Corrosion and its preventive measures
- 1. Corrosion Prevention Presented by N.Nagadatt Sharma Submitted to Dr. P. Venkateshwara Rao
- 2. Contents: 1. What is corrosion? 2. Basic Principles of Corrosion Control 3. Causes of corrosion 4. Types of Corrosion 5. Corrosion Prevention methods 6. Corrosion detection and measurement. 7. Corrosion Inhibitors. 8. Conclusion 9. References
- 3. What is corrosion? Corrosion is natural phenomenon which attacks metal by chemical, electrochemical action converts metal into metallic compound , such as an oxide , hydroxide or sulphate. Destruction or deterioration and consequent loss of solid metallic materials , starting at its surface dueto chemical or electro chemical attack, by their environment. Corrosion is major problem worldwide in all industrial sectors. It impacts on safety , health and environmental issues .
- 4. Basic principles of corrosion Corrosion cycle
- 6. Causes of Corrosion Pure or noble metals such as gold, silver, platinum, aluminum , copper do not corrode since they are chemically uncombined in their naturalstate. Following conditions must exist beforecorrosion. i) Presence of metal that will corrode (anode) ii) Presence of cathode iii)Presence of conductive liquid(electrolyte) iv)Electrical contact between anode and cathode Elimination of any one of these condition will reduce or stop corrosion.
- 7. Classification of Corrosion on the basis of working temperature i) Low temperature Corrosion ii) High temperature Corrosion on the basis of working environments i) Dry or Chemical Corrosion ii) Wet or Electrochemical Corrosion
- 8. Dry or Chemical Corrosion It occurs when oxygen in air reacts with metal , without presence of liquid. It is very sensitive totemperature Rate of dry corrosion varies from metal to metal , as a result of mechanisms involved. Oxide layer on steel & iron is known as rust. In aluminum , copper oxide layer formed due to reaction with atmospheric oxygen ,stops further corrosion. As oxide layer formed , prevents further contact of oxygen as film is non porous. • This stopping is known as Passivations. • Active Corrosion-steel, CI , Mg.
- 9. Wet or Electrochemical Corrosion It is electrochemical phenomenon , whichoccurs in galvanic cell. Particularly when two metals are in contact with a liquid , liquid containing salt and electric potential is formed between the metals. in some cases in single metal , when comes in contact with liquid or electrolyte , a anodeand cathode areas are created. When anode area starts corroding with respect to cathode areas , is termed as wet corrosion. Electrochemical reaction – transfer of electrons Electrochemical corrosion cell- Electrical circuit and its associated chemical reaction are called electrochemical corrosion cell.
- 10. Dry or Chemical Corrosion Wet or Electrochemical Corrosion
- 11. Anodic & cathodic reactions in corrosion cell At Anode-Oxidation Fe Fe 2e2 At Cathode -reduction O 2H O 4e 4OH 2 2
- 12. Factors InfluencingCorrosion Type of Metal Heat treatment & Grain direction Presence of dissimilar metal Anode & cathode surface area Temperature presence of electrolyte Availability of oxygen time of exposure to corrosive environment
- 13. Types of corrosion Pitting Corrosion- Aluminum, Mg alloys, Cu alloy Factors influencing pitting Corrosion Alloying elements Surface finish Heat treatment
- 14. Types of corrosion • Stress corrosion: It is combined action of corrosive environment and mechanical stresses which often due to poor design or poor maintenance practice. • Stress corrosion cracking (SCC) is intergranular cracking of metal caused by stress& corrosion.
- 15. Types of corrosion Cavitation Corrosion Protective films are removed from metal surface during fluid flow. Low pressure development due to discontinuity in flow path , causes vapor bubbles to form in fluid steam. Due to collapsing of bubbles shock waves produced and removes protective film from metal surface
- 16. Types of corrosion Hydrogen Embrittlement Hydrogen blisters results from hydrogen atoms , formed during sulfide corrosion process on steel. Hydrogen atom combines to form hydrogen molecule Hydrogen blisters on steelsurface 3Fe 4 H 2 O Fe3O4 4 H 2
- 17. Types of corrosion Inter Granular Corrosion Form of corrosion where boundaries of grain of metal are more susceptible to corrosion than inside grain. Difference in Corrosion potential between grain and grain boundary. e.g. CuAl2 in Al alloys, Cr23C6 in stainlesssteel Formation of chromium carbide precipitants (Cr23C6) at grain boundary occurs when stainless steel of type 300 are heated to a temperature of 400 to 9000 C in rolling mill or fabrication or welding.
- 18. Types of corrosion Crevice Corrosion: • Localized attack that occurs in restricted areas , gaskets, flanges, fasteners, lap joints. • Occurs between two metal plassets.
- 19. Types of corrosion • Erosion corrosion • It results from loss of film under high velocity or high turbulent fluid flow. • Corrosion reaction which is accelerated by relative movement between corrosive fluid and metal surface. • High Turbulence intensity • impact velocity , angle, relative density between particle and fluid, particle size.
- 20. Types of corrosion GalvanicCorrosion • It occurs when two metals , with different compositions are connected in presence of electrolyte. • Current will flow from anode tocathode. • Rate of galvanic corrosion depends on difference in electrolytic potentials.
- 21. Control or Prevention of SCC 1. Control of stress level and Hardness. 2. Avoid chemical corrosion that causes SSC 3. Control of temperature 4. Modification in design , that will reduce SCC
- 22. Control of cavitation Corrosion- 1. Careful material selection i.e. high alloy steels containing Ni, Cr, W 2. Use of soft rubber coating , it absorbs cavitation energy 3. Smooth Surface finish
- 23. Prevention of Intergranular Corrosion Use of low grade stainless steel (304 L, 316L grades) due to which less carbon will be available for precipitation of chromium carbide. Use of stabilized grade of stainless steel (321, 322 grade) titanium Use of post weld treatment. Use of low grade stainless steel (304 L, 316L grades) due to which less carbon will be available for precipitation of chromium carbide. Use of stabilized grade of stainless steel (321, 322 grade) titanium
- 24. Prevention of crevice corrosion • Avoid crevice during fabrication i.e. smooth weld. • avoid solution get into crevice i.e. apply grease to nuts and bolts. • routine cleaning • Apply external coating.
- 25. control of erosion corrosion • selection of resistant materials- high wear resistance , high hardness • Decreasing flow velocity • minimizing the turbulence
- 26. control of Galvanic corrosion • selection of metals that are close together in galvanic series. • Insulate metal from each other • Painting of both metals
- 27. Other Corrosion Prevention methods Active corrosion protection : Toinfluence reactions which proceed during corrosion. e.g. Addition of inhibitors to aggressive medium. Passive corrosion protection :y mechanically isolating package contents from aggressive corrosive agents by using protective layers , films, coatings. This method neither changes ability of package contents to corrode nor aggressiveness of corrosive agent. Permanent corrosion protection Toprovide protection at the place of use. e.g. stable oxide layer (nonporous film)forming metals Temporary Corrosion protection Stresses occurring during transport, handling, storage are much greater than those occuring at place of use. e.g. extreme variation in temperature which results in condensation during transportation.
- 28. Corrosion Inhibitors • Chemicals that react with metallic surface & gives certain level of protection. • inhibitors has chemical bonding with base metal , it is more adherent to base metal , due to which corrosion reaction stopped.
- 29. Other protection methods Cathodic Protection Sacrificial Anode method
- 30. Other protection methods Use of coatings Electroplating Metal Spraying Hot Dippping
- 31. Measurement of Corrosion 1. Weight Loss Method- MPY=22300 𝑊 𝐴 𝐴 𝐴 2. Electrical Resistance Method- Electrical Resistance increases as corrosion decreases the cross-section of metallic material