Types of corrosion and Prevention of corrosion

Types of corrosion, their features and
Prevention of corrosion

1. 1 Types of corrosion, their features and Preventive measures

2. Corrosion Corrosion is a natural process. It is defined as the natural process that causes the transformation of pure metals to undesirable substances when they react with substances like water or air. This reaction causes damage and disintegration of the metal starting from the portion of the metal exposed to the environment and spreading to the entire bulk of the metal. 2

3. Types of Corrosion 3

4. 1. Atmospheric Corrosion Atmospheric corrosion is a type of wet corrosion caused by the action of electrolytes. In this case, moisture present in the atmosphere, rainwater, etc. acts as electrolytes triggering corrosion of the exposed metal surface. 4

5. 2. Erosion Corrosion Erosion corrosion is caused by mechanical abrasion due to the relative movement between metal surfaces and corrosive fluids. In this case, the surface of metal gets deteriorated gradually by the abrasion of fast-moving fluids and cavities are also formed. This type of corrosion commonly seen in metal tubes carrying moving fluids in it. 5

6. 3. Selective Corrosion Selective corrosion occurs in alloys where one of the component metals is de-alloyed by the corrosive environment. This type of corrosion can be seen in brass alloy pipes where zinc is commonly used as another component and here zinc is de-alloyed. Similarly in the case of copper nickel alloy tubes where nickel is de-alloyed by selective corrosion. 6

7. 4. Uniform Corrosion In case of uniform corrosion, a uniform layer of rust is formed on the surface of metals and it is extended over the whole surface area of metal. This type of corrosion can be seen in metals which are not protected by surface coating. Aluminum, zinc, lead, etc. are some metals commonly affected by uniform corrosion. 7

8. 5. Pitting Corrosion Pitting is the formation of rust pits or holes on the surface. Pitting corrosion is a localized form of corrosion where the corrosion is limited to small areas. The shapes of rust pits may not be similar but in most of the cases, they are hemispherical in shape. 8

9. 6. Fretting Corrosion Fretting corrosion occurs at the contact area of the two materials which are joined together. This is developed when the contact area is subjected to slips and vibrations. This type of corrosion can be seen in bolted and riveted joints, clamped surface, etc. 9

10. 7. Stress Corrosion Stress corrosion caused by the combined action of a corrosive environment and mechanical stress on the surface of the material. In its initial stage, small cracks are developed and these finally leads to failure of the whole structure. This type of corrosion can be seen in stainless steel when they are stressed in chloride environments, in brass materials when they are stressed in the presence of ammonia, etc. 10

11. 8. Inter-granular Corrosion Inter-granular corrosion is the corrosion occurs along the grain boundaries and the grains are not affected in this case. It is caused when there is a noticeable difference in reactivity against impurities exists between grain boundaries and grains. This difference in reactivity occurs due to defective welding, heat treatment stainless steels, copper, etc. 11

12. 9. Corrosion Fatigue Fatigue of materials is defined as the failure of a material due to repeated application of stress. When the fatigue of metal is developed in the corrosive environment then it called corrosion fatigue. This can be prevented by improving the fatigue resistance of a material. 12

13. Prevention of Corrosion 13

14. Material Selection - Galvanic Series Magnesium Zinc Aluminium Mild Steel Cast Iron Copper Stainless Steel Gold Platinum 14

15. Design of Structures Avoid sharp corners Complete draining of vessels No water retention Avoid sudden changes in section Avoid contact between dissimilar metals Easy replacement of vulnerable parts Avoid excessive mechanical stress Weld rather than rivet 15

16. Inhibitors Inhibitors are materials that may be injected into the system . They plate out on the surface and inhibit the formation of corrosion cells. They are commonly used in pipelines and other vessels that will contain materials that are corrosive. 16

17. Cathodic Protection Cathodic protection is a technique to control the corrosion of a metal surface by making it work as a cathode of an electrochemical cell. In this process, the base metal is connected to a sacrificial metal that corrodes instead of the base metal. By doing so this sacrificial metal (which is more reactive than the base metal) will give out electrons and get oxidized. The ions thus formed takes part in the corrosion reactions thereby saving the base metal. Cathodic protection systems are most commonly used to protect steel, water or fuel pipelines and storage tanks, steel pier piles, ships. 17

18. Galvanization This process involves coating iron with a thin layer of zinc. It is generally done by dipping iron in molten zinc. The zinc layer coating thus protect the iron inside from corrosion. A common example of galvanic corrosion occurs in  galvanized iron , a sheet of iron or steel covered with a zinc coating. Even when the protective zinc coating is broken, the underlying  steel is not attacked. A spectacular example of galvanic corrosion occurred in the  Statue of Liberty . 18

19. Protective Coatings Most popular method of corrosion protection Coatings are of various types: Metallic Inorganic like glass, porcelain and concrete Organic, paints, varnishes and lacquers 19

20. Reference https://theconstructor.org/ https://byjus.com/ https://www.slideshare.net/ https://industrytoday.com/ 20

21. Thank You 21