PHARMACEUTICAL ENGINEERING

UNIT 5

1. UNIT -5 CORROSION TYPES AND ITS PREVENTION 26/09/2020 1

2. TYPES OF CORROSION 2

3. It is also known as uniform attack corrosion . It is the most common type of corrosion and is caused by a chemical or electrochemical reaction that damages the entire exposed surface of a metal. 3 A.GENERAL CORROSION

4. Intergranular corrosion: It is a corrosion of a chemical or electrochemical attack on the grain boundaries of metal. It often occurs due to impurities in the metal which tends to be present in higher content near the grain boundaries. 4 B.LOCALISED CORROSION

5. 2.Pitting corrosion Pitting corrosion occurs when a small hole or cavity is formed in the metal, usually as a result of de- passivation of a small area. This area becomes anodic, while a part of the remaining metal becomes cathodic, producing a localized galvanic reaction. This form of corrosion is often difficult to detect because it is generally relatively small and can be covered and hidden by compounds produced by corrosion. 5

6. 3. Crevice corrosion: Crevice corrosion: Similar to pitting, crevice corrosion occurs at a specific location or crevices. The solution get deposited to crevices and drying of liquid takes more time. As a result crevice corrosion occurs. This type of corrosion is often associated with a stagnant micro-environment. Acidic conditions or a depletion of oxygen in a crevice can cause crevice corrosion. 6

7. 4. Stress corrosion When tensile stress is greater than yield stress, then cracks develop on the surface. For example: cold formed brass develop cracks in presence of ammonia environment. 7

8. 5. Fretting Corrosion Fretting corrosion occurs as a result of repeated wearing or due to sliding or vibration of metals on an uneven rough surface. The corrosion occur due to generation of frictional heat which produce oxide films which continuously removed and cause corrosion at fresh surface. This can be avoided by minimizing friction or by proper lubrication of equipment. 8

9. 6. Erosion Corrosion This occur due to destruction of metal by combination of abrasion and attrition caused by flow of liquid or gas. The factors, such as alloy content of steel, pipe system design, component geometry and water composition, influence erosion.  9

10. 7. Cavitation Corrosion Cavitation erosion occurs due to formation of vacuum bubbles in liquid stream when passed over the surface. The bubbles on metal surface get collapsed and cause damage and further corrosion. This type of corrosion generally occur around propellers. This can be avoided by using more resistant metal and by using protective coating. 10

11. 8. Galvanic Corrosion Galvanic corrosion occurs when two different metals are found together in a corrosive electrolyte. A galvanic cell is formed between the two metals, where one metal becomes the anode and the other the cathode. The anode corrodes and deteriorates faster while the cathode deteciorates more slowly. Protective oxide film reduce galvanic corrosion. 11

12. 9. Oxygen concentration cell Oxygen concentration cell: This type of corrosion occur due to difference in amount of oxygen in solution at one point when compared with other. The least oxygen concentration increase rate of corrosion. Redesign of equipment avoid such type of corrosion. 12

13. 10. Corrosion fatigue Due to repetition metal surface get corroded by corrosive media. The protective oxide film that prevent corrosion get ruptured at higher rate as compared to new protective film. Therefore ,surface loose its fatigue resistance and finally equipment get deteriorate. 13

14. 11. Impingement attack or corrosion It is also called velocity accelerated corrosion. This type of corrosion is accelerated by removal of oxide films. 14

15. 12. Hydrogen Embrittlement Penetration of hydrogen into metals cause loss in ductility. At elevated temperature, cracking of carbon steel occur. As a result, failure occur by embrittlement , cracking and blistering. The solution of hydrogen sulphide and hydrocyanic acid is susceptible to this form of attack. 15

16.   C. STRUCTURAL CORROSION In this type of corrosion, structural strength of metal get reduced due to corrosion. It is of two type a. Graphite corrosion : Graphite corrosion generally involve Gray Cast iron in which metallic iron get converted into corrosion product. This produce residue of intact graphite which is mixed with iron corrosive product and insoluble components of cast iron. b. Dezincification: This is observed in brass which contain 15% zinc. The major constituent of corrosion is metallic copper. The mechanism behind corrosion is (1) Redeposition of copper over corrosion products (2) Formation of zinc corrosion products leaving copper residue. This type of corrosion can be decreased by adding little amount of arsenic, antimony, phosphorus to the alloy 16

17.  D. BIOLOGICAL CORROSION Corrosion occur due to metabolic activity of microorganism which cause deterioration of metal . The biological corrosion is due to: a. Changing resistance to surface film b. Developing electrolyte-concentration cells on metal surface c. Developing corrosive environment d. Altering rate of anodic/cathodic reaction. 17

18. PREVENTION OF CORROSION 18

19. 19 PREVENTION OF CORROSION

20. 20 PREVENTION OF CORROSION

21. THANK YOU 21