Electrocorrosion and Protection of Metals
General approach with particular consideration to electrochemical plantsBy
- Joseph Riskin, M.Sc. in Chemical Engineering, Ph.D. in Corrosion and Protection of Metals, Consulting (corrosion protection of metals, failure analysis)
Electrocorrosion, the corrosion of metallic constructions by external currents, is the most significant factor in conductive aggressive environments. Corrosion of underground and underwater metal constructions by stray currents has been comprehensively studied in the past decades and is considered here only in the form of a review. The primary attention is on corrosion, by external anodic (mainly) and cathodic currents, of metal constructions in the highly aggressive environments typical for electrochemical plants, where penetration of the external currents (leakage currents) from the electrolytic baths into metal constructions is unavoidable.
A new approach to the problem of electrocorrosion protection of passive structural metals is considered in this book, keeping the metals attacked by external currents in the boundaries of their passive field. The systems, developed in accordance with this approach, are based on the modification of existing and elaboration of new methods of electrocorrosion protection. These systems take into account corrosion and electrochemical characteristics of the aggressive media (redox potential, conductivity etc.) and of the passive metal (corrosion and activation potentials, current density in a passive state, etc) as well as the sizes and distribution character of the external currents.
The book covers analysis of leakage current distributions in electrochemical plants, their influence, methods to estimate corrosion stability of metallic structures subject to external currents and presents many concrete examples of the successful introduction of corrosion protection systems in operating plants.
University and Industrial Libraries with Research Centers on Corrosion and Materials Science. Chemical, Petrochemical Industries.Metallurgists.
Hardbound, 264 Pages
Published: November 2008
"This volume is essential for chemical engineers and chemists that design, construct and operate electrochemical plants. Also, maintenance personnel, including materials and mechanical engineers, will benefit from reading, using and owning this compendium, in their daily endeavors. University lecturers and researchers will use it for undergraduate and postgraduate students preparing their theses on industrial corrosion. Electrochemical industry directors and executives should distribute it to the managers and engineers of their plants, to apply it in monitoring and controlling electrocorrosion. We hope that the book will encourage the corrosion community to employ the concepts and the methods that the author has so convincingly presented, to combat electrocorrosion."--Corrosion Engineering, Science and Technology 2010 VOL 45 NO 4 249"Throughout the book, each chapter is packed with learned references but mainly from the past experience of the author in the Soviet Union without modern up-to-date references from the electrochemical industry in other advanced countries. This volume is essential for chemical engineers and chemists that design, construct and operate electrochemical plants. Also, maintenance personnel, including materials and mechanical engineers, will benefit from reading, using and owning this compendium, in their daily endeavors. University lecturers and researchers will use it for undergraduate and postgraduate students preparing their theses on industrial corrosion. Electrochemical industry directors and executives should distribute it to the managers and engineers of their plants, to apply it in monitoring and controlling electrocorrosion. We hope that the book will encourage the corrosion community to employ the concepts and the methods that the author has so convincingly presented, to combat electrocorrosion"--Corrosion Engineering, Science & Technology Journal
Introduction: Corrosion and electric current 200 years together.
1. Dependence of the corrosion behavior of metals attacked by an external current on their initial state.
1.1. State of metals in aggressive media in the absence of attack by external currents
1.2. Polarization of metals
1.3. Attack of external anodic current on actively corroding metals
1.4. Attack of external anodic current on passive metals
1.5. Attack of external anodic current on thermodynamically stable metals
1.6. Attack of external cathodic current on metals
1.7. Attack of external alternating current on metals
1.8. External current as a factor of the aggressiveness of the environment
2. Corrosion and protection of underground and underwater structures attacked by stray currents.
2.1. Main media, sources of stray currents and objects of their corrosive attack
2.2. Methods of detection and control of stray currents
2.3. Metal corrosion by stray currents
2.4. Protection of metals against corrosion attack by stray currents
2.4.1. Measures for reducing stray currents
2.4.2. Protection of underground structures by electrodrainage
2.4.3. Cathodic protection
3. Operating features of electrochemical plants.
3.1. General characteristics of electrochemical plants
3.2. Leakages currents in electrochemical plants
3.2.1. Sources of leakage currents, concepts and problems connected with them
3.2.2. Methods of measuring and controlling of leakage currents
3.2.3. Magnitudes and distribution regularity of leakage currents along the lines of Electrochemical cells
3.3. Aggressive media
4. Using structural metallic materials in electrochemical plants without taking into account attack by leakage currents.
4.1. Non-metallic materials
4.2. Traditional metallic materials
4.3. Experience in the field of titanium application
4.3.1. Preconditions for the application of titanium in electrochemical plants
4.3.2. Attempts at titanium application in the zones of attack by leakage currents
4.3.3. Preconditions and experience of titanium application in wet chlorine lines of electrochemical plants
4.3.4. Laboratory and industrial tests of titanium resistance against crevice corrosion in wet chlorine and in chlorine-saturated water. Comparison of results.
5. Corrosion behavior investigations of traditional structural metallic materials in electrochemical plant media, taking into account attack by leakage currents.
5.1. Carbon steel in neutral, alkaline and chloride-alkali media
5.1.1. Neutral solutions of salts
5.1.2. Alkaline solutions
5.1.3. Chloride-alkali solutions
5.2. Stainless steel 18-10 in alkaline and acid media
5.2.1. 50% naoh solution at 120oc; comparison of corrosion behavior of SS18-10 and of Nickel
5.2.2. Technological solution for producing sodium perborate
5.2.3. Acid sulfate containing electrolyte for copper electrorefining
6. Corrosion behavior investigations of titanium and its alloys in the media of electrochemical plants, taking into account the attack by anodic leakage currents.
6.1. Corrosion and electrochemical characteristics of titanium
6.2. Chloride and chloride-alkali media of chlorine-producing electrochemical plants
6.3. Electrolyte of copper electrorefining
6.4. Media of nickel electrorefining
6.5. Influence of welding seams and crevices
6.5.1. Welding seams
6.5.2. Artificial crevices
6.6. Titanium alloys
7. Hydrogenation and corrosion investigations of titanium under attack by an external cathodic current.
7.1. Conditions of hydrogenation and corrosion of titanium. Methodological features of experiments
7.2. Investigations in non-stirred nacl solutions
7.3. Investigations under conditions of electrolyte stirring and flowing
7.3.1. Relation between the corrosion rate of titanium and the accumulation of Oxygen-chlorine compounds in the solution
7.3.2. Two corrosion mechanisms of hydrogenated titanium
7.4. Welding seams
7.5. Hydrogenation of cathode matrixes in solution of nickel electrorefining
7.5.1. Electrochemical investigations of combined discharge of nickel and hydrogen ions on titanium
7.5.2. Radiochemical investigations of titanium hydrogenation in the process of nickel deposition
8. Estimation of corrosion stability of structures made of passive metals in aggressive media, in the field of an external current.
8.1. Estimation based on the potential value
8.1.1. Activation potential as an estimation criterion of the passive metal state in the field of an external current
8.1.2. Types of structural elements in the form of tubes in the field of an external current
8.1.3.Potential and current distribution along structural elements in the form of tubes
8.1.4. Computation procedure of potential distribution along the internal tube surface with the help of a computer
8.2. Estimation based on the external current value
8.3. Practical steps and examples of corrosion stability estimation of structures in the form of tubes of different types
8.4. Significance of the electrochemical characteristics of passive metals for the estimation and provision of the corrosion stability of metallic structures
9. Electrocorrosion protection of metals in electrochemical plants based on existing methods.
9.1. Insulating coatings
9.2. Reduction of leakage currents coming from electrochemical cells
9.2.1. Reduction of leakage currents along electrolyte piping and prevention of current oscillations
9.2.2. Reduction of leakage currents along piping of wet gases
9.3. Sectionalization of piping made of passive metals
9.4. Possibilities of applying traditional methods of electrochemical protection and their modifications for electrochemical plants
9.4.1. Electrodrainage protection
9.4.2. Protection by sacrificial anodes for current drainage in chloride electrolysis plants
9.4.3. Protection by sacrificial anodes for current drainage in electrolysis plants with metal deposition
10. New principles of protection of passive metals against electrocorrosion in electrochemical plants.
10.1. Protection of metals with the relationship ∆ = (Eox Ea) < 0, against corrosion attack by an external anodic current, with the help of dimensionally stable anodes current leak-offs
10.1.1. Theoretical basis
10.1.2. Experimental verification of the protection principle
10.2. Corrosion protection with the help of dimensionally stable anodes, oriented along the field of the external current
10.2.1. Theoretical basis
10.2.2. Investigation of the protection principle
10.3. Protection of metals against corrosion attack by an external cathodic current
10.4. Protection of metals against corrosion attack by leakage currents which periodically change their direction
10.5. Protection of metals against corrosion attack by external currents at the stage of design
11. Electrodes for metal protection against corrosion attack by external currents in electrochemical plants.
11.1. Requirements upon materials of electrodes that are used for protection against corrosion attack by external currents
11.2. Application of dimensionally stable anodes of commercial electrolysis processes for protection against electrocorrosion
11.2.1. Neutral and acid chloride-containing media
11.2.2. Chloride-sulfate media
11.3. Anodes for media containing sulfuric acid
11.4. Dimensionally stable anodes with a coating obtained on the basis of intermetallic compounds produced in electric spark
11.4.1. Preconditions for the choice of materials and methods of producing the anodes. Test conditions
11.4.2. Investigations in chloride solutions
11.4.3. Investigations in chloride-alkali solutions
11.5. Stable cathodes
11.5.1. Cathodes for media containing dissolved chlorine and for chloride media
11.5.2. Titanium cathodes for other aggressive media
11.5.3. Possibilities of increasing the stability of titanium cathode blanks
12. Industrial tests and the introduction into electrochemical plants of developed methods for the protection of metals against corrosion attack by leakage currents.
12.1. Protection by sacrificial anodes in electrorefining plants
12.1.1. Industrial tests
12.1.2. Introduction of protection
12.2. Industrial tests and the introduction of corrosion protection of titanium structures by anodes current leak-offs
12.2.1. Industrial tests
12.2.2. Introduction of protection
12.3. Industrial tests and the introduction of corrosion protection by anodes, oriented along the field of the external current in electrochemical plants
12.3.1. Industrial tests
12.3.2. Introduction of protection
12.4. Industrial tests of titanium protection against corrosion attack by cathodic leakage currents with the help of stable cathodes
12.5. Combined protection of metals against corrosion attack by leakage currents
12.6. Effectiveness and possibilities of using the developed methods of metal protection against electrocorrosion