Nace CP 1 - Direction of Survey Travel; Surface Potential Survey

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TM0497-2002

NACE International 23

+xxmV

-xxmV-xxmV-xxmV

+xxmV

CURRENT IN PIPE WALL

DIRECTION OF SURVEY TRAVEL

CATHODIC

AREA

ANODIC

AREA

CATHODIC

AREA

Electrolyte

Current

Electrolyte

Current

UNPROTECTED PIPELINE

v vvv

NOTE: Actual readings are usually 50 mV or less.

As the anodic condition in the center of the figure is passed (traveling left to right), the indicated

polarity switches from positive to negative. This polarity reversal indicates an anodic condition.

FIGURE B1

Surface Potential Survey

Main Page

Default Chapter2
- Acknowledgements2
- Important Notice3
- Cathodic Protection Tester Certification Application4
- Glossary of Terms10
- Examination Results12
- Nace Corrosion Network14
- Cathodic Protection Tester15
- Course Outline15
- The Course16
- Audience (Who Should Attend)17
- Experiments17
- Length17
- Prerequisites17
- Certification Application18
- Quizzes and Examinations18
- Attestation23
- Basic Electricity24
- Electrical Terms24
- Electrons24
- Voltage24
- Common Symbols for Voltage25
- Current25
- Resistance and Resistivity26
- Crossectional Area27
- Typical Resistivity of Common Materials28
- Electrical Schematic Diagram Symbols29
- Ohm’s Law30
- Electrical Laws30
- Basic DC Electrical Circuit30
- Electric Circuit30
- Current through a Resistor31
- Power32
- What Is the Current Flow?32
- Current Law33
- Kirchhoff’s Laws33
- Kirchhoff’s Voltage Law33
- Voltage Law33
- Kirchhoff’s Current Law34
- Series Circuit34
- Parallel Circuit36
- Series-Parallel Circuit38
- Series and Parallel Circuits Combined39
- Typical Alternating Current41
- Alternating Current (AC)41
- Pure Direct Current41
- Direct Current (DC)41
- DC Produced by Rectifying AC42
- Transformers42
- Impedance43
- Typical Transformer Wiring in a Rectifier43
- Meter Operation44
- Analog Meters45
- Basic Meter Movement45
- D'arsonval Movement (Voltmeter)46
- Ammeters47
- Ohmmeters47
- Voltmeters47
- Meter Hook up48
- Digital Meters48
- Basis of Operation48
- Resistor and Instrument Lab52
- Data Sheet54
- Diode Check55
- Measured Voltage Drops55
- Meter Fuses – Instructions for Replacement56
- Color Code for Resistors57
- Atoms58
- Basic Chemistry58
- Elements58
- Compounds (Molecules)59
- Ions59
- The Bohr Model of an Atom59
- Water Molecule60
- Acidity and Alkalinity (Ph)60
- Illustration of Acid and Alkaline Ph61
- Basic Electrochemistry62
- Effect of Ph on the Rate of Corrosion62
- Anodic Process (Half Reaction)63
- Oxidation63
- Cathodic Process (Half Reaction)64
- Reduction64
- Electrochemical Circuits65
- Electrolyte65
- Ionization65
- Anode Reactions66
- Corrosion Cell66
- Cathode Reactions67
- Typical Local Action Corrosion Cells on a Structure67
- External Circuit68
- Charge Transfer in the Electrolyte68
- Electron and Ion Flow68
- A Voltmeter Connection Is a Parallel Connection69
- Conventional Current Flow69
- Use of Voltmeters69
- Voltmeter Hook up69
- Current Direction70
- Polarity Sign70
- Sign Convention71
- Copper-Copper Sulfate Electrode72
- Reference Electrodes (Half-Cells)72
- Copper-Copper Sulfate Reference Electrode in Contact with Earth73
- Portable Copper-Copper Sulfate Reference Electrodes73
- Use and Care of Copper Sulfate Reference Electrodes74
- Elevation Difference Causes Water to Flow75
- Driving Force for Corrosion75
- Consumption Rate (K) for Various Metals76
- Corrosion Rate76
- Faraday’s Law76
- Polarization77
- Anode/Cathode Ratio78
- Factors that Affect the Corrosion Rate78
- Influence of the Environment78
- Moisture Content78
- Chemical Activity79
- Conductivity79
- Causes of Corrosion80
- Dissimilar Metals (Galvanic Corrosion)80
- Naturally Occurring Corrosion80
- Practical Galvanic Series81
- Alloying82
- Flashlight Battery as an Example of a Galvanic Cell82
- Graphite-Zinc Battery82
- Mechanical Stresses82
- Dissimilar Soils83
- Metal Ion Concentration Cell83
- Oxygen Concentration Cell83
- Temperature Differences in the Electrolyte83
- Metal Electrode Potentials in Tap Wate84
- Conclusions85
- Results85
- Corrosion-Cell86
- Potential Measurement87
- Polarized Potential Measurement88
- Current Direction in the External Circuit in Corrosion Cell89
- Experiment 2.3 Current Direction in the Electrolyte in Corrosion Cells92
- Reference Cell Maintenance94
- Conversions and Definitions96
- U.S. Customary/Metric Conversions98
- Materials Selection99
- Protective Coatings99
- Underground Corrosion Control99
- Underground or Submerged Structures99
- Bituminous Enamels100
- Exposure to Sunlight100
- Extruded Polyolefin and Polyethylene100
- Types of Mill Applied Underground Coatings100
- Two-Component Liquid Resin Coatings101
- Surface Preparation101
- Application101
- Girth Weld and Other Field Coatings101
- Electrical Isolation102
- Environmental Control102
- Maintenance Inspections102
- Adjustment of Ph103
- Inhibitors103
- Maintenance of Environmental Control103
- Cathodic Protection104
- Microscopic Corrosion Cell104
- Theory104
- Cathodic Protection on a Structure105
- Definition105
- Structures that Can be Cathodically Protected106
- Typical Galvanic Anode Cathodic Protection107
- Anodes107
- Galvanic Anode Systems107
- Applications of Galvanic Anode Systems108
- Advantages of Galvanic Anodes109
- Component Parts of Galvanic Systems109
- Limitations of Galvanic Anodes109
- Magnesium109
- Aluminum110
- Galvanic Anode Efficiency110
- Zinc110
- Attachment to Structures111
- Backfill111
- Size and Shapes111
- Specifications of Galvanic Anode Systems111
- Typical Impressed Current Cathodic Protection112
- Impressed Current Systems112
- Applications of Impressed Current Cathodic Protection113
- Power Sources113
- Advantages of Impressed Current Systems114
- Component Parts of Impressed Current Systems114
- Graphite114
- Limitations of Impressed Current Systems114
- Mixed Metal Oxide115
- Platinum115
- Conductive Polymer116
- Lead-Silver116
- Power Supply116
- Scrap Metal116
- Solar Panels117
- Cathodic Protection Rectifier Schematic117
- Engine-Generator Units118
- Wind Powered Generator Installation118
- Wind Powered Generators118
- Electrical Connections119
- Thermoelectric Generators119
- Coating120
- Factors Influencing Operation of Cathodic Protection120
- Moisture Content of Soil120
- Soil Texture120
- Glacial Till121
- Movement of Structure and Electrolyte121
- Oxygen Content121
- Temperature121
- Metal122
- Electrical Shielding122
- Make up of the Electrolyte122
- Cathodic Shielding Due to a Shorted Casing122
- Criteria for Cathodic Protection123
- Dielectric123
- NACE International Recommended Criteria123
- Ir Drop124
- Resistances124
- Voltage Drops in a Measuring Circuit124
- Recommended Criteria126
- Underground or Submerged Iron and Steel126
- Application of These Criteria127
- Structure-To-Electrolyte Potentials127
- Underground or Submerged Aluminum and Copper Piping128
- Offshore Platforms in Salt Water128
- Dissimilar Metal Situations128
- Above Ground Storage Tanks129
- Interiors of Steel Water Storage Tanks129
- Oil Heater-Treaters129
- Canada130
- International Standard ISO 15589-1130
- Steel Reinforced Concrete130
- Demonstrate Change in Polarized Potential with Time136
- Experiment to Demonstrate Change in Polarized Potential with Time136
- Safety138
- Safety Analysis Prior to Commencing Project138
- Electrical139
- Electrical Equipment (Rectifier) Case139
- Electrical Equipment (Rectifiers)139
- Cathodic Protection (CP) Rectifiers140
- Lock out / Tag out141
- Electrical Hazardous Areas142
- Explosions or Ignitions142
- Group Scissor Lock out / Tag out (LOTO)142
- Cathodic Protection Surveys143
- Induced AC Voltages144
- Excavations145
- Hazardous Material145
- Material Safety Data Sheets (MSDS)145
- Other General Precautions146
- Reaction Products146
- Calomel Reference Electrode148
- Field Measurements148
- Other Portable Reference Electrodes148
- Silver-Silver Chloride Reference Electrode148
- Stationary Reference Electrodes149
- Sulfate Reference Electrode149
- Basis of Measurement150
- Structure–To–Electrolyte Potential150
- Typical Applications150
- Voltmeter Ranges150
- Close Interval Potential Survey151
- Location of Reference Electrode151
- Pipe-To-Soil Potential Profile152
- Earth Current Flow and Surface Potential Measurements153
- Potential Measurement between Two Reference Electrodes153
- Recording Voltmeters153
- Voltage (IR) Drop in Potential Data153
- X-Y Plotters154
- Strip Chart Recorders154
- Data Loggers154
- Ammeter Connection155
- Measuring Current155
- Series Connection155
- Use of an Ammeter155
- Current Flow Sign156
- Current Range156
- Direction of Current Flow in an Ammeter Measurement156
- Clamp-On Ammeters157
- Shunts157
- Current Calculation158
- Shunt Measurement158
- Direction of Current Flow159
- Shunt Types and Values161
- Galvanic Anode Output162
- Current Flow on a Pipeline or Cable163
- Current Requirement Tests163
- Rectifier Current Output163
- 2-Wire Line Current Test164
- Steel Pipe Resistance166
- Table of Pipe Resistances166
- 4-Wire Line Current Test167
- Bond Current169
- Measuring Resistance169
- Typical Measurements169
- Using Ohm’s Law169
- Isolation Joint Test Using an Ohmmeter170
- Using an Ohmmeter170
- Purpose and Usage171
- Electrical Continuity171
- Accidental Contacts172
- Isolation (Insulating) Joints172
- Measuring Structure Continuity173
- Methods for Testing an Isolation Fitting Include173
- Testing Resistance between a Pipe and Casing173
- Diode Bias174
- Four-Pin (Wenner) Method of Measuring Soil Resistivity175
- Measuring Electrolyte Resistivity175
- Wenner Four-Pin Method175
- Average and Layer Resistivity176
- Resistivity Soil Box177
- Soil Box177
- Single Probe Soil Resistivity Measurement178
- Resistivity Probe178
- Measuring Ph178
- Use of Pipe Locating Devices179
- Conductive180
- Conductive Pipe Locator Principle180
- Example of a Conductive Pipe Locator181
- Inductive181
- Inductive Pipe Locator Principle181
- Coupon Measurements182
- Current Interrupter182
- Use of Current Interrupters182
- Definitions184
- Effects184
- Sources184
- Types of Stray Current185
- Steady State Stray Current185
- Dynamic Stray Current185
- Measurement Indications186
- Proximity of Possible Sources186
- Recording of Dynamic Stray Currents186
- Identification of Stray Current186
- Location of Foreign Structures and Rectifiers188
- Pipe-To-Soil Data Plot Indicating Cathodic Interference188
- Mitigation Bonds189
- Stray Current Corrosion Control189
- Mitigation with Cathodic Protection191
- Demonstration of Cathodic Interference192
- Reasons for Monitoring194
- Monitoring Cathodic Protection195
- Monitoring Requirements195
- Technical197
- Date, Time, and Weather197
- Recordkeeping197
- Importance of Good Record Keeping197
- Computer Records and Spreadsheets198
- Facility Maps and Work Documentation198
- Site Conditions198
- Sketches198
- Test Stations200
- Construction Notes201
- Environmental Factors201
- Types of Test Stations202
- Typical Post Mounted Potential Measurement Test Station202
- IR (Millivolt) Drop (Current Span)203
- Typical Flush Mounted Potential Measurement Test Station203
- Pipe Casing204
- IR Drop Test Station204
- Casing Test Station205
- Foreign Line Crossing205
- Foreign Line Crossing Test Station206
- Isolating Joint206
- Isolating Coupling207
- Isolating Union207
- Isolating Flange208
- Properly Isolated Casing208
- Coupons209
- Isolation Joint Test Station Mitigation Bond209
- Typical Coupon Test Station210
- Thermite (Exothermic) Welding211
- Wire Attachment211
- Thermite Weld Process212
- Galvanic (Sacrificial) Anodes213
- Mechanical213
- Prepackaged Anodes214
- Multiple Prepackaged Vertical Anodes215
- Single Prepackaged Vertical Anode215
- Bracelet Anodes216
- Non Packaged Anodes216
- Ribbon or Strip Anodes216
- Offshore Anodes217
- Typical Bracelet Anode217
- Aluminum Alloy Anodes for Offshore Structures218
- Impressed Current Groundbeds218
- Handling and Inspection of Anodes and Cable219
- Prepackaged Impressed Current Anode220
- Surface Groundbed Configurations221
- Vertical Anode Installation221
- Horizontal Anode Installation222
- Header Cable Installation223
- Horizontal Impressed Current Anode223
- Distributed Anode Configuration224
- Surface Remote Groundbed Configuration224
- Deep Anode Groundbed Configuration225
- Distributed Anode Groundbed Protecting Wharf Piling225
- Surface Distributed Anode Groundbed Configuration225
- Deep Anode Installation227
- Negative Circuit227
- Installation of Rectifiers or Other Power Sources228
- Rectifiers228
- DC Output229
- Anode Circuit (Positive Circuit)229
- AC Power and Wiring229
- Troubleshooting230
- Current Profile231
- Illustration of Shorted Structure231
- Testing a Pipeline231
- Locating a Short through Current Flow232
- Tone Generator232
- Casing Shorts233
- Using Audio Tone Locator to Find Shorts233
- Resistance Testing between a Casing and a Pipeline234
- Isolating Joint Shorts235
- Resistance Test Set-Up for an Isolating Joint235
- Cathodic Protection Levels236
- Improper Backfill237
- Galvanic and Impressed Current Groundbeds237
- Groundbed Malfunctions237
- Anode Deterioration237
- Drying of Soil238
- Routine Maintenance238
- Output Problems239
- Zero Current and Voltage Outputs239
- Locating a Short Circuit in a Rectifier Circuit240
- Significant Changes in both Voltage and Current Outputs241
- Significant Current Change with Unchanged Voltage241
- Zero Current Output with Unchanged Voltage Output241
- Appended Documents242
- Primary Reference244
- Nace Glossary of Corrosion-Related Terms247
- Reference Electrode Classifications265
- Element Types265
- Factors Affecting the Accuracy of Reference Electrodes265
- Electrolyte Types265
- External Influences266
- Lights Effects266
- Reference Potential266
- Temperature Effects266
- Contamination Effects267
- Design Life of Permanent Cells267
- Electrolyte Concentration Effects267
- References268
- Standard Recommended Practice269
- Table of Contents271
- NACE International Standard Recommended Practice271
1 General272
2 Definitions272
3 Determination of Need for External Corrosion Control274
- Economic Factors Include the Following274
4 Piping System Design275
- External Corrosion Control275
- Corrosion Control Test Stations276
5 External Coatings277
- Storage, Handling, Inspection, and Installation278
6 Criteria and Other Considerations for Cathodic Protection283
- Criteria for Copper286
- Criteria for Aluminum286
- Criteria for Steel and Cast Iron286
- Additional References286
- Bibliography for Section 6286
7 Design of Cathodic Protection Systems288
- Design Drawings and Specifications291
- Bibliography for Section 7291
8 Installation of Cathodic Protection Systems292
- Construction Specifications292
- Construction Supervision292
- Installing Anodes292
9 Control of Interference Currents293
- Mechanism of Interference-Current Corrosion293
10 Operation and Maintenance of Cathodic Protection Systems295
11 External Corrosion Control Records296
- Installation of Interference Mitigation Facilities297
- References298
Appendix A-Interference Testing299
Appendix B-Method for Determining Probable Corrosion Rate and Costs of Maintaining Service300
Appendix C-Contingent Costs of Corrosion300
Appendix B-Costs of Corrosion Control300
- Recommended Practice302
- NACE International Standard304
- Definitions305
- General305
- Cathodic Protection of New UST Systems306
- Structures in Selected Oil Provinces356
Appendix A-Typical Design Parameters for Offshore Petroleum Production356
- Design Criteria for Cathodic Protection Systems358
- Resistivities (Ohm-CM) Temperature358
- A1: Current Density/Temperature Curves359
Appendix B-Energy Capabilities and Consumption Rates of Various Commercial Galvanic Anodes Available for Cathodic Protection of Offshore Structures359
Appendix C-Consumption Rates in Seawater of Various Commercial Types of Impressed Current Anodes Available for Cathodic Protection of Offshore Structu360
Appendix D-Typical Method for Calculation of Galvanic Anode Current Output Using Initial, Maintenance, and Final Current Densities360
Appendix E-Typical Method of Calcuation of Galvanic Anode Current Output Using Design Slope and Maintenance Current Density362
- Seawater362
- General367
- Definitions367
- Determination of the Need for Cathodic Protection368
Appendix A-Wire Gauge Conversions395
- Human Resistance to Electrical Curren389
- Internal Cathodic Protection Systems in Oil-Treating Vessels396
- Definitions399
- General399
- Design and Selection of Cathodic Protection System400
- Determination of Need for Cathodic Protection400
- Anode Installation402
Appendix A-Glossary of Terms452
Appendix B-Additional Information Useful for Design453
Appendix C-Test Equipment454
- Steel-Cased Pipeline Practices455
- Definitions458
- Design458
- General458
- Installation459
- Maintenance and Repair461
- Monitoring462
- Bibliography463
- References463
Appendix A: Typical Casing-Filling Procedures464
Appendix B: Monitoring Techniques465
- Establishing a Circuit for a Four-Wire IR Drop Test469
- Four-Wire IR Drop Test469
- Establishing the Circuit (Downstream [D/S] End)470
- Alternate Method: Lineal Conductance Values for the Casing472
- Casing Depolarization Test472
- Cycling the Rectifier472
- Casing Clear473
- Casing Shorted473
- Use of Pipe/Cable Locator474
- Pipe Data475
- Standard Test Method478
- NACE International Standard Test Method480
- Definitions481
- General481
- Instrumentation and Measurement Guidelines483
- Safety Considerations483
- Instrument Accuracy484
- Pipe-To-Electrolyte Potential Measurements484
Appendix A: Reference Electrodes498
- Measurement Techniques for Net Protective Current499
- Two-Reference-Electrode Surface Survey499
Appendix B: Net Protective Current499
- Pipe-To-Electrolyte Potential Survey501
- Cathodic Protection Using the Net Protective Current Technique502
- Direction of Survey Travel503
- Surface Potential Survey503
Appendix C: Using Coupons to Determine Adequacy of Cathodic Protection505
- Definitions512
- General512
- Instrumentation and Measurement Guidelines514
- Safety Considerations514
- Tank-To-Electrolyte Potential Measurements515
Appendix A: Using Coupons to Determine the Adequacy of Cathodic Protection532

Nace CP 1 - Direction of Survey Travel; Surface Potential Survey

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