Corrosion control

A thorough insight into corrosion control, its types, causes, measures to control along with case studies.

1. Corrosion Control A Presentation by : PSV Narender Pranjal Ratan Saurabh Shakti Shikhar Sohan

2. Corrosion Fundamentals Corrosion can be defined as the degradation of a material due to reaction with its environment. Corrosion is Extractive Metallurgy in reverse. It is a spontaneous process. The driving force of corrosion is the tendency of the metals to have lower energy.

3. Why Corrosion Control? Economic Aspects : I t can be referred to as cost of corrosion under Direct Loss and Indirect Loss . Health Aspects : Surgical instruments, implants, pacemakers, etc. are all prone to corrosion . Cultural Aspects : Antiques and Monuments may get extinct due to corrosion. Safety Aspects : Machine parts in factories and home appliances can cause harm if corroded .

4. Prevention Measures Design Constraints Role of Materials Protective Coatings Cathodic Protection Environmental Modification Passivation

5. Design Constraints Design for proper drainage, less crevices, less stress, less water retention. Design for allowances.

6. Role of Materials Use of pure metals: eg: Aluminium, Titanium ,Gold, Platinum etc.... Use of corrosion resistant alloys. eg:Duralumin, Stainless steel, Brass, Bronze etc.... Fulfill required functionality in terms of strength and corrosion resistance.

7. Protective coatings Metal coating : Surface of a metal( base metal) is coated with another metal(coat metal). Painting: A suitable top coat which excludes water and oxygen from the surface. Polishing: Finely finishing the surface.

8. Metal Coating Hot Dipping : Base metal is dipped or passed through molten coat metal or alloy. Eg:Galvanization Metal Spraying : Coat metal is sprayed on base metal. Cementation : Base metal is protected by alloying its surface with another metal.

9. Metal Coating Metal Cladding: Base metal is sandwiched between thin layers of hot metal and pressed between rollers. Electroplating: Deposition of coat metal over base metal using electricity. Anodising: Formation of hydrated oxide layer of coat metal over base metal.

10. Painting Oil Painting: Most widely used consist of pigments and thinners. Water Painting: A suspension of dispersible pigments in emulsion of water and small quantities of drying oils. Special Paints: Special chemicals are added in paints specific purpose. Eg: Heat resistant paints, water repellant paints, etc.

11. Cathodic Protection The metal to be protected is connected to an external anode and a D.C. current is passed so that all areas of the metal surface become cathodic and do not corrode. Cathodic protection can be achieved in two ways: 1. By Sacrificial Anodes. 2. By Impressed Current.

12. Sacrificial Anodes These anodes consist of the highly reactive metal like Mg. To protect pipes, rods of Mg buried near the pipes and connected to them by wires. Thus Galvanic cells with high E.M.F are setup with surface to be protected made cathodic. The cost of replacement of corroded anodic Mg is much less than replacing pipes.

13. Impressed Current Method The object to be protected is made cathode of an electrolytic cell by connecting it to negative terminal of a D.C source. This is done by rectifying an A.C line or using D.C source. The positive terminal is connected to scrap iron.

14. Environmental Modification Deaeration: Removal of dissolved oxygen. Eg: By adding chemicals like Sodium Sulphite. Dehumidification: Removal of moisture from air. Eg: By adding chemicals like Silica. Inhibitors: It is a chemical additive which reduce the rate of corrosion. Eg: Alkali, Amines, Orthophosphates, etc.

15. Passivation It is using a light coat of material such as a metal oxide to create a shell against corrosion. It can only occur in certain conditions and is used in micro-electronics to enhance silicon.

16. Case Study: Iron Pillar, Delhi The iron pillar of Delhi has not rusted from the last 16 centuries due to the following reasons : Purity of its iron. High Phosphorus content. Low Sulphur and Magnesium. Better forge welding. Drier and uncontaminated atmospheric condition.

17. Case Study: Eiffel Tower The structure comprises 220000 metre square of surface (300 tonnes of wrought iron) that have to be maintained and repainted every 7 years, consuming 50 tonnes of lead free paint. for r enovation ,corroded areas are prepared before painting. All this is carried out by around 25 painters, works lasting for around 15 months and costing over 20 million francs.

18. Conclusion Thus we understood the basics behind corrosion and its aspects in practical life. We also looked at various aspects of corrosion control along with 2 case studies. Thus this presentation underlines the importance of corrosion control and its significance for the model world.

19. Reference Textbook of engineering chemistry by:- R Gopalan, D Venkappayya, Sulochana Nagarajan. corrosion.ksc.nasa.org Lecture notes by Dr. K.G. Sreejalakshmi. Google. Wikipedia.