ELECTRICAL ENGINEERING CATHODIC PROTECTION

Section 1 INTRODUCTION
1.1 Scope. ........................... 1
1.2 Cancellation. ........................ 1
1.3 Related Technical Documents. ................ 1
Section 2 CATHODIC PROTECTION CONCEPTS
2.1 Corrosion as an Electrochemical Process. .......... 3
2.1.1 Driving Force. ....................... 3
2.1.2 The Electrochemical Cell. .................. 3
2.1.2.1 Components of the Electrochemical Cell. ........... 3
2.1.2.2 Reactions in an Electrochemical Cell. ............ 3
2.2 The Electrochemical Basis for Cathodic Protection. ...... 4
2.2.1 Potentials Required for Cathodic Protection. ........ 4
2.3 Practical Application of Cathodic Protection. ........ 5
2.3.1 When Cathodic Protection Should Be Considered. ....... 5
2.3.1.1 Where Feasible. ....................... 5
2.3.1.2 When Indicated By Experience. ................ 5
2.3.1.3 As Required By Regulation. ................. 5
2.3.2 Functional Requirements for Cathodic Protection ....... 8
2.3.2.1 Continuity. ......................... 8
2.3.2.2 Electrolyte. ........................ 8
2.3.2.3 Source of Current. ..................... 8
2.3.2.4 Connection to Structure. .................. 8
2.4 Sacrificial Anode Systems. ................. 8
2.4.1 Anode Materials. ...................... 9
2.4.2 Connection to Structure. .................. 10
2.4.3 Other Requirements. ..................... 10
2.5 Impressed Current Systems. ................. 10
2.5.1 Anode Materials. ...................... 10
2.5.2 Direct Current Power Source. ................ 10
2.5.3 Connection to Structure. .................. 10
2.5.4 Other Requirements. ..................... 11

Section 3 CRITERIA FOR CATHODIC PROTECTION
3.1 Introduction. ........................ 13
3.2 Electrical Criteria. .................... 13
3.3 Interpretation of Structure-to-Electrolyte
Potential Readings. ..................... 13
3.3.1 National Association of Corrosion Engineers (NACE)Standard RP-01-69. ......... 13
3.3.1.1 Criteria for Steel. ..................... 15
3.3.1.2 Criteria for Aluminum. ................... 15
3.3.1.3 Criteria for Copper. .................... 15
3.3.1.4 Criteria for Dissimilar Metal Structures. .......... 15
3.3.2 Other Electrical Criteria. ................. 15
3.3.2.1 Criteria for Lead. ..................... 16
3.3.2.2 NACE RP-02-85. ....................... 16
3.4 Failure Rate Analysis. ................... 16
3.5 Nondestructive Testing of Facility. ............. 16
3.5.1 Visual Analysis. ...................... 16
3.6 Consequences of Underprotection. .............. 17
3.7 Consequences of Overprotection. ............... 18
3.7.1 Coating Disbondment. .................... 18
3.7.2 Hydrogen Embrittlement. ........... ........ 18

Section 4 CATHODIC PROTECTION SYSTEM DESIGN PRINCIPLES
4.1 Introduction. ........................ 19
4.2 General Design Procedures. ................. 19
4.2.1 Drawings and Specifications. ................ 19
4.2.1.1 Drawings and Specifications for the Structure to be Protected. ...... 19
4.2.1.2 Site Drawings. ....................... 19
4.2.2 Field Surveys. ....................... 20
4.2.2.1 Water Analysis. ....................... 20
4.2.2.2 Soil Characteristics. .................... 20
4.2.2.3 Current Requirement Tests. ................. 21
4.2.2.4 Location of Other Structures in the Area. .......... 22
4.2.2.5 Availability of ac Power. .................. 22
4.2.3 Current Requirements. .................... 22
4.2.4 Choice of Sacrificial or Impressed Current System. ...... 22
4.2.5 Basic Design Procedure for Sacrificial Anode Systems. ... 23
4.2.6 Basic Design Procedure for Impressed Current Systems. .... 24
4.2.6.1 Total Current Determination. ................ 24
4.2.6.2 Total Resistance Determination. ............... 26
4.2.6.3 Voltage and Rectifier Determination. ............ 27
4.2.7 Analysis of Design Factors. ................. 28
4.3 Determination of Field Data. ................ 28
4.3.1 Determination of Electrolyte Resistivity .......... 29
4.3.1.1 In Soils. .......................... 29
4.3.1.2 Liquids. .......................... 29
4.3.2 Chemical Analysis of the Environment ............ 31
4.3.2.1 pH. ............................. 31
4.3.3 Coating Conductance. .................... 31
4.3.3.1 Short Line Method. ..................... 33
4.3.3.2 Long Line Method. ...................... 33
4.3.4 Continuity Testing. ..................... 35
4.3.4.1 Method 1. .......................... 35
4.3.4.2 Method 2. .......................... 35
4.3.4.3 Method 3. .......................... 35
4.3.5 Insulation Testing. ..................... 35
4.3.5.1 Buried Structures. ..................... 35
4.3.5.2 Aboveground Structures. ................... 38
4.4 Corrosion Survey Checklist. ................. 38

Section 5 PRECAUTIONS FOR CATHODIC PROTECTION SYSTEM DESIGN
5.1 Introduction. ........................ 39
5.2 Excessive Currents and Voltages. .............. 39
5.2.1 Interference. ........................ 39
5.2.1.1 Detecting Interference. ................... 41
5.2.1.2 Control of Interference - Anode Bed Location. ........ 43
5.2.1.3 Control of Interference - Direct Bonding. .......... 43
5.2.1.4 Control of Interference - Resistive Bonding. ........ 45
5.2.1.5 Control of Interference - Sacrificial Anodes. ........ 47
5.2.2 Effects of High Current Density. .............. 47
5.2.3 Effects of Electrolyte pH. ................. 47
5.3 Hazards Associated with Cathodic Protection. ........ 49
5.3.1 Explosive Hazards. ..................... 49
5.3.2 Bonding for Electrical Safety. ............... 49
5.3.3 Induced Alternating Currents. . ............... 50

Section 6 IMPRESSED CURRENT SYSTEM
6.1 Advantages of Impressed Current Cathodic Protection Systems. .... 53
6.2 Determination of Circuit Resistance. ............ 53
6.2.1 Anode-to-Electrolyte Resistance. .............. 53
6.2.1.1 Effect on System Design and Performance. .......... 53
6.2.1.2 Calculation of Anode-to-Electrolyte Resistance ....... 54
6.2.1.3 Basic Equations ....................... 54
6.2.1.4 Simplified Expressions for Common Situations. ........ 55
6.2.1.5 Field Measurement. ..................... 57
6.2.1.6 Effect of Backfill. ..................... 58
6.2.2 Structure-to-Electrolyte Resistance. ............ 59
6.2.3 Connecting Cable Resistance. ................ 59
6.2.4 Resistance of Connections and Splices. ........... 59
6.3 Determination of Power Supply Requirements. ......... 59
6.4 Selection of Power Supply Type. ............... 60
6.4.1 Rectifiers. ......................... 60
6.4.2 Thermoelectric Generators. ................. 60
6.4.3 Solar. ........................... 60
6.4.4 Batteries. ......................... 60
6.4.5 Generators. ......................... 60
6.5 Rectifier Selection. .................... 60
6.5.1 Rectifier Components. .................... 61
6.5.1.1 Transformer Component. ................... 61
6.5.1.2 Rectifying Elements. .................... 61
6.5.1.3 Overload Protection. .................... 61
6.5.1.4 Meters. ........................... 63
6.5.2 Standard Rectifier Types .................. 63
6.5.2.1 Single-Phase Bridge. .................... 63
6.5.2.2 Single-Phase Center Tap. .................. 63
6.5.2.3 Three-Phase Bridge. ..................... 63
6.5.2.4 Three-Phase Wye. ...................... 65
6.5.2.5 Special Rectifier Types ................... 65
6.5.3 Rectifier Selection and Specifications. ........... 68
6.5.3.1 Available Features. ..................... 69
6.5.3.2 Air Cooled Versus Oil Immersed. ............... 69
6.5.3.3 Selecting ac Voltage. .................... 70
6.5.3.4 dc Voltage and Current Output. ............... 70
6.5.3.5 Filters. .......................... 70
6.5.3.6 Explosion Proof Rectifiers. ................. 70
6.5.3.7 Lightning Arresters. .................... 71
6.5.3.8 Selenium Versus Silicon Stacks. ............... 71
6.5.3.9 Other Options. ....................... 71
6.5.3.10 Rectifier Alternating Current Rating. ............ 71
6.6 Anodes for Impressed Current Systems. ............ 73
6.6.1 Graphite Anodes. ...................... 74
6.6.1.1 Specifications. ....................... 74
6.6.1.2 Available Sizes. ...................... 74
6.6.1.3 Characteristics. ...................... 77
6.6.1.4 Operation. ......................... 77
6.6.2 High Silicon Cast Iron. ................... 78
6.6.3 High Silicon Chromium Bearing Cast Iron (HSCBCI). .... 78
6.6.3.1 Specifications. ....................... 78
6.6.3.2 Available Sizes. ...................... 79
6.6.3.3 Operation. ......................... 79
6.6.4 Aluminum. .......................... 79
6.6.5 Platinum. .......................... 79
6.6.6 Platinized Anodes. ..................... 79
6.6.6.1 Types. ........................... 90
6.6.6.2 Operation. ......................... 91
6.6.7 Alloyed Lead. ........................ 91
6.7 Other System Components. .................. 91
6.7.1 Connecting Cables. ..................... 91
6.7.1.1 Factors to be Considered. .................. 91
6.7.1.2 Insulation. ......................... 92
6.7.1.3 Recommended Cables for Specific Applications. ........ 93
6.7.1.4 Economic Wire Size. ..................... 93
6.7.2 Wire Splices and Connections. ................ 94
6.7.3 Test Stations. ....................... 96
6.7.4 Bonds. ........................... 96
6.7.5 Insulating Joints. ................ ..... 96

Section 7 SACRIFICIAL ANODE SYSTEM DESIGN
7.1 Theory of Operation. ................... . 113
7.1.1 Advantages of Sacrificial Anode Cathodic Protection Systems. .... . 113
7.1.2 Disadvantages of Sacrificial Anode Cathodic Protection Systems. ..... . 113
7.2 Sacrificial Anode Cathodic Protection System DesignProcedures. ...... . 113
7.3 Determination of Current Required for Protection. ...................... . 114
7.4 Determination of Anode Output. .............. . 114
7.4.1 Simplified Method for Common Situations. ......... . 114
7.4.2 Determination of Output Using Anode-to-Electrolyte Resistance. ... . 114
7.4.2.1 Calculation of Anode-to-Electrolyte Resistance. ...... . 114
7.4.2.2 Determination of Structure-to-Electrolyte Resistance. .. . 115
7.4.2.3 Connecting Cable Resistance. ............... . 115
7.4.2.4 Resistance of Connections and Splices. .......... . 115
7.4.2.5 Total Circuit Resistance. ................. . 115
7.4.2.6 Anode-to-Structure Potential. ............... . 115
7.4.2.7 Anode Output Current. ................... . 115
7.4.3 Field Measurement of Anode Output. ............ . 116
7.5 Determination of Number of Anodes Required. ........ . 116
7.6 Determination of Anode Life. ............... . 116
7.7 Seasonal Variation in Anode Output. ............ . 117
7.8 Sacrificial Anode Materials ................ . 117
7.8.1 Magnesium. ........................ . 117
7.8.1.1 Composition. ....................... . 118
7.8.1.2 Anode Efficiency. ..................... . 118
7.8.1.3 Potentials. ........................ . 119
7.8.1.4 Sizes. .......................... . 119
7.8.1.5 Current Output. ...................... . 119
7.8.1.6 Backfill. ......................... . 119
7.8.2 Zinc. ........................... . 119
7.8.2.1 Composition. ....................... . 125
7.8.2.2 Anode Efficiency. ..................... . 125
7.8.2.3 Potentials. ........................ . 125
7.8.2.4 Sizes. .......................... . 126
7.8.2.5 Current Output. ...................... . 126
7.8.2.6 Backfill. ......................... . 126
7.8.3 Aluminum. ......................... . 126
7.8.3.1 Composition. ....................... . 127
7.8.3.2 Anode Efficiency. ..................... . 127
7.8.3.3 Potentials. ........................ . 127
7.8.3.4 Sizes. .......................... . 127
7.8.3.5 Current Output. ...................... . 127
7.9 Other System Components .................. . 127
7.9.1 Connecting Wires. ..................... . 127
7.9.1.1 Determination of Connecting Wire Size and Type. ...... . 133
7.9.2 Connections and Splices. ................. . 134
7.9.3 Bonds and Insulating Joints. ............... . 134
7.9.4 Test Station Location and Function. ............ . 134
7.9.5 Backfill. ......................... . 135

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

Section 9 CATHODIC PROTECTION SYSTEM DESIGN EXAMPLES
9.1 Introduction. ....................... . 155
9.2 Elevated Steel Water Tank. ................ . 155
9.2.1 Design Data ........................ . 156
9.2.2 Computations ....................... . 156
9.3 Elevated Water Tank (Where Ice is Expected). ....... . 173
9.3.1 Design Data ........................ . 176
9.3.2 Computations ....................... . 176
9.4 Steel Gas Main. ...................... . 177
9.4.1 Design Data ........................ . 180
9.4.2 Computations ....................... . 180
9.5 Gas Distribution System. ................. . 184
9.5.1 Design Data ........................ . 185
9.5.2 Computations ....................... . 185

Page
9.6 Black Iron, Hot Water Storage Tank. ............ . 187
9.6.1 Design Data ........................ . 188
9.6.2 Computations ....................... . 188
9.7 Underground Steel Storage Tank. .............. . 190
9.7.1 Design Data ........................ . 190
9.7.2 Computations ....................... . 192
9.8 Heating Distribution System. ............... . 192
9.8.1 Design Data ........................ . 192
9.8.2 Computations ....................... . 193
9.8.3 Groundbed Design ..................... . 194
9.8.4 Rectifier Location. .................... . 195
9.9 Aircraft Multiple Hydrant Refueling System. ........ . 195
9.9.1 Design Data ........................ . 195
9.9.2 Computations. ....................... . 196
9.10 Steel Sheet Piling in Seawater (Galvanic nodes). ..... . 199
9.10.1 Design Data ........................ . 199
9.10.2 Computations ....................... . 201
9.11 Steel Sheet Piling in Seawater (Impressed Current
9.11.1 Design Data. ....................... . 203
9.11.2 Computations ....................... . 203
9.12 Steel H Piling in Seawater (Galvanic Anodes). ....... . 207
9.12.1 Design Data ........................ . 208
9.12.2 Computations ....................... . 208
9.13 Steel H Piling in Seawater (Impressed Current). ...... . 210
9.13.1 Design Data ........................ . 210
9.13.2 Computations ....................... . 210

Section 10 INSTALLATION AND CONSTRUCTION PRACTICES
10.1 Factors to Consider. ................... . 213
10.2 Planning of Construction. ................. . 213
10.3 Pipeline Coating. ..................... . 213
10.3.1 Over-the-Ditch Coating. .................. . 213
10.3.2 Yard Applied Coating. ................... . 213
10.3.3 Joint and Damage Repair. ................. . 214
10.3.4 Inspection. ........................ . 214
10.4 Coatings for Other Structures. .............. . 214
10.5 Pipeline Installation. .................. . 214
10.5.1 Casings. ......................... . 214
10.5.2 Foreign Pipeline Crossings. ................ . 215
10.5.3 Insulating Joints. .................... . 215
10.5.4 Bonds. .......................... . 216
10.6 Electrical Connections. .................. . 216
10.7 Test Stations. ...................... . 216
10.8 Sacrificial Anode Installation. .............. . 216
10.8.1 Vertical. ......................... . 216
10.8.2 Horizontal. ........................ . 217
10.9 Impressed Current Anode Installation. ........... . 217
10.9.1 Vertical. ......................... . 219
10.9.2 Horizontal. ........................ . 219
10.9.3 Deep Anode Beds. ..................... . 219
10.9.4 Other Anode Types. .................... . 225
10.9.5 Connections. ....................... . 225
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10.10 Impressed Current Rectifier Installation. ......... . 225
Section 11 SYSTEM CHECKOUT AND INITIAL ADJUSTMENTS
11.1 Introduction. ....................... . 229
11.2 Initial Potential Survey. ................. . 229
11.3 Detection and Correction of Interference. ......... . 229
11.4 Adjustment of Impressed Current Systems. ......... . 229
11.4.1 Uneven Structure-To-Electrolyte Potentials. ........ . 229
11.4.2 Rectifier Voltage and Current Capacity. .......... . 230
11.5 Adjustment of Sacrificial Anode Systems. ......... . 230
11.5.1 Low Anode Current Levels. ................. . 230
11.5.2 Inadequate Protection at Designed Current Levels ..... . 230

Section 12 MAINTAINING CATHODIC PROTECTION
12.1 Introduction. ....................... . 231
12.2 Required Periodic Monitoring and Maintenance. ....... . 231
12.3 Design Data Required for System Maintenance. ....... . 231
12.3.1 Drawings. ......................... . 231
12.3.2 System Data. ....................... . 231
12.3.2.1 Design Potentials. .................... . 231
12.3.2.2 Current Output. ...................... . 231
12.3.2.3 System Settings and Potential Readings. .......... . 231
12.3.2.4 Rectifier Instructions. .................. . 232
12.4 Basic Maintenance Requirements. .............. . 232
12.5 Guidance for Maintenance ................. . 232
12.5.1 Agency Maintenance and Operations Manuals. ........ . 232
12.5.2 DOT Regulations. ..................... . 235
12.5.3 NACE Standards. ...................... . 235

Section 13 ECONOMIC ANALYSIS
13.1 Importance of Economic Analysis. ............. . 237
13.2 Economic Analysis Process. ................ . 237
13.2.1 Define the Objective. ................... . 237
13.2.2 Generate Alternatives. .................. . 238
13.2.3 Formulate Assumptions. .................. . 238
13.2.4 Determine Costs and Benefits. ............... . 238
13.2.4.1 Costs. .......................... . 238
13.2.4.2 Benefits. ......................... . 239
13.2.5 Compare Costs and Benefits and Rank Alternatives. .... . 239
13.2.6 Perform Sensitivity Analysis. ............... . 239
13.3 Design of Cathodic Protection Systems. .......... . 239
13.4 Economic Analysis - Example 1 ............... . 240
13.4.1 Objective. ........................ . 240
13.4.2 Alternatives ....................... . 240
13.4.3 Assumptions ........................ . 240
13.4.4 Cost/Benefit Analysis ................... . 240
13.4.4.1 Cost - Alternative 1--Steel Line Without Cathodic Protection. ... . 240
13.4.4.2 Cost - Alternative 2--Steel Line with Cathodic Protection. ......... . 242
13.4.4.3 Cost - Alternative 3--Plastic Line. ............ . 242
13.4.4.4 Benefits. ......................... . 243
13.4.5 Compare Costs/Benefits .................. . 243
13.5 Economic Analysis - Example 2 ............... . 243
13.5.1 Objective. ........................ . 243
13.5.2 Alternative ........................ . 243
13.5.3 Assumptions ........................ . 243
13.5.4 Cost/Benefit Analysis ................... . 244
13.5.4.1 Cost - Alternative 1--Steel Line Without Cathodic Protection. ... . 244
13.5.4.2 Cost - Alternative 2--Steel Line With Cathodic Protection. ....... . 245
13.5.4.3 Benefits. ......................... . 246
13.5.5 Compare Costs/Benefits .................. . 246
13.5.6 Conclusions and Recommendations. ............. . 247
13.6 Economic Analysis - Example 3 ............... . 247
13.6.1 Objective. ........................ . 247
13.6.2 Alternatives ....................... . 247
13.6.3 Assumptions ........................ . 247
13.6.4 Cost/Benefit Analysis ................... . 247
13.6.4.1 Cost - Alternative 1--Impressed Current Cathodic Protection. ... . 247
13.6.4.2 Cost - Alternative 2--Galvanic Anode System. ....... . 248
13.6.5 Compare Costs/Benefits .................. . 249
13.7 Economic Analysis - Example 4 ............... . 249
13.7.1 Objective ......................... . 249
13.7.2 Alternatives ....................... . 249
13.7.3 Assumptions ........................ . 249
13.7.4 Cost/Benefit Analysis ................... . 249
13.7.4.1 Cost - Alternative 1--Cathodic Protection System Maintenance Continued. .. . 249
13.7.4.2 Cost - Alternative 2--Cathodic Protection System Maintenance Discontinued. . . 250
13.7.5 Compare Benefits and Costs ................ . 251
13.8 Economic Analysis Goal. .................. . 251

Section 14 CORROSION COORDINATING COMMITTEE PARTICIPATION
14.1 Introduction. ....................... . 253
14.2 Functions of Corrosion Coordinating Committees. ...... . 253
14.3 Operation of the Committees. ............... . 253
14.4 Locations of Committees. ................. . 253
APPENDIX
APPENDIX A UNDERGROUND CORROSION SURVEY CHECKLIST .......... . 255
B ECONOMIC LIFE GUIDELINES ................. . 265
C PROJECT YEAR DISCOUNT FACTORS ............... . 267
D PRESENT VALUE FORMULAE .................. . 269
E DOT REGULATIONS ...................... . 271

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