Page 12 - Corrosion Engineering Principles and Practice

x C o n t e n t s C o n t e n t s xi

13.3 How Cathodic Protection Works in Soils . . . 532
13.3.1 Sacrificial Cathodic Protection . . . . 536
13.3.2 Impressed Current
Cathodic Protection . . . . . . . . . . . . . 536
13.3.3 Anode Beds . . . . . . . . . . . . . . . . . . . . 538
13.3.4 Anode Backfill . . . . . . . . . . . . . . . . . . 540
13.4 How Cathodic Protection
Works in Concrete . . . . . . . . . . . . . . . . . . . . . . 544
13.4.1 Impressed Current
Cathodic Protection . . . . . . . . . . . . . 545
13.4.2 Sacrificial Cathodic Protection . . . . 548
13.5 Cathodic Protection Components . . . . . . . . . 550
13.5.1 Reference Electrodes . . . . . . . . . . . . 550
13.5.2 Anodes . . . . . . . . . . . . . . . . . . . . . . . . 553
13.5.3 Rectified Current Sources . . . . . . . . 561
13.5.4 Other Current Sources . . . . . . . . . . . 563
13.5.5 Wires and Cables . . . . . . . . . . . . . . . 564
13.6 Potential to Environment . . . . . . . . . . . . . . . . 565
13.7 Current Requirement Tests . . . . . . . . . . . . . . 566
13.7.1 Tests for a Coated System . . . . . . . . 567
13.7.2 Tests for a Bare Structure . . . . . . . . . 569
13.8 Stray Current Effects . . . . . . . . . . . . . . . . . . . . 569
13.9 Monitoring Pipeline Cathodic
Protection Systems . . . . . . . . . . . . . . . . . . . . . 571
13.9.1 Close Interval Potential Surveys . . . 571
13.9.2 Pearson Survey . . . . . . . . . . . . . . . . . 573
13.9.3 Direct and Alternating Current
Voltage Gradient Surveys . . . . . . . . 576
13.9.4 Corrosion Coupons . . . . . . . . . . . . . 577
13.10 Simulation and Optimization
of Cathodic Protection Designs . . . . . . . . . . . 578
13.10.1 Modeling Ship Impressed
Current Cathodic Protection . . . . . . 579
13.10.2 Modeling Cathodic Protection
in the Presence of Interference . . . . 582
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 585
14 Protective Coatings . . . . . . . . . . . . . . . . . . . . . . . . . . . 587
14.1 Types of Coatings . . . . . . . . . . . . . . . . . . . . . . 587
14.2 Why Coatings Fail . . . . . . . . . . . . . . . . . . . . . . 588
14.3 Soluble Salts and Coating Failures . . . . . . . . 592
14.4 Economic Aspects of Coatings
Selection and Maintenance . . . . . . . . . . . . . . 598
14.5 Organic Coatings . . . . . . . . . . . . . . . . . . . . . . . 603
14.5.1 Coating Functionality . . . . . . . . . . . 603
14.5.2 Basic Components . . . . . . . . . . . . . . 610