Electrocorrosion and Protection of Metals

Preface.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 metals1.3. Attack of external anodic current on actively corroding metals1.4. Attack of external anodic current on passive metals1.5. Attack of external anodic current on thermodynamically stable metals1.6. Attack of external cathodic current on metals1.7. Attack of external alternating current on metals1.8. External current as a factor of the aggressiveness of the environment2. 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 attack2.2. Methods of detection and control of stray currents2.3. Metal corrosion by stray currents2.4. Protection of metals against corrosion attack by stray currents2.4.1. Measures for reducing stray currents2.4.2. Protection of underground structures by electrodrainage2.4.3. Cathodic protection3. Operating features of electrochemical plants. 3.1. General characteristics of electrochemical plants3.2. Leakages currents in electrochemical plants3.2.1. Sources of leakage currents, concepts and problems connected with them3.2.2. Methods of measuring and controlling of leakage currents3.2.3. Magnitudes and distribution regularity of leakage currents along the lines of Electrochemical cells 3.3. Aggressive media4. Using structural metallic materials in electrochemical plants without taking into account attack by leakage currents. 4.1. Non-metallic materials 4.2. Traditional metallic materials4.3. Experience in the field of titanium application4.3.1. Preconditions for the application of titanium in electrochemical plants4.3.2. 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 plants4.3.4. 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 media5.1.1. Neutral solutions of salts5.1.2. Alkaline solutions5.1.3. Chloride-alkali solutions 5.2. Stainless steel 18-10 in alkaline and acid media5.2.1. 50% naoh solution at 120oc; comparison of corrosion behavior of SS18-10 and of Nickel5.2.2. Technological solution for producing sodium perborate5.2.3. Acid sulfate containing electrolyte for copper electrorefining6. 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 titanium6.2. Chloride and chloride-alkali media of chlorine-producing electrochemical plants6.3. Electrolyte of copper electrorefining6.4. Media of nickel electrorefining6.5. Influence of welding seams and crevices6.5.1. Welding seams6.5.2. Artificial crevices6.6. Titanium alloys7. 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 experiments7.2. Investigations in non-stirred nacl solutions7.3. Investigations under conditions of electrolyte stirring and flowing7.3.1. 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 titanium7.4. Welding seams7.5. Hydrogenation of cathode matrixes in solution of nickel electrorefining7.5.1. Electrochemical investigations of combined discharge of nickel and hydrogen ions on titanium7.5.2. Radiochemical investigations of titanium hydrogenation in the process of nickel deposition8. 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 value8.1.1. Activation potential as an estimation criterion of the passive metal state in the field of an external current8.1.2. Types of structural elements in the form of tubes in the field of an external current8.1.3.Potential and current distribution along structural elements in the form of tubes8.1.4. Computation procedure of potential distribution along the internal tube surface with the help of a computer8.2. 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 structures9. Electrocorrosion protection of metals in electrochemical plants based on existing methods. 9.1. Insulating coatings9.2. Reduction of leakage currents coming from electrochemical cells9.2.1. Reduction of leakage currents along electrolyte piping and prevention of current oscillations9.2.2. Reduction of leakage currents along piping of wet gases9.3. Sectionalization of piping made of passive metals 9.4. Possibilities of applying “traditional” methods of electrochemical protection and their modifications for electrochemical plants9.4.1. Electrodrainage protection9.4.2. Protection by sacrificial anodes for current drainage in chloride electrolysis plants9.4.3. Protection by sacrificial anodes for current drainage in electrolysis plants with metal deposition10. 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 basis10.1.2. Experimental verification of the protection principle10.2. Corrosion protection with the help of dimensionally stable anodes, oriented along the field of the external current 10.2.1. Theoretical basis10.2.2. Investigation of the protection principle10.3. Protection of metals against corrosion attack by an external cathodic current10.4. Protection of metals against corrosion attack by leakage currents which periodically change their direction10.5. Protection of metals against corrosion attack by external currents at the stage of design11. 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 currents11.2. Application of dimensionally stable anodes of commercial electrolysis processes for protection against electrocorrosion11.2.1. Neutral and acid chloride-containing media11.2.2. Chloride-sulfate media11.3. Anodes for media containing sulfuric acid11.4. Dimensionally stable anodes with a coating obtained on the basis of intermetallic compounds produced in electric spark11.4.1. Preconditions for the choice of materials and methods of producing the anodes. Test conditions11.4.2. Investigations in chloride solutions11.4.3. Investigations in chloride-alkali solutions11.5. Stable cathodes11.5.1. Cathodes for media containing dissolved chlorine and for chloride media11.5.2. Titanium cathodes for other aggressive media11.5.3. Possibilities of increasing the stability of titanium cathode blanks12. 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 plants12.1.1. 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-offs12.2.1. Industrial tests12.2.2. Introduction of protection12.3. Industrial tests and the introduction of corrosion protection by anodes, oriented along the field of the external current in electrochemical plants12.3.1. Industrial tests12.3.2. Introduction of protection12.4. Industrial tests of titanium protection against corrosion attack by cathodic leakage currents with the help of stable cathodes12.5. Combined protection of metals against corrosion attack by leakage currents12.6. Effectiveness and possibilities of using the developed methods of metal protection against electrocorrosionReferences.Index.