Prevention of corrosion


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A presentation covering the various methods of prevention of corrosion. Material selection, design of structures, alteration of materials, alteration of environment, cathodic & anodic protection, and coatings are the different methods used. These are briefly described.

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Prevention of corrosion

  1. 1. PREVENTION OF CORROSION Dr. T. K. G. Namboodhiri [Retd. Professor., Inst. Techno. , Banaras Hindu University] Consultant-Metallurgy & Corrosion, Tiruvalla, Kerala
  2. 2. PREVENTION OF CORROSION <ul><li>The huge annual loss due to corrosion is a national waste and should be minimized </li></ul><ul><li>Materials already exist which, if properly used, can eliminate 80 % of corrosion loss </li></ul><ul><li>Proper understanding of the basics of corrosion and incorporation in the initial design of metallic structures is essential </li></ul>
  3. 3. METHODS <ul><li>Material selection </li></ul><ul><li>Improvements in material </li></ul><ul><li>Design of structures </li></ul><ul><li>Alteration of environment </li></ul><ul><li>Cathodic & Anodic protection </li></ul><ul><li>Coatings </li></ul>
  4. 4. MATERIAL SELECTION <ul><li>Most important method – select the appropriate metal or alloy . </li></ul><ul><li>“ Natural” metal-corrosive combinations like </li></ul><ul><li>S. S.- Nitric acid, </li></ul><ul><li>Ni & Ni alloys- Caustic </li></ul><ul><li>Monel- HF, Hastelloys- Hot HCl </li></ul><ul><li>Pb- Dil. Sulphuric acid, </li></ul><ul><li>Sn- Distilled water </li></ul><ul><li>Al- Atmosphere, </li></ul><ul><li>Ti- hot oxidizers </li></ul><ul><li>Ta- Ultimate resistance </li></ul><ul><li>Corrosion Tables available for various materials in different corrosive environments </li></ul>
  5. 5. IMPROVEMENTS OF MATERIALS <ul><li>Purification of metals- Al , Zr </li></ul><ul><li>Alloying with metals for: </li></ul><ul><li>Making more noble, e.g. Pt in Ti </li></ul><ul><li>Passivating, e.g. Cr in steel </li></ul><ul><li>Inhibiting, e.g. As & Sb in brass </li></ul><ul><li>Scavenging, e.g. Ti & Nb in S.S </li></ul><ul><li>Improving other properties </li></ul><ul><li>Change of microstructure. e.g. desensitization of s. s. welds.- prevents I.g. corrosion </li></ul><ul><li>Elimination of tensile stress-improves SCC </li></ul><ul><li>Introduction of surface compressive stress-improves corrosion fatigue and SCC. </li></ul>
  6. 6. DESIGN OF STRUCTURES <ul><li>Avoid sharp corners </li></ul><ul><li>Complete draining of vessels </li></ul><ul><li>No water retention </li></ul><ul><li>Avoid sudden changes in section </li></ul><ul><li>Avoid contact between dissimilar metals </li></ul><ul><li>Weld rather than rivet </li></ul><ul><li>Easy replacement of vulnerable parts </li></ul><ul><li>Avoid excessive mechanical stress </li></ul>
  7. 7. ALTERATION OF ENVIRONMENT <ul><li>Lower temperature and velocity </li></ul><ul><li>Remove oxygen/oxidizers </li></ul><ul><li>Change concentration </li></ul><ul><li>Add Inhibitors </li></ul><ul><ul><li>Adsorption type, e.g. Organic amines, azoles </li></ul></ul><ul><ul><li>H evolution poisons, e.g. As & Sb </li></ul></ul><ul><ul><li>Scavengers, e.g. Sodium sulfite & hydrazine </li></ul></ul><ul><ul><li>Oxidizers, e.g. Chromates, nitrates, ferric salts </li></ul></ul>
  8. 8. CATHODIC & ANODIC PROTECTION <ul><li>Cathodic protection: Make the structure more cathodic by </li></ul><ul><ul><li>Use of sacrificial anodes </li></ul></ul><ul><ul><li>Impressed currents </li></ul></ul><ul><li>Used extensively to protect marine structures, underground pipelines, water heaters and reinforcement bars in concrete </li></ul><ul><li>Anodic protection: Make Passivating metal structures more anodic by impressed potential. e.g. 316 s.s. pipe in sulfuric acid plants </li></ul>
  9. 9. COATINGS <ul><li>Most popular method of corrosion protection </li></ul><ul><li>Coatings are of various types: </li></ul><ul><ul><li>Metallic </li></ul></ul><ul><ul><li>Inorganic like glass, porcelain and concrete </li></ul></ul><ul><ul><li>Organic, paints, varnishes and lacquers </li></ul></ul><ul><li>Many methods of coating: </li></ul><ul><ul><li>Electrodeposition </li></ul></ul><ul><ul><li>Flame spraying </li></ul></ul><ul><ul><li>Cladding </li></ul></ul><ul><ul><li>Hot dipping </li></ul></ul><ul><ul><li>Diffusion </li></ul></ul><ul><ul><li>Vapour deposition </li></ul></ul><ul><ul><li>Ion implantation </li></ul></ul><ul><ul><li>Laser glazing </li></ul></ul>
  10. 10. CONCLUSIONS <ul><li>Many methods are available to prevent/mitigate corrosion </li></ul><ul><li>One or a number of methods may be used simultaneously for effective protection </li></ul><ul><li>Proper selection of methods is essential for optimizing cost. </li></ul>