MILITARY HANDBOOK: ELECTRICAL ENGINEERING CATHODIC

2,53

MB

PROTECTION

313

stron

6368

ID

UNITED STATES ARMY CORPS OF ENGINEERS

1990

rok

CONTENTS

Section 1 INTRODUCTION

1.1 Scope1

1.2 Cancellation1

1.3 Related Technical Documents1

Section 2 CATHODIC PROTECTION CONCEPTS

2.1 Corrosion as an Electrochemical Process3

2.1.1 Driving Force3

2.1.2 The Electrochemical Cell3

2.1.2.1 Components of the Electrochemical Cell3

2.1.2.2 Reactions in an Electrochemical Cell3

2.2 The Electrochemical Basis for Cathodic Protection4

2.2.1 Potentials Required for Cathodic Protection4

2.3 Practical Application of Cathodic Protection5

2.3.1 When Cathodic Protection Should Be Considered5

2.3.1.1 Where Feasible5

2.3.1.2 When Indicated By Experience5

2.3.1.3 As Required By Regulation5

2.3.2 Functional Requirements for Cathodic Protection 8

2.3.2.1 Continuity8

2.3.2.2 Electrolyte8

2.3.2.3 Source of Current8

2.3.2.4 Connection to Structure8

2.4 Sacrificial Anode Systems8

2.4.1 Anode Materials9

2.4.2 Connection to Structure10

2.4.3 Other Requirements10

2.5 Impressed Current Systems10

2.5.1 Anode Materials10

2.5.2 Direct Current Power Source10

2.5.3 Connection to Structure10

2.5.4 Other Requirements11

Section 3 CRITERIA FOR CATHODIC PROTECTION

3.1 Introduction13

3.2 Electrical Criteria13

3.3 Interpretation of Structure-to-Electrolyte Potential Readings13

3.3.1 National Association of Corrosion Engineers (NACE)Standard RP-01-6913

3.3.1.1 Criteria for Steel15

3.3.1.2 Criteria for Aluminum15

3.3.1.3 Criteria for Copper15

3.3.1.4 Criteria for Dissimilar Metal Structures15

3.3.2 Other Electrical Criteria15

3.3.2.1 Criteria for Lead16

3.3.2.2 NACE RP-02-8516

3.4 Failure Rate Analysis16

3.5 Nondestructive Testing of Facility16

3.5.1 Visual Analysis16

3.6 Consequences of Underprotection17

3.7 Consequences of Overprotection18

3.7.1 Coating Disbondment18

3.7.2 Hydrogen Embrittlement18

Section 4 CATHODIC PROTECTION SYSTEM DESIGN PRINCIPLES

4.1 Introduction19

4.2 General Design Procedures19

4.2.1 Drawings and Specifications19

4.2.1.1 Drawings and Specifications for the Structure to be Protected19

4.2.1.2 Site Drawings19

4.2.2 Field Surveys20

4.2.2.1 Water Analysis20

4.2.2.2 Soil Characteristics20

4.2.2.3 Current Requirement Tests21

4.2.2.4 Location of Other Structures in the Area22

4.2.2.5 Availability of ac Power22

4.2.3 Current Requirements22

4.2.4 Choice of Sacrificial or Impressed Current System22

4.2.5 Basic Design Procedure for Sacrificial Anode Systems23

4.2.6 Basic Design Procedure for Impressed Current Systems24

4.2.6.1 Total Current Determination24

4.2.6.2 Total Resistance Determination26

4.2.6.3 Voltage and Rectifier Determination27

4.2.7 Analysis of Design Factors28

4.3 Determination of Field Data28

4.3.1 Determination of Electrolyte Resistivity 29

4.3.1.1 In Soils29

4.3.1.2 Liquids29

4.3.2 Chemical Analysis of the Environment 31

4.3.2.1 pH31

4.3.3 Coating Conductance31

4.3.3.1 Short Line Method33

4.3.3.2 Long Line Method33

4.3.4 Continuity Testing35

4.3.4.1 Method 135

4.3.4.2 Method 235

4.3.4.3 Method 335

4.3.5 Insulation Testing35

4.3.5.1 Buried Structures35

4.3.5.2 Aboveground Structures38

4.4 Corrosion Survey Checklist38

Section 5 PRECAUTIONS FOR CATHODIC PROTECTION SYSTEM DESIGN

5.1 Introduction39

5.2 Excessive Currents and Voltages39

5.2.1 Interference39

5.2.1.1 Detecting Interference41

5.2.1.2 Control of Interference - Anode Bed Location43

5.2.1.3 Control of Interference - Direct Bonding43

5.2.1.4 Control of Interference - Resistive Bonding45

5.2.1.5 Control of Interference - Sacrificial Anodes47

5.2.2 Effects of High Current Density47

5.2.3 Effects of Electrolyte pH47

5.3 Hazards Associated with Cathodic Protection49

5.3.1 Explosive Hazards49

5.3.2 Bonding for Electrical Safety49

5.3.3 Induced Alternating Currents50

Section 6 IMPRESSED CURRENT SYSTEM

6.1 Advantages of Impressed Current Cathodic Protection Systems53

6.2 Determination of Circuit Resistance53

6.2.1 Anode-to-Electrolyte Resistance53

6.2.1.1 Effect on System Design and Performance53

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 Situations55

6.2.1.5 Field Measurement57

6.2.1.6 Effect of Backfill58

6.2.2 Structure-to-Electrolyte Resistance59

6.2.3 Connecting Cable Resistance59

6.2.4 Resistance of Connections and Splices59

6.3 Determination of Power Supply Requirements59

6.4 Selection of Power Supply Type60

6.4.1 Rectifiers60

6.4.2 Thermoelectric Generators60

6.4.3 Solar60

6.4.4 Batteries60

6.4.5 Generators60

6.5 Rectifier Selection60

6.5.1 Rectifier Components61

6.5.1.1 Transformer Component61

6.5.1.2 Rectifying Elements61

6.5.1.3 Overload Protection61

6.5.1.4 Meters63

6.5.2 Standard Rectifier Types 63

6.5.2.1 Single-Phase Bridge63

6.5.2.2 Single-Phase Center Tap63

6.5.2.3 Three-Phase Bridge63

6.5.2.4 Three-Phase Wye65

6.5.2.5 Special Rectifier Types 65

6.5.3 Rectifier Selection and Specifications68

6.5.3.1 Available Features69

6.5.3.2 Air Cooled Versus Oil Immersed69

6.5.3.3 Selecting ac Voltage70

6.5.3.4 dc Voltage and Current Output70

6.5.3.5 Filters70

6.5.3.6 Explosion Proof Rectifiers70

6.5.3.7 Lightning Arresters71

6.5.3.8 Selenium Versus Silicon Stacks71

6.5.3.9 Other Options71

6.5.3.10 Rectifier Alternating Current Rating71