by MIL-STD 3007 and provides planning, design, construction, sustainment, restoration, and modernization criteria, and applies to the Military Departments, the Defense Agencies, and the DoD Field Activities in accordance with USD(AT&L) Memorandum dated 29 May 2002. UFC will be used for all DoD projects and work for other customers where appropriate. All construction outside of the United States is also governed by Status of forces Agreements (SOFA), Host Nation Funded Construction Agreements (HNFA), and in some instances, Bilateral Infrastructure Agreements (BIA.) Therefore, the acquisition team must ensure compliance with the more stringent of the UFC, the SOFA, the HNFA, and the BIA, as applicable. UFC are living documents and will be periodically reviewed, updated, and made available to users as part of the Services responsibility for providing technical criteria for military construction. Headquarters, U.S. Army Corps of Engineers (HQUSACE), Naval Facilities Engineering Command (NAVFAC), and Air Force Civil Engineer Support Agency (AFCESA) are responsible for administration of the UFC system. Defense agencies should contact the preparing service for document interpretation and improvements. Technical content of UFC is the responsibility of the cognizant DoD working group. Recommended changes with supporting rationale should be sent to the respective service proponent office by the following electronic form: Criteria Change Request (CCR). The form is also accessible from the Internet sites listed below. UFC are effective upon issuance and are distributed only in electronic media from the following source: Whole Building Design Guide web site http://dod.wbdg.org/. Hard copies of UFC printed from electronic media should be checked against the current electronic version prior to use to ensure that they are current. AUTHORIZED BY: ______________________________________ DONALD L. BASHAM, P.E. Chief, Engineering and Construction U.S. Army Corps of Engineers

______________________________________DR. JAMES W WRIGHT, P.E. Chief Engineer Naval Facilities Engineering Command

______________________________________ KATHLEEN I. FERGUSON, P.E. The Deputy Civil Engineer DCS/Installations & Logistics Department of the Air Force

______________________________________Dr. GET W. MOY, P.E. Director, Installations Requirements and Management Office of the Deputy Under Secretary of Defense (Installations and Environment)

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CONTENTS

Page CHAPTER 1 INTRODUCTION Paragraph 1-1 PURPOSE AND SCOPE ....................................................... 1-1

1-2 APPLICABILITY..................................................................... 1-1 1-2.1 General Building Requirements ............................................. 1-1 1-2.2 Safety .................................................................................... 1-1 1-2.3 Fire Protection ....................................................................... 1-1 1-2.4 Antiterrorism/Force Protection ............................................... 1-1 1-3 REFERENCES ...................................................................... 1-1

APPENDIX A MIL-HDBK 1004/10..................... A-1

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CHAPTER 1

INTRODUCTION 1-1 PURPOSE AND SCOPE. This UFC is comprised of two sections. Chapter 1 introduces this UFC and provides a listing of references to other Tri-Service documents closely related to the subject. Appendix A contains the full text copy of the previously released Military Handbook (MIL-HDBK) on this subject. This UFC serves as criteria until such time as the full text UFC is developed from the MIL-HDBK and other sources.

This UFC provides general criteria for the design of cathodic protection.

Note that this document does not constitute a detailed technical design, maintenance or operations manual, and is issued as a general guide to the considerations associated with design of economical, efficient and environmentally acceptable heating plants. 1-2 APPLICABILITY. This UFC applies to all Navy service elements and Navy contractors; Army service elements should use the references cited in paragraph 1-3 below; all other DoD agencies may use either document unless explicitly directed otherwise. 1-2.1 GENERAL BUILDING REQUIREMENTS. All DoD facilities must comply with UFC 1-200-01, Design: General Building Requirements. If any conflict occurs between this UFC and UFC 1-200-01, the requirements of UFC 1-200-01 take precedence. 1-2.2 SAFETY. All DoD facilities must comply with DODINST 6055.1 and applicable Occupational Safety and Health Administration (OSHA) safety and health standards. NOTE: All NAVY projects, must comply with OPNAVINST 5100.23 (series), Navy Occupational Safety and Health Program Manual. The most recent publication in this series can be accessed at the NAVFAC Safety web site: www.navfac.navy.mil/safety/pub.htm. If any conflict occurs between this UFC and OPNAVINST 5100.23, the requirements of OPNAVINST 5100.23 take precedence. 1-2.3 FIRE PROTECTION. All DoD facilities must comply with UFC 3-600-01, Design: Fire Protection Engineering for Facilities. If any conflict occurs between this UFC and UFC 3-600-01, the requirements of UFC 3-600-01 take precedence. 1-2.4 ANTITERRORISM/FORCE PROTECTION. All DoD facilities must comply with UFC 4-010-01, Design: DoD Minimum Antiterrorism Standards for Buildings. If any conflict occurs between this UFC and UFC 4-010-01, the requirements of UFC 4-010-01 take precedence. 1-3 REFERENCES. The following Tri-Service publications have valuable information on the subject of this UFC. When the full text UFC is developed for this

UFC 3-570-02N 16 January 2004

1-1

subject, applicable portions of these documents will be incorporated into the text. The designer is encouraged to access and review these documents as well as the references cited in Appendix A. 1. US Army Corps of Engineers USACE TM 5-811-7, Electrical Design

Commander Cathodic Protection, 22 April 1985 USACE Publication Depot USACE TL 1110-3-474, Cathodic Protection ATTN: CEIM-IM-PD 14 July 1995 2803 52nd Avenue USACE TL 1110-9-10, Cathodic Protection Hyattsville, MD 20781-1102 System Using Ceramic Anodes, 05 January (301) 394-0081 fax: 0084 1991 [email protected]

http://www.usace.army.mil/inet/usace-docs/

UFC 3-570-02N 16 January 2004

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APPENDIX A

MIL-HDBK 1004/10 ELECTRICAL ENGINEERING CATHODIC PROTECTION

INCH-POUND

MIL-HDBK-1004/10

31 JANUARY 1990

MILITARY HANDBOOK


AMSC N/A

DISTRIBUTION STATEMENT A. APPROVED FOR PUBLIC RELEASE: DISTRIBUTION ISUNLIMITED

AREA FACR

MIL-HDBK-1004/10

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THIS PAGE INTENTIONALLY LEFT BLANK

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ABSTRACT

This manual is intended for use in the design and construction ofcathodic protection systems for the mitigation of corrosion of buried orsubmerged metallic structures. Design of cathodic protection systems issomewhat different than design of other electrical or mechanical systemsbecause it must be based upon local environmental conditions such as soilresistivity. This manual presents criteria for cathodic protection, meth-odologies for the determination of required environmental conditions, meth-odologies for design of cathodic protection systems, examples of typicalsystems and design calculations, installation and construction practices,recommended initial system checkout procedures, and system maintenancerequirements.

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MIL-HDBK-1004/10

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FOREWORD

This handbook has been developed from an evaluation of facilities in the shore establishment, from surveys of the availability of new materials andconstruction methods, and from selection of the best design practices of theNaval Facilities Engineering Command (NAVFACENGCOM), other Governmentagencies, and the private sector. This handbook was prepared using, to themaximum extent feasible, national professional society, association, andinstitute standards. Deviations from these criteria in the planning,engineering, design, and construction of Naval shore facilities cannot be madewithout prior approval of NAVFACENGCOM HQ (Code 04).

Design cannot remain static any more than can the functions it serves or thetechnologies it uses. Accordingly, recommendations for improvement areencouraged and should be furnished to Naval Civil Engineering Laboratory, CodeL30, Port Hueneme, CA 93043, telephone (805) 982-5743.

THIS HANDBOOK SHALL NOT BE USED AS A REFERENCE DOCUMENT FOR PROCUREMENT OFFACILITIES CONSTRUCTION. IT IS TO BE USED IN THE PURCHASE OF FACILITIESENGINEERING STUDIES AND DESIGN (FINAL PLANS, SPECIFICATIONS, AND COSTESTIMATES). DO NOT REFERENCE IT IN MILITARY OR FEDERAL SPECIFICATIONS OROTHER PROCUREMENT DOCUMENTS.

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ELECTRICAL ENGINEERING CRITERIA HANDBOOKS AND MANUALS

CriteriaManual Title PA

MIL-HDBK-1004/1 Electrical Engineering-Preliminary CHESDIVDesign Considerations

MIL-HDBK-1004/2 Power Distribution Systems PACDIV

MIL-HDBK-1004/3 Switchgear and Relaying CHESDIV

MIL-HDBK-1004/4 Electrical Utilization Systems CHESDIV

DM-4.05 400 Hz Medium Voltage Conversion/ SOUTHDIVDistribution and Low-Voltage Utilization Systems

MIL-HDBK-1004/6 Lightning Protection CHESDIV

DM-4.07 Wire Communication and Signal Systems CHESDIV

DM-4.09 Energy Monitoring and Control Systems HDQTRS

MIL-HDBK-1004/10 Electrical Engineering Cathodic NCELProtection

MIL-HDBK-1004/10

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CONTENTS

Page

Section 1 INTRODUCTION1.1 Scope. . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.2 Cancellation. . . . . . . . . . . . . . . . . . . . . . . . . 11.3 Related Technical Documents. . . . . . . . . . . . . . . . . 1

Section 2 CATHODIC PROTECTION CONCEPTS2.1 Corrosion as an Electrochemical Process. . . . . . . . . . . 32.1.1 Driving Force. . . . . . . . . . . . . . . . . . . . . . . . 32.1.2 The Electrochemical Cell. . . . . . . . . . . . . . . . . . . 32.1.2.1 Components of the Electrochemical Cell. . . . . . . . . . . . 32.1.2.2 Reactions in an Electrochemical Cell. . . . . . . . . . . . . 32.2 The Electrochemical Basis for Cathodic

Protection. . . . . . . . . . . . . . . . . . . . . . . . . . 42.2.1 Potentials Required for Cathodic Protection. . . . . . . . . 42.3 Practical Application of Cathodic Protection. . . . . . . . . 52.3.1 When Cathodic Protection Should Be Considered. . . . . . . . 52.3.1.1 Where Feasible. . . . . . . . . . . . . . . . . . . . . . . . 52.3.1.2 When Indicated By Experience. . . . . . . . . . . . . . . . . 52.3.1.3 As Required By Regulation. . . . . . . . . . . . . . . . . . 52.3.2 Functional Requirements for Cathodic Protection . . . . . . . 82.3.2.1 Continuity. . . . . . . . . . . . . . . . . . . . . . . . . . 82.3.2.2 Electrolyte. . . . . . . . . . . . . . . . . . . . . . . . . 82.3.2.3 Source of Current. . . . . . . . . . . . . . . . . . . . . . 82.3.2.4 Connection to Structure. . . . . . . . . . . . . . . . . . . 82.4 Sacrificial Anode Systems. . . . . . . . . . . . . . . . . . 82.4.1 Anode Materials. . . . . . . . . . . . . . . . . . . . . . . 92.4.2 Connection to Structure. . . . . . . . . . . . . . . . . . . 102.4.3 Other Requirements. . . . . . . . . . . . . . . . . . . . . . 102.5 Impressed Current Systems. . . . . . . . . . . . . . . . . . 102.5.1 Anode Materials. . . . . . . . . . . . . . . . . . . . . . . 102.5.2 Direct Current Power Source. . . . . . . . . . . . . . . . . 102.5.3 Connection to Structure. . . . . . . . . . . . . . . . . . . 102.5.4 Other Requirements. . . . . . . . . . . . . . . . . . . . . . 11

Section 3 CRITERIA FOR CATHODIC PROTECTION3.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . 133.2 Electrical Criteria. . . . . . . . . . . . . . . . . . . . . 133.3 Interpretation of Structure-to-Electrolyte

Potential Readings. . . . . . . . . . . . . . . . . . . . . . 133.3.1 National Association of Corrosion Engineers

(NACE)Standard RP-01-69. . . . . . . . . . . . . . . . . . . 133.3.1.1 Criteria for Steel. . . . . . . . . . . . . . . . . . . . . . 153.3.1.2 Criteria for Aluminum. . . . . . . . . . . . . . . . . . . . 153.3.1.3 Criteria for Copper. . . . . . . . . . . . . . . . . . . . . 153.3.1.4 Criteria for Dissimilar Metal Structures. . . . . . . . . . . 153.3.2 Other Electrical Criteria. . . . . . . . . . . . . . . . . . 153.3.2.1 Criteria for Lead. . . . . . . . . . . . . . . . . . . . . . 163.3.2.2 NACE RP-02-85. . . . . . . . . . . . . . . . . . . . . . . . 16

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3.4 Failure Rate Analysis. . . . . . . . . . . . . . . . . . . . 163.5 Nondestructive Testing of Facility. . . . . . . . . . . . . . 163.5.1 Visual Analysis. . . . . . . . . . . . . . . . . . . . . . . 163.6 Consequences of Underprotection. . . . . . . . . . . . . . . 173.7 Consequences of Overprotection. . . . . . . . . . . . . . . . 183.7.1 Coating Disbondment. . . . . . . . . . . . . . . . . . . . . 183.7.2 Hydrogen Embrittlement. . . . . . . . . . . . . . . . . . . . 18

Section 4 CATHODIC PROTECTION SYSTEM DESIGN PRINCIPLES4.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . 194.2 General Design Procedures. . . . . . . . . . . . . . . . . . 194.2.1 Drawings and Specifications. . . . . . . . . . . . . . . . . 194.2.1.1 Drawings and Specifications for the Structure to

be Protected. . . . . . . . . . . . . . . . . . . . . . . . . 194.2.1.2 Site Drawings. . . . . . . . . . . . . . . . . . . . . . . . 194.2.2 Field Surveys. . . . . . . . . . . . . . . . . . . . . . . . 204.2.2.1 Water Analysis. . . . . . . . . . . . . . . . . . . . . . . . 204.2.2.2 Soil Characteristics. . . . . . . . . . . . . . . . . . . . . 204.2.2.3 Current Requirement Tests. . . . . . . . . . . . . . . . . . 214.2.2.4 Location of Other Structures in the Area. . . . . . . . . . . 224.2.2.5 Availability of ac Power. . . . . . . . . . . . . . . . . . . 224.2.3 Current Requirements. . . . . . . . . . . . . . . . . . . . . 224.2.4 Choice of Sacrificial or Impressed Current

System. . . . . . . . . . . . . . . . . . . . . . . . . . . . 224.2.5 Basic Design Procedure for Sacrificial Anode

Systems. . . . . . . . . . . . . . . . . . . . . . . . . . 234.2.6 Basic Design Procedure for Impressed Current

Systems. . . . . . . . . . . . . . . . . . . . . . . . . . 244.2.6.1 Total Current Determination. . . . . . . . . . . . . . . . . 244.2.6.2 Total Resistance Determination. . . . . . . . . . . . . . . . 264.2.6.3 Voltage and Rectifier Determination. . . . . . . . . . . . . 274.2.7 Analysis of Design Factors. . . . . . . . . . . . . . . . . . 284.3 Determination of Field Data. . . . . . . . . . . . . . . . . 284.3.1 Determination of Electrolyte Resistivity . . . . . . . . . . 294.3.1.1 In Soils. . . . . . . . . . . . . . . . . . . . . . . . . . . 294.3.1.2 Liquids. . . . . . . . . . . . . . . . . . . . . . . . . . . 294.3.2 Chemical Analysis of the Environment . . . . . . . . . . . . 314.3.2.1 pH. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 314.3.3 Coating Conductance. . . . . . . . . . . . . . . . . . . . . 314.3.3.1 Short Line Method. . . . . . . . . . . . . . . . . . . . . . 334.3.3.2 Long Line Method. . . . . . . . . . . . . . . . . . . . . . . 334.3.4 Continuity Testing. . . . . . . . . . . . . . . . . . . . . . 354.3.4.1 Method 1. . . . . . . . . . . . . . . . . . . . . . . . . . . 354.3.4.2 Method 2. . . . . . . . . . . . . . . . . . . . . . . . . . . 354.3.4.3 Method 3. . . . . . . . . . . . . . . . . . . . . . . . . . . 354.3.5 Insulation Testing. . . . . . . . . . . . . . . . . . . . . . 354.3.5.1 Buried Structures. . . . . . . . . . . . . . . . . . . . . . 354.3.5.2 Aboveground Structures. . . . . . . . . . . . . . . . . . . . 384.4 Corrosion Survey Checklist. . . . . . . . . . . . . . . . . . 38

Section 5 PRECAUTIONS FOR CATHODIC PROTECTION SYSTEM DESIGN5.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . 395.2 Excessive Currents and Voltages. . . . . . . . . . . . . . . 39

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5.2.1 Interference. . . . . . . . . . . . . . . . . . . . . . . . . 395.2.1.1 Detecting Interference. . . . . . . . . . . . . . . . . . . . 415.2.1.2 Control of Interference - Anode Bed Location. . . . . . . . . 435.2.1.3 Control of Interference - Direct Bonding. . . . . . . . . . . 435.2.1.4 Control of Interference - Resistive Bonding. . . . . . . . . 455.2.1.5 Control of Interference - Sacrificial Anodes. . . . . . . . . 475.2.2 Effects of High Current Density. . . . . . . . . . . . . . . 475.2.3 Effects of Electrolyte pH. . . . . . . . . . . . . . . . . . 475.3 Hazards Associated with Cathodic Protection. . . . . . . . . 495.3.1 Explosive Hazards. . . . . . . . . . . . . . . . . . . . . . 495.3.2 Bonding for Electrical Safety. . . . . . . . . . . . . . . . 495.3.3 Induced Alternating Currents. . . . . . . . . . . . . . . . . 50

Section 6 IMPRESSED CURRENT SYSTEM 6.1 Advantages of Impressed Current Cathodic

Protection Systems. . . . . . . . . . . . . . . . . . . . . . 536.2 Determination of Circuit Resistance. . . . . . . . . . . . . 536.2.1 Anode-to-Electrolyte Resistance. . . . . . . . . . . . . . . 536.2.1.1 Effect on System Design and Performance. . . . . . . . . . . 536.2.1.2 Calculation of Anode-to-Electrolyte Resistance . . . . . . . 546.2.1.3 Basic Equations . . . . . . . . . . . . . . . . . . . . . . . 546.2.1.4 Simplified Expressions for Common Situations. . . . . . . . . 556.2.1.5 Field Measurement. . . . . . . . . . . . . . . . . . . . . . 576.2.1.6 Effect of Backfill. . . . . . . . . . . . . . . . . . . . . . 586.2.2 Structure-to-Electrolyte Resistance. . . . . . . . . . . . . 596.2.3 Connecting Cable Resistance. . . . . . . . . . . . . . . . . 596.2.4 Resistance of Connections and Splices. . . . . . . . . . . . 596.3 Determination of Power Supply Requirements. . . . . . . . . . 596.4 Selection of Power Supply Type. . . . . . . . . . . . . . . . 606.4.1 Rectifiers. . . . . . . . . . . . . . . . . . . . . . . . . . 606.4.2 Thermoelectric Generators. . . . . . . . . . . . . . . . . . 606.4.3 Solar. . . . . . . . . . . . . . . . . . . . . . . . . . . . 606.4.4 Batteries. . . . . . . . . . . . . . . . . . . . . . . . . . 606.4.5 Generators. . . . . . . . . . . . . . . . . . . . . . . . . . 606.5 Rectifier Selection. . . . . . . . . . . . . . . . . . . . . 606.5.1 Rectifier Components. . . . . . . . . . . . . . . . . . . . . 616.5.1.1 Transformer Component. . . . . . . . . . . . . . . . . . . . 616.5.1.2 Rectifying Elements. . . . . . . . . . . . . . . . . . . . . 616.5.1.3 Overload Protection. . . . . . . . . . . . . . . . . . . . . 616.5.1.4 Meters. . . . . . . . . . . . . . . . . . . . . . . . . . . . 636.5.2 Standard Rectifier Types . . . . . . . . . . . . . . . . . . 636.5.2.1 Single-Phase Bridge. . . . . . . . . . . . . . . . . . . . . 636.5.2.2 Single-Phase Center Tap. . . . . . . . . . . . . . . . . . . 636.5.2.3 Three-Phase Bridge. . . . . . . . . . . . . . . . . . . . . . 636.5.2.4 Three-Phase Wye. . . . . . . . . . . . . . . . . . . . . . . 656.5.2.5 Special Rectifier Types . . . . . . . . . . . . . . . . . . . 656.5.3 Rectifier Selection and Specifications. . . . . . . . . . . . 686.5.3.1 Available Features. . . . . . . . . . . . . . . . . . . . . . 696.5.3.2 Air Cooled Versus Oil Immersed. . . . . . . . . . . . . . . . 696.5.3.3 Selecting ac Voltage. . . . . . . . . . . . . . . . . . . . . 706.5.3.4 dc Voltage and Current Output. . . . . . . . . . . . . . . . 706.5.3.5 Filters. . . . . . . . . . . . . . . . . . . . . . . . . . . 70

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6.5.3.6 Explosion Proof Rectifiers. . . . . . . . . . . . . . . . . . 706.5.3.7 Lightning Arresters. . . . . . . . . . . . . . . . . . . . . 716.5.3.8 Selenium Versus Silicon Stacks. . . . . . . . . . . . . . . . 716.5.3.9 Other Options. . . . . . . . . . . . . . . . . . . . . . . . 716.5.3.10 Rectifier Alternating Current Rating. . . . . . . . . . . . . 716.6 Anodes for Impressed Current Systems. . . . . . . . . . . . . 736.6.1 Graphite Anodes. . . . . . . . . . . . . . . . . . . . . . . 746.6.1.1 Specifications. . . . . . . . . . . . . . . . . . . . . . . . 746.6.1.2 Available Sizes. . . . . . . . . . . . . . . . . . . . . . . 746.6.1.3 Characteristics. . . . . . . . . . . . . . . . . . . . . . . 776.6.1.4 Operation. . . . . . . . . . . . . . . . . . . . . . . . . . 776.6.2 High Silicon Cast Iron. . . . . . . . . . . . . . . . . . . . 786.6.3 High Silicon Chromium Bearing Cast Iron

(HSCBCI). . . . . . . . . . . . . . . . . . . . . . . . . . . 786.6.3.1 Specifications. . . . . . . . . . . . . . . . . . . . . . . . 786.6.3.2 Available Sizes. . . . . . . . . . . . . . . . . . . . . . . 796.6.3.3 Operation. . . . . . . . . . . . . . . . . . . . . . . . . . 796.6.4 Aluminum. . . . . . . . . . . . . . . . . . . . . . . . . . . 796.6.5 Platinum. . . . . . . . . . . . . . . . . . . . . . . . . . . 796.6.6 Platinized Anodes. . . . . . . . . . . . . . . . . . . . . . 796.6.6.1 Types. . . . . . . . . . . . . . . . . . . . . . . . . . . . 906.6.6.2 Operation. . . . . . . . . . . . . . . . . . . . . . . . . . 916.6.7 Alloyed Lead. . . . . . . . . . . . . . . . . . . . . . . . . 916.7 Other System Components. . . . . . . . . . . . . . . . . . . 916.7.1 Connecting Cables. . . . . . . . . . . . . . . . . . . . . . 916.7.1.1 Factors to be Considered. . . . . . . . . . . . . . . . . . . 916.7.1.2 Insulation. . . . . . . . . . . . . . . . . . . . . . . . . . 926.7.1.3 Recommended Cables for Specific Applications. . . . . . . . . 936.7.1.4 Economic Wire Size. . . . . . . . . . . . . . . . . . . . . . 936.7.2 Wire Splices and Connections. . . . . . . . . . . . . . . . . 946.7.3 Test Stations. . . . . . . . . . . . . . . . . . . . . . . . 966.7.4 Bonds. . . . . . . . . . . . . . . . . . . . . . . . . . . . 966.7.5 Insulating Joints. . . . . . . . . . . . . . . . . . . . . . 96

Section 7 SACRIFICIAL ANODE SYSTEM DESIGN7.1 Theory of Operation. . . . . . . . . . . . . . . . . . . . . 1137.1.1 Advantages of Sacrificial Anode Cathodic Protection Systems. . . . . . . . . . . . . . . . . . . . . . 1137.1.2 Disadvantages of Sacrificial Anode Cathodic Protection Systems. . . . . . . . . . . . . . . . . . . . . . 1137.2 Sacrificial Anode Cathodic Protection System

DesignProcedures. . . . . . . . . . . . . . . . . . . . . . . 1137.3 Determination of Current Required for Protection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1147.4 Determination of Anode Output. . . . . . . . . . . . . . . . 1147.4.1 Simplified Method for Common Situations. . . . . . . . . . . 1147.4.2 Determination of Output Using

Anode-to-Electrolyte Resistance. . . . . . . . . . . . . . . 1147.4.2.1 Calculation of Anode-to-Electrolyte Resistance. . . . . . . . 1147.4.2.2 Determination of Structure-to-Electrolyte

Resistance. . . . . . . . . . . . . . . . . . . . . . . . . 1157.4.2.3 Connecting Cable Resistance. . . . . . . . . . . . . . . . . 1157.4.2.4 Resistance of Connections and Splices. . . . . . . . . . . . 1157.4.2.5 Total Circuit Resistance. . . . . . . . . . . . . . . . . . . 115

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Page7.4.2.6 Anode-to-Structure Potential. . . . . . . . . . . . . . . . . 1157.4.2.7 Anode Output Current. . . . . . . . . . . . . . . . . . . . . 1157.4.3 Field Measurement of Anode Output. . . . . . . . . . . . . . 1167.5 Determination of Number of Anodes Required. . . . . . . . . . 1167.6 Determination of Anode Life. . . . . . . . . . . . . . . . . 1167.7 Seasonal Variation in Anode Output. . . . . . . . . . . . . . 1177.8 Sacrificial Anode Materials . . . . . . . . . . . . . . . . . 1177.8.1 Magnesium. . . . . . . . . . . . . . . . . . . . . . . . . . 1177.8.1.1 Composition. . . . . . . . . . . . . . . . . . . . . . . . . 1187.8.1.2 Anode Efficiency. . . . . . . . . . . . . . . . . . . . . . . 1187.8.1.3 Potentials. . . . . . . . . . . . . . . . . . . . . . . . . . 1197.8.1.4 Sizes. . . . . . . . . . . . . . . . . . . . . . . . . . . . 1197.8.1.5 Current Output. . . . . . . . . . . . . . . . . . . . . . . . 1197.8.1.6 Backfill. . . . . . . . . . . . . . . . . . . . . . . . . . . 1197.8.2 Zinc. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1197.8.2.1 Composition. . . . . . . . . . . . . . . . . . . . . . . . . 1257.8.2.2 Anode Efficiency. . . . . . . . . . . . . . . . . . . . . . . 1257.8.2.3 Potentials. . . . . . . . . . . . . . . . . . . . . . . . . . 1257.8.2.4 Sizes. . . . . . . . . . . . . . . . . . . . . . . . . . . . 1267.8.2.5 Current Output. . . . . . . . . . . . . . . . . . . . . . . . 1267.8.2.6 Backfill. . . . . . . . . . . . . . . . . . . . . . . . . . . 1267.8.3 Aluminum. . . . . . . . . . . . . . . . . . . . . . . . . . . 1267.8.3.1 Composition. . . . . . . . . . . . . . . . . . . . . . . . . 1277.8.3.2 Anode Efficiency. . . . . . . . . . . . . . . . . . . . . . . 1277.8.3.3 Potentials. . . . . . . . . . . . . . . . . . . . . . . . . . 1277.8.3.4 Sizes. . . . . . . . . . . . . . . . . . . . . . . . . . . . 1277.8.3.5 Current Output. . . . . . . . . . . . . . . . . . . . . . . . 1277.9 Other System Components . . . . . . . . . . . . . . . . . . . 1277.9.1 Connecting Wires. . . . . . . . . . . . . . . . . . . . . . . 1277.9.1.1 Determination of Connecting Wire Size and Type. . . . . . . . 1337.9.2 Connections and Splices. . . . . . . . . . . . . . . . . . . 1347.9.3 Bonds and Insulating Joints. . . . . . . . . . . . . . . . . 1347.9.4 Test Station Location and Function. . . . . . . . . . . . . . 1347.9.5 Backfill. . . . . . . . . . . . . . . . . . . . . . . . . . . 135

Section 8 TYPICAL CATHODIC PROTECTION 8.1 Diagrams of Cathodic Protection Systems. . . . . . . . . . . 137

Section 9 CATHODIC PROTECTION SYSTEM DESIGN EXAMPLES9.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . 1559.2 Elevated Steel Water Tank. . . . . . . . . . . . . . . . . . 1559.2.1 Design Data . . . . . . . . . . . . . . . . . . . . . . . . . 1569.2.2 Computations . . . . . . . . . . . . . . . . . . . . . . . . 1569.3 Elevated Water Tank (Where Ice is Expected). . . . . . . . . 1739.3.1 Design Data . . . . . . . . . . . . . . . . . . . . . . . . . 1769.3.2 Computations . . . . . . . . . . . . . . . . . . . . . . . . 1769.4 Steel Gas Main. . . . . . . . . . . . . . . . . . . . . . . . 1779.4.1 Design Data . . . . . . . . . . . . . . . . . . . . . . . . . 1809.4.2 Computations . . . . . . . . . . . . . . . . . . . . . . . . 1809.5 Gas Distribution System. . . . . . . . . . . . . . . . . . . 1849.5.1 Design Data . . . . . . . . . . . . . . . . . . . . . . . . . 1859.5.2 Computations . . . . . . . . . . . . . . . . . . . . . . . . 185

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9.6 Black Iron, Hot Water Storage Tank. . . . . . . . . . . . . . 1879.6.1 Design Data . . . . . . . . . . . . . . . . . . . . . . . . . 1889.6.2 Computations . . . . . . . . . . . . . . . . . . . . . . . . 1889.7 Underground Steel Storage Tank. . . . . . . . . . . . . . . . 1909.7.1 Design Data . . . . . . . . . . . . . . . . . . . . . . . . . 1909.7.2 Computations . . . . . . . . . . . . . . . . . . . . . . . . 1929.8 Heating Distribution System. . . . . . . . . . . . . . . . . 1929.8.1 Design Data . . . . . . . . . . . . . . . . . . . . . . . . . 1929.8.2 Computations . . . . . . . . . . . . . . . . . . . . . . . . 1939.8.3 Groundbed Design . . . . . . . . . . . . . . . . . . . . . . 1949.8.4 Rectifier Location. . . . . . . . . . . . . . . . . . . . . . 1959.9 Aircraft Multiple Hydrant Refueling System. . . . . . . . . . 1959.9.1 Design Data . . . . . . . . . . . . . . . . . . . . . . . . . 1959.9.2 Computations. . . . . . . . . . . . . . . . . . . . . . . . . 1969.10 Steel Sheet Piling in Seawater (Galvanic nodes). . . . . . . 1999.10.1 Design Data . . . . . . . . . . . . . . . . . . . . . . . . . 1999.10.2 Computations . . . . . . . . . . . . . . . . . . . . . . . . 2019.11 Steel Sheet Piling in Seawater (Impressed

Current 9.11.1 Design Data. . . . . . . . . . . . . . . . . . . . . . . . . 203

9.11.2 Computations . . . . . . . . . . . . . . . . . . . . . . . . 2039.12 Steel H Piling in Seawater (Galvanic Anodes). . . . . . . . . 2079.12.1 Design Data . . . . . . . . . . . . . . . . . . . . . . . . . 2089.12.2 Computations . . . . . . . . . . . . . . . . . . . . . . . . 2089.13 Steel H Piling in Seawater (Impressed Current). . . . . . . . 2109.13.1 Design Data . . . . . . . . . . . . . . . . . . . . . . . . . 2109.13.2 Computations . . . . . . . . . . . . . . . . . . . . . . . . 210

Section 10 INSTALLATION AND CONSTRUCTION PRACTICES10.1 Factors to Consider. . . . . . . . . . . . . . . . . . . . . 21310.2 Planning of Construction. . . . . . . . . . . . . . . . . . . 21310.3 Pipeline Coating. . . . . . . . . . . . . . . . . . . . . . . 21310.3.1 Over-the-Ditch Coating. . . . . . . . . . . . . . . . . . . . 21310.3.2 Yard Applied Coating. . . . . . . . . . . . . . . . . . . . . 21310.3.3 Joint and Damage Repair. . . . . . . . . . . . . . . . . . . 21410.3.4 Inspection. . . . . . . . . . . . . . . . . . . . . . . . . . 21410.4 Coatings for Other Structures. . . . . . . . . . . . . . . . 21410.5 Pipeline Installation. . . . . . . . . . . . . . . . . . . . 21410.5.1 Casings. . . . . . . . . . . . . . . . . . . . . . . . . . . 21410.5.2 Foreign Pipeline Crossings. . . . . . . . . . . . . . . . . . 21510.5.3 Insulating Joints. . . . . . . . . . . . . . . . . . . . . . 21510.5.4 Bonds. . . . . . . . . . . . . . . . . . . . . . . . . . . . 21610.6 Electrical Connections. . . . . . . . . . . . . . . . . . . . 21610.7 Test Stations. . . . . . . . . . . . . . . . . . . . . . . . 21610.8 Sacrificial Anode Installation. . . . . . . . . . . . . . . . 21610.8.1 Vertical. . . . . . . . . . . . . . . . . . . . . . . . . . . 21610.8.2 Horizontal. . . . . . . . . . . . . . . . . . . . . . . . . . 21710.9 Impressed Current Anode Installation. . . . . . . . . . . . . 21710.9.1 Vertical. . . . . . . . . . . . . . . . . . . . . . . . . . . 21910.9.2 Horizontal. . . . . . . . . . . . . . . . . . . . . . . . . . 21910.9.3 Deep Anode Beds. . . . . . . . . . . . . . . . . . . . . . . 21910.9.4 Other Anode Types. . . . . . . . . . . . . . . . . . . . . . 22510.9.5 Connections. . . . . . . . . . . . . . . . . . . . . . . . . 225

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10.10 Impressed Current Rectifier Installation. . . . . . . . . . . 225

Section 11 SYSTEM CHECKOUT AND INITIAL ADJUSTMENTS11.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . 22911.2 Initial Potential Survey. . . . . . . . . . . . . . . . . . . 22911.3 Detection and Correction of Interference. . . . . . . . . . . 22911.4 Adjustment of Impressed Current Systems. . . . . . . . . . . 22911.4.1 Uneven Structure-To-Electrolyte Potentials. . . . . . . . . . 22911.4.2 Rectifier Voltage and Current Capacity. . . . . . . . . . . . 23011.5 Adjustment of Sacrificial Anode Systems. . . . . . . . . . . 23011.5.1 Low Anode Current Levels. . . . . . . . . . . . . . . . . . . 23011.5.2 Inadequate Protection at Designed Current Levels . . . . . . 230

Section 12 MAINTAINING CATHODIC PROTECTION 12.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . 23112.2 Required Periodic Monitoring and Maintenance. . . . . . . . . 23112.3 Design Data Required for System Maintenance. . . . . . . . . 23112.3.1 Drawings. . . . . . . . . . . . . . . . . . . . . . . . . . . 23112.3.2 System Data. . . . . . . . . . . . . . . . . . . . . . . . . 23112.3.2.1 Design Potentials. . . . . . . . . . . . . . . . . . . . . . 23112.3.2.2 Current Output. . . . . . . . . . . . . . . . . . . . . . . . 23112.3.2.3 System Settings and Potential Readings. . . . . . . . . . . . 23112.3.2.4 Rectifier Instructions. . . . . . . . . . . . . . . . . . . . 23212.4 Basic Maintenance Requirements. . . . . . . . . . . . . . . . 23212.5 Guidance for Maintenance . . . . . . . . . . . . . . . . . . 23212.5.1 Agency Maintenance and Operations Manuals. . . . . . . . . . 23212.5.2 DOT Regulations. . . . . . . . . . . . . . . . . . . . . . . 23512.5.3 NACE Standards. . . . . . . . . . . . . . . . . . . . . . . . 235

Section 13 ECONOMIC ANALYSIS13.1 Importance of Economic Analysis. . . . . . . . . . . . . . . 23713.2 Economic Analysis Process. . . . . . . . . . . . . . . . . . 23713.2.1 Define the Objective. . . . . . . . . . . . . . . . . . . . . 23713.2.2 Generate Alternatives. . . . . . . . . . . . . . . . . . . . 23813.2.3 Formulate Assumptions. . . . . . . . . . . . . . . . . . . . 23813.2.4 Determine Costs and Benefits. . . . . . . . . . . . . . . . . 23813.2.4.1 Costs. . . . . . . . . . . . . . . . . . . . . . . . . . . . 23813.2.4.2 Benefits. . . . . . . . . . . . . . . . . . . . . . . . . . . 23913.2.5 Compare Costs and Benefits and RankAlternatives. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23913.2.6 Perform Sensitivity Analysis. . . . . . . . . . . . . . . . . 23913.3 Design of Cathodic Protection Systems. . . . . . . . . . . . 23913.4 Economic Analysis - Example 1 . . . . . . . . . . . . . . . . 24013.4.1 Objective. . . . . . . . . . . . . . . . . . . . . . . . . . 24013.4.2 Alternatives . . . . . . . . . . . . . . . . . . . . . . . . 24013.4.3 Assumptions . . . . . . . . . . . . . . . . . . . . . . . . . 24013.4.4 Cost/Benefit Analysis . . . . . . . . . . . . . . . . . . . . 24013.4.4.1 Cost - Alternative 1--Steel Line Without

Cathodic Protection. . . . . . . . . . . . . . . . . . . . . 24013.4.4.2 Cost - Alternative 2--Steel Line with Cathodic Protection. . . . . . . . . . . . . . . . . . . . . . . . . . 24213.4.4.3 Cost - Alternative 3--Plastic Line. . . . . . . . . . . . . . 24213.4.4.4 Benefits. . . . . . . . . . . . . . . . . . . . . . . . . . . 243

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13.4.5 Compare Costs/Benefits . . . . . . . . . . . . . . . . . . . 24313.5 Economic Analysis - Example 2 . . . . . . . . . . . . . . . . 24313.5.1 Objective. . . . . . . . . . . . . . . . . . . . . . . . . . 24313.5.2 Alternative . . . . . . . . . . . . . . . . . . . . . . . . . 24313.5.3 Assumptions . . . . . . . . . . . . . . . . . . . . . . . . . 24313.5.4 Cost/Benefit Analysis . . . . . . . . . . . . . . . . . . . . 24413.5.4.1 Cost - Alternative 1--Steel Line Without

Cathodic Protection. . . . . . . . . . . . . . . . . . . . . 24413.5.4.2 Cost - Alternative 2--Steel Line With Cathodic

Protection. . . . . . . . . . . . . . . . . . . . . . . . . . 24513.5.4.3 Benefits. . . . . . . . . . . . . . . . . . . . . . . . . . . 24613.5.5 Compare Costs/Benefits . . . . . . . . . . . . . . . . . . . 24613.5.6 Conclusions and Recommendations. . . . . . . . . . . . . . . 24713.6 Economic Analysis - Example 3 . . . . . . . . . . . . . . . . 24713.6.1 Objective. . . . . . . . . . . . . . . . . . . . . . . . . . 24713.6.2 Alternatives . . . . . . . . . . . . . . . . . . . . . . . . 24713.6.3 Assumptions . . . . . . . . . . . . . . . . . . . . . . . . . 24713.6.4 Cost/Benefit Analysis . . . . . . . . . . . . . . . . . . . . 24713.6.4.1 Cost - Alternative 1--Impressed Current Cathodic

Protection. . . . . . . . . . . . . . . . . . . . . . . . . 24713.6.4.2 Cost - Alternative 2--Galvanic Anode System. . . . . . . . . 24813.6.5 Compare Costs/Benefits . . . . . . . . . . . . . . . . . . . 24913.7 Economic Analysis - Example 4 . . . . . . . . . . . . . . . . 24913.7.1 Objective . . . . . . . . . . . . . . . . . . . . . . . . . . 24913.7.2 Alternatives . . . . . . . . . . . . . . . . . . . . . . . . 24913.7.3 Assumptions . . . . . . . . . . . . . . . . . . . . . . . . . 24913.7.4 Cost/Benefit Analysis . . . . . . . . . . . . . . . . . . . . 24913.7.4.1 Cost - Alternative 1--Cathodic Protection System

Maintenance Continued. . . . . . . . . . . . . . . . . . . 24913.7.4.2 Cost - Alternative 2--Cathodic Protection System

Maintenance Discontinued. . . . . . . . . . . . . . . . . . 25013.7.5 Compare Benefits and Costs . . . . . . . . . . . . . . . . . 25113.8 Economic Analysis Goal. . . . . . . . . . . . . . . . . . . . 251

Section 14 CORROSION COORDINATING COMMITTEE PARTICIPATION14.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . 25314.2 Functions of Corrosion Coordinating Committees. . . . . . . . 25314.3 Operation of the Committees. . . . . . . . . . . . . . . . . 25314.4 Locations of Committees. . . . . . . . . . . . . . . . . . . 253

APPENDIX

APPENDIX A UNDERGROUND CORROSION SURVEY CHECKLIST . . . . . . . . . . . 255B ECONOMIC LIFE GUIDELINES . . . . . . . . . . . . . . . . . . 265C PROJECT YEAR DISCOUNT FACTORS . . . . . . . . . . . . . . . . 267D PRESENT VALUE FORMULAE . . . . . . . . . . . . . . . . . . . 269E DOT REGULATIONS . . . . . . . . . . . . . . . . . . . . . . . 271

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FIGURES

Page

Figure 1 The Electrochemical Cell . . . . . . . . . . . . . . . . . . 6 2 Corrosion Cell - Zinc and Platinum in Hydrochloric Acid . . . . . . . . . . . . . . . . . . . 6 3 Cathodic Protection Cell . . . . . . . . . . . . . . . . . . 7 4 Hydraulic Analogy of Cathodic Protection . . . . . . . . . . 7 5 Sacrificial Anode Cathodic Protection/Impressed

Current Cathodic Protection . . . . . . . . . . . . . . . . 9 6 Structure-to Electrolyte Potential Measurement . . . . . . . 14 7 Failure Rate Versus Time . . . . . . . . . . . . . . . . . . 17 8 Temporary Cathodic Protection System for

Determining Current Requirements . . . . . . . . . . . . . 23 9 4-Pin Soil Resistivity Measurement . . . . . . . . . . . . . 3010 Soil Box for Determination of Resistivity . . . . . . . . . . 3011 pH Meter . . . . . . . . . . . . . . . . . . . . . . . . . . 3212 Antimony Electrode Potential Versus pH . . . . . . . . . . . 3213 Coating Conductance - Short Line Method . . . . . . . . . . . 3414 Coating Conductance - Long Line Method . . . . . . . . . . . 3415 Continuity Testing - Potential Method . . . . . . . . . . . . 3616 Continuity Testing - Potential Drop Method . . . . . . . . . 3617 Continuity Testing - Pipe Locator Method . . . . . . . . . . 3718 Insulation Testing - Two-Wire Test Station . . . . . . . . . 3719 Interference from Impressed Current

Cathodic Protection System . . . . . . . . . . . . . . . . 4020 Interference Due to Potential Gradients . . . . . . . . . . . 4121 Interference Testing . . . . . . . . . . . . . . . . . . . . 4222 Plot of Potentials from Interference Test . . . . . . . . . . 4223 Measurement of Current Flow in Structure . . . . . . . . . . 4424 Correction of Interferencce - Direct Bonding . . . . . . . . 4425 Correction of Interference - Resistive Bonding . . . . . . . 4526 Effects of Bonding on Interference Test Potentials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4627 Bonding for Continuity . . . . . . . . . . . . . . . . . . . 4828 Control of Interference - Sacrificial Anode . . . . . . . . . 4829 Interference Due to Cathodic Protection of Quaywall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5030 Correction of Interference - Bonding . . . . . . . . . . . . 5131 Equavalent Cathodic Protection Circuit . . . . . . . . . . . 5432 Single-Phase - Full-Wave Bridge Rectifier . . . . . . . . . . 6233 Full-Wave Rectified Current . . . . . . . . . . . . . . . . . 6434 Single-Phase - Center Tap Circuit . . . . . . . . . . . . . . 6435 Three-Phase Bridge Circuit . . . . . . . . . . . . . . . . . 6536 Three-Phase Wye Circuit . . . . . . . . . . . . . . . . . . . 6637 Half-Wave Rectified Current . . . . . . . . . . . . . . . . . 6638 Constant Current Rectifier . . . . . . . . . . . . . . . . . 6739 Constant Potential Rectifier . . . . . . . . . . . . . . . . 6740 Multicircuit Constant Current Rectifier . . . . . . . . . . . 6841 Efficiency Versus Voltage - Selenium Stacks . . . . . . . . . 7242 Efficiency Versus Voltage - Silicon Stacks . . . . . . . . . 7343 Anode-to-Cable Connection - Graphite Anode . . . . . . . . . 7544 Center Connected Graphite Anode . . . . . . . . . . . . . . . 7645 Duct Anode . . . . . . . . . . . . . . . . . . . . . . . . . 8346 Button Anode . . . . . . . . . . . . . . . . . . . . . . . . 83

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47 Bridge Deck Anode - Type I . . . . . . . . . . . . . . . . . 8448 Bridge Deck Anode - Type II . . . . . . . . . . . . . . . . . 8549 Tubular Anode . . . . . . . . . . . . . . . . . . . . . . . . 8650 Anode to Cable Connection - Epoxy Seal . . . . . . . . . . . 8751 Anode to Cable Connection - Teflon Seal . . . . . . . . . . . 8852 Center Connected High Silicon Chromium

Bearing Cast Iron Anode . . . . . . . . . . . . . . . . . . 8953 Typical Platinized Anode . . . . . . . . . . . . . . . . . . 9054 Flush-Mounted Potential Test Station . . . . . . . . . . . . 9755 Soil Contact Test Station . . . . . . . . . . . . . . . . . . 9856 IR Drop Test Station . . . . . . . . . . . . . . . . . . . . 9957 Insulating Flange Test Station (Six-Wire) . . . . . . . . . . 10058 Wiring for Casing Isolation Test Station . . . . . . . . . . 10159 Bond Test Station . . . . . . . . . . . . . . . . . . . . . . 10160 Anode Balancing Resistors . . . . . . . . . . . . . . . . . . 10261 Bonding of a Dresser-Style Coupling . . . . . . . . . . . . . 10362 Bonding Methods for Cast Iron Bell-and-Spigot Pipe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10463 Isolating a Protected Line from an Unprotected Line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10564 Electrical Bond . . . . . . . . . . . . . . . . . . . . . . . 10665 Thermosetting-Resin Pipe Connection . . . . . . . . . . . . . 10666 Clamp Type Bonding Joint . . . . . . . . . . . . . . . . . . 10767 Underground Splice . . . . . . . . . . . . . . . . . . . . . 10868 Welded Type Bonding Joint for Slip-On

Pipe Installed Aboveground . . . . . . . . . . . . . . . . 10969 Test Box for an Insulating Fitting . . . . . . . . . . . . . 11070 Steel Insulating Joint Details for Flanged

Pipe Installed Below Grade . . . . . . . . . . . . . . . . 11171 Steel Insulating Joint Details for Aboveground

Flanged Pipe . . . . . . . . . . . . . . . . . . . . . . . 11272 Insulating Joint Details for Screwed Pipe

Connections . . . . . . . . . . . . . . . . . . . . . . . . 11273 Efficiency Versus Current Density - Magnesium

Anodes . . . . . . . . . . . . . . . . . . . . . . . . . . 11874 Aluminum Alloy Bracelet Anodes . . . . . . . . . . . . . . . 13375 Current-Potential Test Station . . . . . . . . . . . . . . . 13576 Typical Building Underground Heat & Water Lines . . . . . . . 13877 Impressed Current Point Type Cathodic Protection

for Aircraft Hydrant Refueling System . . . . . . . . . . . . 13878 Galvanic Anode Type Cathodic Protection for

Coated Underground Sewage Lift Station . . . . . . . . . . . 13979 Zinc Anode on Reinforced Concrete Block . . . . . . . . . . . 14080 Radiant Heat or Snow-Melting Piping . . . . . . . . . . . . . 14181 Cathodic Protection of Foundation Piles . . . . . . . . . . . 14282 Impressed Current Cathodic Protection for

Existing On-Grade Storage Tank . . . . . . . . . . . . . . 14283 Impressed Current Cathodic Protection with

Horizontal Anodes for On-Grade Storage Tank - New Installation . . . . . . . . . . . . . . . . . . . . . . . 143

84 On-Grade Fresh Water Tank Using Suspended Anodes . . . . . . 14485 Open Water Box Cooler . . . . . . . . . . . . . . . . . . . . 14486 Horizontal Hot Water Tank - Magnesium Anode

Installation . . . . . . . . . . . . . . . . . . . . . . . 145

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87 Impressed Current Cathodic Protection System for Sheet Piling for Wharf Construction . . . . . . . . . . . . 146

88 Suspended Anode Cathodic Protection for H-Pilingin Seawater . . . . . . . . . . . . . . . . . . . . . . . . . 146

89 Cathodic Protection for H-Piling in Seawater . . . . . . . . 14790 Cellular Earth Fill Pier Supports . . . . . . . . . . . . . . 14891 Elevated Fresh Water Tank Using Suspended Anodes . . . . . . 14992 Cathodic Protection of Tanks using Rigid

Floor-Mounted Anodes . . . . . . . . . . . . . . . . . . . 15093 Cathodic Protection of Hydraulic Elevator

Cylinders . . . . . . . . . . . . . . . . . . . . . . . . . . 15194 Hydraulic Hoist Cylinder . . . . . . . . . . . . . . . . . . 15295 Typical Cathodic Protection of Underground Tank

Farm . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15396 Gasoline Service Station System . . . . . . . . . . . . . . . 15497 Segmented Elevated Tank for Area Calculations . . . . . . . . 15798 Anode Spacing for Elevated Steel Water Tank . . . . . . . . . 16099 Anode Suspension Arrangement for Elevated

Steel Water Tank . . . . . . . . . . . . . . . . . . . . . 162100 Equivalent Diameter for Anodes in a

Circle in Water Tank . . . . . . . . . . . . . . . . . . . 163101 Fringe Factor for Stub Anodes . . . . . . . . . . . . . . . . 164102 Elevated Steel Water Tank Showing Rectifier and

Anode Arrangement . . . . . . . . . . . . . . . . . . . . . 172103 Hand Hole and Anode Suspension Detail for Elevated Water Tank . . . . . . . . . . . . . . . . . . . . . . . . . 174104 Riser Anode Suspension Detail for Elevated Water Tank . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174105 Dimensions: Elevated Steel Water Tank . . . . . . . . . . . 175106 Cathodic Protection for Tanks Using Rigid Mounted . . . . . . 178

Button-Type Anodes and Platinized Titanium Wire107 Cathodic Protection System for Gas Main . . . . . . . . . . . 179108 Layout of Gas Piping in Residential District . . . . . . . . 184109 Cathodic Protection for Black Iron, Hot Water

Storage Tank . . . . . . . . . . . . . . . . . . . . . . . . 187110 Galvanic Anode Cathodic Protection of

Underground Steel Storage Tank . . . . . . . . . . . . . . . 191111 Impressed Current Cathodic Protection for Heating Conduit System . . . . . . . . . . . . . . . . . . . . . . . . 193112 Galvanic Anode Cathodic Protection for Hydrant Refueling System . . . . . . . . . . . . . . . . . . . . . . 197113 Galvanic Anode Cathodic Protection System for

Steel Sheet Piling Bulkhead . . . . . . . . . . . . . . . . . 200114 Impressed Current Cathodic Protection System

for Steel Sheet Piling Bulkhead . . . . . . . . . . . . . . . 207115 Pier Supported by H Piling for Para. 9.12 . . . . . . . . . . 208116 Test Station for Under-Road Casing Isolation . . . . . . . . 215117 Vertical Sacrificial Anode Installation . . . . . . . . . . . 217118 Horizontal Sacrificial Anode Installation When

Obstruction is Encountered . . . . . . . . . . . . . . . . 218119 Horizontal Sacrificial Anode Installation -

Limited Right-of-Way . . . . . . . . . . . . . . . . . . . 218120 Vertical HSCBCI Anode Installation . . . . . . . . . . . . . 220

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121 Vertical HSCBCI Anode Installation With Packaged Backfill . . . . . . . . . . . . . . . . . . . . . . . . . 221

122 Horizontal HSCBCI Anode Installation . . . . . . . . . . . . 222123 Typical Deep Well Anode Cathodic Protection

Installation . . . . . . . . . . . . . . . . . . . . . . . 223124 Deep Anode Installation Details . . . . . . . . . . . . . . . 224125 Typical Pole-Mounted Cathodic Protection

Rectifier Installation . . . . . . . . . . . . . . . . . . 226126 Typical Pad-Mounted Cathodic Protection

Rectifier Installation . . . . . . . . . . . . . . . . . . 227127 Form for Recording and Reporting Monthly

Rectifier Readings . . . . . . . . . . . . . . . . . . . . . 233128 Form for Recording and Reporting Quarterly

Structure-to-Electrode Potentials . . . . . . . . . . . . 234

TABLES

Table 1 Current Requirements for Cathodic Protection of Bare Steel . . . . . . . . . . . . . . . . . . . . . . . . . 202 Current Requirements for Cathodic Protection of

Coated Steel . . . . . . . . . . . . . . . . . . . . . . . 213 Galvanic Anode Size Factors . . . . . . . . . . . . . . . . . 254 Structure Potential Factor . . . . . . . . . . . . . . . . . 265 Adjusting Factor for Multiple Anodes (F) . . . . . . . . . . 276 Corrections Factors - Short Line Coating Conductance . . . . 337 Results of Structure-to-Electrolyte

Potential Measurements . . . . . . . . . . . . . . . . . . 438 Standard HSCBCI Anodes . . . . . . . . . . . . . . . . . . . 809 Special HSCBCI Anodes . . . . . . . . . . . . . . . . . . . . 8210 Standard Wire Characteristics . . . . . . . . . . . . . . . . 9211 M Factors for Determining Economic Wire Size

(Cost of losses in 100 feet of copper cable at 1 cent per kWhr) . . . . . . . . . . . . . . . . . . . . 95

12 Standard Alloy Magnesium Anodes - Standard Sizes for Use in Soil . . . . . . . . . . . . . . . . . . . 120

13 Standard Alloy Magnesium Anodes - Standard Sizes for Use in Water . . . . . . . . . . . . . . . . . . 121

14 Standard Alloy Magnesium Anodes -Standard Sizes for Condensors and Heat Exchangers . . . . . . . . . 121

15 Standard Alloy Magnesium Anodes - Elongated . . . . . . . . . 12216 High Potential Alloy Magnesium Anodes - Standard

Sizes for Soil and Water . . . . . . . . . . . . . . . . . 12217 Standard Alloy Magnesium Anodes - Standard Size

Extruded Rod for Water Tanks and Water Heaters . . . . . . 12318 Zinc Anodes - Standard Sizes for Underground or

Fresh Water . . . . . . . . . . . . . . . . . . . . . . . . 12319 Zinc Anodes - Special Sizes for Underground or

Fresh Water . . . . . . . . . . . . . . . . . . . . . . . . 12420 Zinc Anodes - Standard Sizes for Use in Seawater . . . . . . 12421 Zinc Anodes - Special Sizes for Use in Seawater . . . . . . . 12522 Aluminum Pier and Piling Anodes - Standard Sizes . . . . . . 128

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23 Type I Aluminum Alloy Anodes - Standard Sizes for Offshore Use . . . . . . . . . . . . . . . . . . . . . 129

24 Type III Aluminum Alloy Anodes for Offshore Use . . . . . . . 13025 Aluminum Alloy Hull Anodes - Standard Sizes

(Types I, II, and III) . . . . . . . . . . . . . . . . . . 13226 Aluminum Alloy Bracelet Anode - Standard Sizes . . . . . . . 13327 Technical Data - Commonly Used HSCBCI Anodes . . . . . . . . 161

REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 287

GLOSSARY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 289

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Section 1: INTRODUCTION

1.1 Scope. This handbook shall be used for the engineering design ofcathodic protection systems. Specifically described and discussed arecriteria for cathodic protection, system design principles, system examplesand their design steps, and economic analysis. To facilitate userapplication, sections on installation and construction practices, systemcheckout and initial adjustment, and system maintenance are included.

1.2 Cancellation. This handbook supersedes the cathodic protectioninformation of DM-4.06, Lightning and Cathodic Protection of December 1979.

1.3 Related Technical Documents. The following publications should beobtained to use with this document:

a) National Association of Corrosion Engineers (NACE) StandardRP-01-69 (1983 Rev), Recommended Practice for Control of External Corrosion onUnderground or Submerged Piping Systems.

b) NACE Standard RP-02-85, Control of External Corrosion onMetallic Buried, Partially Buried, or Submerged Liquid Storage Systems.

c) NACE Standard RP-50-72, Design, Installation and Maintenance ofImpressed Current Deep Groundbeds.

d) Naval Facilities Engineering Command (NAVFAC) P-442, EconomicAnalysis Handbook.

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Section 2: CATHODIC PROTECTION CONCEPTS

2.1 Corrosion as an Electrochemical Process. Corrosion of metals is aresult of electrochemical reactions. An electrochemical reaction is achemical reaction accompanied by a flow of electrical current.

2.1.1 Driving Force. The driving force for the corrosion of metalsthrough electrochemical reactions is the free energy of the metal atoms intheir metallic form. All chemical systems tend to change so that the freeenergy present is at a minimum. This is analogous to the flow of waterdownhill to minimize the free energy due to gravity. Most engineering metalsare found in nature in a form with low free energy. These metal ores arechemical compounds consisting of the metal atoms combined with other atomssuch as oxygen or sulfur. The process of breaking up these ores into theirmetallic and non-metallic atoms involves an addition of energy in order tofree the metal atoms from the natural, low energy content chemical compounds. The corrosion process is driven by the tendency of these metal atoms to revertto their natural state. If corrosion products are analyzed, their chemicalcomposition is usually identical to the ore from which the metal wasoriginally obtained.

2.1.2 The Electrochemical Cell. Electrochemical reactions occur througha combination of chemical reactions and the exchange of electrical charges(current) between areas where these chemical reactions are occurring. Theentire process is commonly known as an electrochemical cell. This process isdescribed in the following paragraphs.

2.1.2.1 Components of the Electrochemical Cell. Every electrochemical cellconsists of an anode, a cathode, an electrolyte and a metallic path for theflow of electrical current between the anode and cathode. A schematicelectrochemical cell is shown in Figure 1.

2.1.2.2 Reactions in an Electrochemical Cell. Chemical oxidation occurs atthe anode in an active electrochemical cell. Chemical oxidation is a reactionwhere an atom or molecule gives up electrons. The chemical shorthand for atypical oxidation reaction is:

EQUATION: M -> M + e (1)o + -

where

M = metal atomoM = metal ion+e = electron-

In this reaction the metal atom, which in combination with the other atoms ina piece of metal has high strength and other metallic properties, istransformed into a metal ion which usually dissolves. The electron isavailable for transfer to another site of lower electrical potential.

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At the cathode in an active electrochemical cell, chemicalreduction occurs. Chemical reduction is a reaction where an atom or moleculegains electrons. The chemical shorthand for a typical reduction reaction is:

EQUATION: R + e -> R (2)+ o-

where

R = positive ion in solution+e = electron-

R = reduced atom o

A reduced atom may either be discharged as a gas or may be deposited on thecathode. The electrolyte in an electrochemical cell serves as a source ofmaterial for the chemical reactions, a medium for the deposition of theproducts of the chemical reactions, and a path for the flow of charged ions insolution. The electron path, usually a metallic connection, is required sothat the electrons produced at the anode can flow from the anode to the sitesat the cathode where they are consumed. The electrochemical cell consists ofan anode where electrons are produced by a chemical reaction, a cathode whereelectrons are consumed by a chemical reaction different than the one occurringat the anode, an electrolyte for the flow of ions, and a metallic path for theflow of electrons (dc current).

Figure 2 shows an example of a corrosion cell where zinc isconnected to platinum in hydrochloric acid. The zinc corrodes at the anode,hydrogen gas forms at the cathode, and electric current flows through theexternal electron path. This electric current can be made to do useful work. An ordinary dry cell battery is an electrochemical cell. When in storage, theelectron path is not completed and the electrochemical reaction which producesthe current is only allowed to proceed when the external metallic path iscompleted.

2.2 The Electrochemical Basis for Cathodic Protection. Cathodicprotection utilizes a flow of direct current electricity to interfere with theactivity of the electrochemical cell responsible for corrosion. As shown inFigure 3, corrosion can be prevented by coupling a metal with a more activemetal when both are immersed in an electrolyte and connected with an externalpath. In this case the entire surface of the metal being protected becomes acathode; thus the term "cathodic protection."

2.2.1 Potentials Required for Cathodic Protection. Every metal immersedin an electrolyte develops an electrochemical potential due to the free energyof the atoms in the metal. In order to prevent anodic reactions fromoccurring due to electrochemical reactions on that metal, electrons must beprevented from leaving the metal. Since electrons can only flow from an areaof high (negative) potential to an area with lower (negative) potential,connection of the metal to be protected to a source of more negative electronscan effectively prevent the anodic reaction on the metal to be protected andcan thus prevent corrosion. In this case, the flow of electrons is from theexternal source to the metal being protected. Conventional current flow isdescribed by the flow of imaginary positive charges in a direction oppositethe electron flow.

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Since cathodic protection depends on the energy of electrons andtheir tendency to flow only from an area of high (negative) potential to oneof lower (negative) potential, the principle of cathodic protection can alsobe demonstrated through a hydraulic analogy (see Figure 4). In this analogythe surge tank is the metal to be protected. Flow from the surge tank isprevented by coupling the tank to a supply of water at higher pressure,leaving the tank full.

2.3 Practical Application of Cathodic Protection. Cathodic protectionis only one of many methods of corrosion control. Cathodic protection shouldbe evaluated as one alternative method to control corrosion in an overallcorrosion control program. Application of cathodic protection should beevaluated on the basis of technical feasibility, economic analysis, and systemfunctional requirements such as reliability and consequence of failure. Insome cases (e.g., underground pipelines), field experience has shown thatcathodic protection is such an effective means of providing the requiredlevels of safety in the operation of the systems that cathodic protection isrequired by Federal regulation.

2.3.1 When Cathodic Protection Should Be Considered. Cathodic protectionshould be considered, possibly in conjunction with other forms of corrosioncontrol such as the application of protective coatings, wherever the system isexposed to an aggressive environment in such a manner that cathodic protectionis technically and economically feasible.

2.3.1.1 Where Feasible. Cathodic protection is primarily feasible when thesurfaces to be protected are buried or submerged. External surfaces of buriedmetallic structures, surfaces of metal waterfront structures such as sheetpilings or bearing piles, and the internal surfaces of tanks containingelectrolytes such as water are applications where cathodic protection isusually technically feasible and is commonly utilized in protecting suchstructures. Cathodic protection has limited applicability on internalsurfaces of small diameter pipelines and other areas where ion flow in theelectrolyte is restricted by electrolyte resistance.

2.3.1.2 When Indicated By Experience. When construction of a new buried orsubmerged system is being planned, the corrosivity of the environment shouldbe considered as one of the factors in the design of the system. Ifexperience with similar systems in the vicinity of the construction site hasshown that the site conditions are aggressive based upon leak and failurerecords, cathodic protection should be provided as a means of controllingcorrosion on the new system. Cathodic protection is one of the few methods ofcorrosion control that can be effectively used to control corrosion ofexisting buried or submerged metal surfaces. Thus, if leak records on anexisting system show that corrosion is occurring, cathodic protection may beapplied to stop the corrosion damage from increasing. Cathodic protectioncan, however, only stop further corrosion from occurring and cannot restorethe material already lost due to corrosion.

2.3.1.3 As Required By Regulation. Regulations by the Department ofTransportation (DOT) have established standards for the transportation ofcertain liquids and compressed gas by pipelines in order to establish minimumlevels of safety. These regulations require that these pipelines be protectedby cathodic protection combined with other means of corrosion control such as

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protective coatings and electrical insulation. These regulations provideexcellent guidelines for the application of cathodic protection to buried andsubmerged pipelines. The pertinent sections of these regulations are includedherein as Appendix E.

Due to the safety and environmental consequences of system failure,there are also increasing numbers of federal, state, and local governmentalregulations regarding the storage and transportation of certain materials thatrequire corrosion control. Many of these regulations either make theapplication of cathodic protection mandatory on existing facilities as aprimary means of corrosion control or allow it to be selected as a means forthe mandatory control of corrosion on new facilities.

2.3.2 Functional Requirements for Cathodic Protection. In order to betechnically feasible, cathodic protection requires that the protectedstructure be electrically continuous and immersed in an electrolyte ofsufficient volume to allow the distribution of current onto the structure.

2.3.2.1 Continuity. Electrical continuity of the structure to be protectedmay be through metallic continuity provided by bolting, or welding of thestructure. Continuity is often achieved or insured by means of electricalconnections installed specifically to insure the effectiveness of cathodicprotection. These connections are commonly called "bonds."

2.3.2.2 Electrolyte. The electrolyte is commonly water or the watercontained in moist earth. The conductivity of the electrolyte is an importantfactor in the determination of the need for cathodic protection and in thedesign of cathodic protection systems.

2.3.2.3 Source of Current. Cathodic protection also requires the presenceof a source of electrical current at the proper voltage or potential toprevent attack on the structure. These sources of current are commonly called"anodes." As described below, the anodes may be fabricated from an activemetal such as magnesium, or zinc which provides a high potential source ofelectrons through corrosion on its surface. The anodes may also be fabricatedfrom a relatively inert material which has the ability to pass current fromits surface without being consumed at a high rate but which requires the useof an external energy source to increase the potential of the electronssupplied to the structure being protected. Anodes made from active metal arecommonly called "sacrificial" or "galvanic" anodes, as the anode material issacrificed to protect the structure under protection. The inert anodes arecommonly called "impressed current" anodes as the external energy source isused to impress a current onto the structure under protection.

2.3.2.4 Connection to Structure. The anodes must be electrically connectedto the structure through a metallic connection in order to complete thecircuit of the electrochemical cell responsible for the protection of thestructure.

2.4 Sacrificial Anode Systems. Cathodic protection in the sacrificialanode system is essentially a controlled electrochemical cell (see Figure 5). Corrosion on the protected structure is shifted to the anode. The anode isconsumed in the process but is designed and installed so that it is easilyreplaced when consumed. Anode life of 10 to 15 years is common. Anode lifeis dependent upon the amount of current emitted by the anodes and their size.If the cathodic protection system is properly designed and installed, and ifit is properly maintained (including periodic replacement of anodes asnecessary), the structure being protected is essentially immune to corrosiveattack and its lifetime is limited by other factors such as missionrequirements or mechanical damage.

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2.4.1 Anode Materials. The materials used for sacrificial anodes areither relatively pure active metals such as zinc or magnesium, or alloysmagnesium or aluminum that have been specifically developed for use assacrificial anodes. In applications where the anodes are buried, a specichemical backfill material surrounds the anode in order to insure that thanode will produce the desired output.

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2.4.2 Connection to Structure. Sacrificial anodes are normally suppliedwith either lead wires or cast-in straps to facilitate their connection to thestructure being protected. The lead wires may be attached to the structure bywelding or mechanical connections. These should have a low resistance andshould be insulated to prevent increased resistance or damage due tocorrosion. Where anodes with cast-in straps are used, the straps should bewelded directly to the structure if possible, or, if welding is not possible,used as locations for attachments using mechanical fasteners. A lowresistance mechanically adequate attachment is required for good protectionand resistance to mechanical damage. Welded connections are preferred toavoid the increase in resistance that can occur with mechanical connections.

2.4.3 Other Requirements. As for all systems to be protected, thestructure being protected by sacrificial anodes must be electricallycontinuous. The system should also include test stations that are used tomonitor the performance and to adjust the system for proper operation. As inall mechanical and electrical systems, cathodic protection systems requireperiodic inspection, maintenance, and adjustment for satisfactory operation.

2.5 Impressed Current Systems. From the standpoint of the structurebeing protected, cathodic protection using the impressed current method isessentially the same as in the sacrificial anode system. As shown in Figure5, the cathodic protection system supplies high energy electrons to thestructure being protected and the circuit of the electrochemical cell iscompleted through the soil. However, in the impressed current system, a

supply of direct electrical current is used to develop the potentialdifference between the anode and the structure being protected. Consumptionof the anode is not the driving force for the flow-protective current. Aproperly designed, installed, and maintained impressed current cathodicprotection system is as effective as the galvanic anode type of system inpreventing corrosion of the structure being protected.

2.5.1 Anode Materials. The materials commonly used for impressed currentcathodic protection have the capability of passing a current into theenvironment without being consumed at a high rate. Graphite and high siliconcast iron are the most commonly used impressed current cathodic protectionanode materials; however, other materials such as magnetite, platinum, andnewly developed oxide coated ceramic materials have been successfully used. For buried anodes, a backfill consisting of carbonaceous material is normallyused: to decrease the electrical resistance of the anode; to provide auniform, low resistivity environment surrounding the anode; and to allow forthe venting of gasses produced at the anode surface.

2.5.2 Direct Current Power Source. The supply of direct electricalcurrent used to develop the potential difference between the anode and thestructure being protected is normally a rectifier which changes alternatingcurrent to direct current of the appropriate voltage and current output. However, in special applications, other direct current power sources such assolar cells, thermoelectric cells, motor-generator sets, and wind-drivengenerators may be used.

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2.5.3 Connection to Structure. Impressed current cathodic protectionanodes are normally supplied with integral lead wires. In impressed currentcathodic protection systems, the anodes are connected to the positive terminalof the rectifier and a wire connection is made between the negative terminalof the rectifier and the structure to be protected. The lead wires areconnected to the cathodic protection system by welding or mechanicalconnections. These should have a low resistance and should be insulated toprevent increased resistance or damage due to corrosion. In applicationswhere multiple anodes are used, the individual anode lead wires are oftenattached to a larger header cable which is connected to the rectifier. As thewire between the rectifier and the anode is under a high positive potential,very rapid attack of the wire will occur where there is a break in the wireinsulation and the wire comes in direct contact with the electrolyte. Theinsulation on this cable is very critical and high quality insulation and carein installation is required for this application.

2.5.4 Other Requirements. As for all systems to be protected, thestructure being protected by impressed current must be electricallycontinuous. The system should also include test stations which are used tomonitor the performance and to adjust the system for proper operation. As inthe case of sacrificial anode systems, impressed current cathodic protectionsystems require periodic inspection, maintenance, and adjustment forsatisfactory operation.

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Section 3: CRITERIA FOR CATHODIC PROTECTION

3.1 Introduction. Various methods are available for determiningwhether the structure to be protected is being effectively protected throughthe application of cathodic protection. The technical basis for corrosion andcathodic protection is electrochemical. Electrochemical methods ofdetermining the effectiveness of cathodic protection systems are the mostwidely used criteria for establishing the adequacy of the protection. Inaddition to electrochemical methods, inspections to determine the actualcondition of the structure being protected can be used to determine whether ornot effective protection has been achieved in the past. If there is no attackof the protected system in an aggressive environment, then the protectivesystem has been functioning adequately. For buried or submerged systems whereaccess is restricted, the electrochemical criteria are most widely applied.

3.2 Electrical Criteria. For submerged and buried structures, criteriabased upon the electrochemical potential of the surfaces of the structure tobe protected are the most widely used criteria for determining whether or notthe structure is being effectively protected. In making these electrochemicalpotential measurements, as shown in Figure 6, a high impedance voltmeter isused to measure the difference in potential between the structure and areference electrode placed in contact with the electrolyte. For buriedstructures, the copper/copper sulphate reference electrode is the referenceelectrode most commonly used for this purpose. For structures submerged inseawater the silver/silver chloride reference electrode is commonly used. Other reference electrodes can be used when appropriate. Potential readingsobtained using any given reference electrode can be related to readingsobtained with other reference electrodes. In order to the assure that thepotential readings obtained are properly interpreted, the reference electrodeused should always be noted. Readings should be reported as "XX.XX V versusYYY" where YYY is the reference electrode used to measure the structurepotential.

As these potential measurements are most commonly used to measurethe potential of buried pipelines they are commonly called "pipe-to-soilpotentials" even though they may refer to the wall of a water storage tank incontact with potable water. The more precise term for these measurements is"structure-to-electrolyte potential."

3.3 Interpretation of Structure-to-Electrolyte Potential Readings. Inorder to determine whether or not a given surface is being adequatelyprotected, structure-to-electrolyte measurements are taken at variouslocations surrounding the structure. Based upon a combination of corrosiontheory, experimental and laboratory tests, and more importantly, upon actualfield experience with a large number of protected structures, criteria forinterpreting these structure-to-electrolyte potentials have been developed.

3.3.1 National Association of Corrosion Engineers (NACE) Standard RP-01-69. The most widely used criteria for evaluating structure-to-electrolytepotentials have been included in the NACE Standard RP-01-69, RecommendedPractice for Control of External Corrosion on Underground or Submerged PipingSystems.

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The following information and criteria are from the 1983 revision of NACERP-01-69.

"Voltage measurements on pipelines are to be made with thereference electrode located on the electrolyte surface as close aspracticable to the pipeline. Such measurements on all other structures ato be made with the reference electrode positioned as close as feasible tthe structure surface being investigated. Consideration should be given voltage (IR) drops other than those across the structure-electrolyteboundary, the presence of dissimilar metals, and the influence of otherstructures for valid interpretation of voltage measurements."

"No one criterion for evaluating the effectiveness of cathodicprotection has proved to be satisfactory for all conditions. Often acombination of criteria is needed for a single structure."

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3.3.1.1 Criteria for Steel. The criteria options for the cathodicprotection of steel and cast iron in soil and water are as follows:

a) -850 mV or more negative with respect to a copper/coppersulfate reference cell. This potential is measured with the protectivecurrent applied. For valid interpretation, the potential measurements must becorrected for IR drop through the electrolyte and metallic paths.

b) 100 mV or greater negative polarization shift measured betweenthe pipe surface and a stable reference electrode contacting the electrolyte. The formation or decay of this polarization can be used in this criterion.

c) A potential at least as negative as the potential establishedby the E log I curve method.

d) A net protective current from the electrolyte into the surfaceof the structure as determined by an earth current technique.

3.3.1.2 Criteria for Aluminum. 100 mV or greater negative polarizationshift (refer to para. 3.3.1.1).

PRECAUTIONARY NOTE

Excessive Voltages: If cathodically protectedat voltages more negative than -1.20 V measuredbetween the structure surface and a saturatedcopper-copper sulfate reference electrodecontacting the electrolyte and compensated forthe voltage (IR) drops other than those acrossthe structure-electrolyte boundary, may suffercorrosion as the result of the build-up ofalkali on the metal surface. A voltage morenegative than -1.20 V should not be used unlessprevious test results indicate no appreciablecorrosion will occur in the particularenvironment.

Alkaline Soil Conditions: Since aluminum maysuffer from corrosion under high pH conditionsand since application of cathodic protectiontends to increase the pH at the metal surface,careful investigation or testing should be madebefore applying cathodic protection to stoppitting attack on aluminum structures inenvironments with a natural pH in excess of8.0.

3.3.1.3 Criteria for Copper. 100 mV or greater negative polarization shift(refer to para 3.3.1.1).

3.3.1.4 Criteria for Dissimilar Metal Structures. A negative potentialequal to that required for the most anodic materials should be maintained. The potential should not exceed the maximum allowable potential for anymaterial (such as for aluminum) in the system.

3.3.2 Other Electrical Criteria. Criteria evaluation of the structure-to-electrolyte potentials on other materials have been developed but are notincluded in NACE RP-01-69. The same measurement techniques and precautionsare applicable to these criteria as for those in NACE RP-01-693.

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3.3.2.1 Criteria for Lead. Criteria for lead shall be as follows:

a) -750 mV or more negative with respect to a copper/coppersulfate reference cell. This potential is measured with the protectivecurrent applied.

b) 100 mV or greater negative polarization shift measured betweenthe pipe surface and a stable reference electrode contacting the electrolyte.

NOTE: With the same precautions regarding potentials over1.2 V and contact with alkaline soils as those foraluminum.

3.3.2.2 NACE RP-02-85. Criteria for the interpretation of structure-to-electrolyte potentials on storage tanks are given in NACE RP-02-85 Control ofExternal Corrosion on Metallic Buried, Partially Buried, or Submerged LiquidStorage Systems. The criteria in this recommended practice refer to theprotection of steel structures and are essentially the same as in NACERP-01-69.

3.4 Failure Rate Analysis. Corrosion damage, as measured by frequencyof system failure, usually increases logarithmically with time after the firstoccurrence of corrosion failure. When effective cathodic protection isapplied to a structure which has experienced corrosion damage, the frequencyof failures will be significantly reduced. However, due to the presence ofexisting corrosion damage, the failure rate will not immediately be reduced tozero. Mechanical damage and previously undetected corrosion related damagemay still result in failure, but if effective cathodic protection is achieved,corrosion failures should cease after a period of 1 or 2 years. Accuratefailure records should be kept for both protected and unprotected systems inorder to determine the need for cathodic protection and the effectiveness ofinstalled systems. A typical failure rate analysis is shown in Figure 7.

3.5 Nondestructive Testing of Facility. Periodic evaluation of thecondition of the protected system can also be used to determine the adequacyof the cathodic protection system installed on the structure, or to establishthe need for protection.

3.5.1 Visual Analysis. If the surface of a structure is accessible or isexposed for repairs, alterations, or specifically for the purposes ofinspection, visual inspection may be used to evaluate the need for protectionof the effectiveness of cathodic protection applied to the structure. Signs ofcorrosion such as the presence of corrosion products, pitting, cracking,reduction in physical size, or other evidence of deterioration should benoted.

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A variation of visual inspection is the installation of smallmetal samples, or coupons, electrically connected to the structure atvarious critical points on the structure. Periodic removal and evaluatioof these samples including visual observation and weight loss can be usedinfer the corrosion activity of the structure being monitored.

3.6 Consequences of Underprotection. If the measured potentials ostructure are not as negative as required by one or more of the applicablcriteria for cathodic protection, some corrosion of the structure may occHowever, the corrosion of the structure will be reduced in proportion to amount of current supplied. When only parts of the structure do not reacthe

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When protective currents are totally interrupted, corrosion willusually return to a normal rate after a short period of time.

3.7 Consequences of Overprotection. In addition to the chemicalcorrosion damage that can occur on aluminum and lead structures if limitingpotentials are exceeded in the negative direction, excessive negativepotentials can also damage other metals. In addition to being wasteful ofanode material or electrical power, excess potentials can cause disbondment ofprotective coatings and can cause hydrogen embrittlement of certain types ofsteels, especially high strength steels.

3.7.1 Coating Disbondment. Excess cathodic protection potentials canresult in the generation of hydrogen gas. When the cathodic protectionpotential reaches the polarized potential of -1.12 V (instant off), withrespect to a copper/copper sulfate reference electrode, the generation ofhydrogen gas will occur. When hydrogen gas is generated it is often trappedbetween the coating and the surface and causes blisters and disbonding of thecoating.

Electrolyte can subsequently fill the gap between the coating andthe metal and, as the coating is an electrical insulator, sufficient currentfor effective cathodic protection cannot reach the affected area and corrosionwill occur. Coating disbondment is a particular problem in water tanks. Insoil environments when high quality coatings are used, disbondment is seldomencountered at potentials less negative than -1.6 V (current on) or -1.12polarized potential (instant off).

3.7.2 Hydrogen Embrittlement. The hydrogen produced when cathodicprotection currents are excessive can also result in the reduction of theductility of steel. This is particularly true for high strength steels (inexcess of 130,000 pounds per square inch (psi) yield strength).

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Section 4: CATHODIC PROTECTION SYSTEM DESIGN PRINCIPLES

4.1 Introduction. As cathodic protection is applied to the preventionof corrosion of a wide variety of structures in a wide variety ofenvironments, each situation will require special consideration. There arefundamental procedures that should be followed in each case. However, theactual functioning of any cathodic protection system is dependent upon thecondition of the local environment at each point on the surface of thestructure to be protected, and upon the actual level of protective currentsupplied to each point of the structure. A predesign survey, as outlined inAppendix A, is essential for determining environmental and structuralconsiderations for the design of any cathodic protection system. While a goodapproximation of the system requirements can be obtained through field surveysand a good approximation of current distribution can be made when allowancesare made for differing environments and interfering structures, the installedsystem will, at a minimum, require initial adjustments to balance the systemand periodic adjustments to maintain that balance. In some cases,particularly in the case of previously unknown interfering metallic structuresin the vicinity of the structure being protected, modifications to theinitially designed system may be required in order to achieve adequateprotection. The design and operation of cathodic protection systems is aniterative procedure.

4.2 General Design Procedures. The general design procedure for bothsacrificial anode and impressed current systems is similar. First the amountof protective current is determined, then the best means of applying thecurrent to the structure is established. In many cases both sacrificial andimpressed current systems are feasible and an initial approximate design isprepared for each type of system in order to select the most appropriate typeof system for the particular application.

4.2.1 Drawings and Specifications. A review of pertinent drawings andspecifications for the structure being protected and for the site should bemade in order to obtain information necessary for the design of a cathodicprotection system. Actual conditions ("As-Built") should be verified sincestructurally and operationally insignificant factors, such as contact betweenburied structures (shorts), can have a great effect upon the operation of acathodic protection system.

4.2.1.1 Drawings and Specifications for the Structure to be Protected. Thesize, shape, material, and surface condition of the structure to be protectedmust be established in order to design an effective cathodic protectionsystem. The size and shape are usually established by the appropriatedrawings for the installation. The material and surface conditions,particularly the presence and quality of protective coatings, are usuallyestablished by the specifications for the installation. For a previouslyinstalled system, the condition of the protective coatings may have to beestablished during a field survey.

4.2.1.2 Site Drawings. A site drawing including all other metallicstructures in the vicinity should also be reviewed to establish the presenceand locations of other structures which may affect the operation of the systembeing designed.

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The presence of other cathodic protection systems in the area should beparticularly noted as the installation of an additional cathodic protectionsystem can affect the operation of existing systems. The review of the sitedrawings should also include the location of sources of ac power for impressedcurrent systems and possible location of anode ground beds.

4.2.2 Field Surveys. A field survey at the site is usually required inorder to establish the actual environmental conditions which will beencountered. For submerged systems, all that is normally required is a wateranalysis, or current requirement test, and a site survey to establish thepresence of interfering structures or other special circumstances. For buriedsystems, more extensive information is required.

4.2.2.1 Water Analysis. Samples of water should be analyzed for pH,chloride, sulfate, and resistivity at a minimum. Other factors such ashardness may be pertinent to the specific circumstance.

4.2.2.2 Soil Characteristics. For buried systems, soil characteristicsmust be defined in order to establish the requirements for protection. Sulfide, sulfate, chloride, pH, and other chemical constituents will affectthe current requirements necessary for protection and protection criteria forsome materials. Current requirements for typical environments are given inTables 1 and 2. Protection criteria are given in para. 3.3.

Table 1Current Requirements for Cathodic Protection of Bare Steel

ENVIRONMENT MILLIAMPERES PER

SQU