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Corrosión

Corrosión. Mr. JAYDEEP KHADE DY Patil College of Engineerig, Akurdi. INTRODUCTION. Corrosion can be defined as deterioration of metal(s) by chemical and/or electrochemical reaction with its environment [1]. Cost of corrosion. U.S. Cost of Corrosion = $460 Billion India = 2 lacks cr.

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Corrosión

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  1. Corrosión Mr. JAYDEEP KHADE DY Patil College of Engineerig, Akurdi

  2. INTRODUCTION Corrosion can be defined as deterioration of metal(s) by chemical and/or electrochemical reaction with its environment [1].

  3. Cost of corrosion • U.S. Cost of Corrosion = $460 Billion • India = 2 lacks cr

  4. DELHI IRON PILLER

  5. Reaction in corrosion • Anodic Reaction: The chemical reaction at the anode or metal dissolution can be written as • M = M n+ + ne- • In case of iron or steel, this equation becomes • Fe = Fe 2+ + 2e- • These electrons migrate to the cathode through the steel producing corrosion current. • Cathodic Reaction: The nature of the reaction at the cathode (in which the electrons released in anodic dissolution are consumed) depends upon the nature of the environment. • Oxygen reduction (Neutral or Basic solution): • O2 + 2H2O + 4e- = 4 (OH) –

  6. Mechansium of corrosion • Metals are thermodynamically unstable in their refined form and tend to revert their natural states through the process of corrosion. • Corrosion can be defined as the destruction or deterioration of a material because of reaction with its environment [1]. Electrochemical corrosion showing rusting of steel

  7. Electrochemical Corrosion Cell

  8. The Corrosion Puzzle

  9. Types of corrosion • Wet Corrosion: Is important in case of the many off –structures associated with oil and gas operations in the sea for as water depth increases so the oxygen content decreases • Dry corrosion: Metal come in contact with gases such as SO2, O2 Attack on steel by furnace gaseous

  10. Forms of corrosion1.Uniform Corrosion Rusting of iron roof Rusting of steel pipes

  11. Noble, cathodic end PlatinumGoldGraphiteTitaniumSilverHastelloy C18-8 austenitic stainless steels (passive condition)Iron-chromium alloys (passive condition)Inconel (passive)NickelMonelCupronickel alloysBronzesCopperBrassesInconel (active)Nickel (active)TinLead18-8 Austenitic stainless steels (active)13% Chromium stainless steel (active)Cast ironMild steel and ironCadmiumAluminum alloysZincMagnesium and magnesium alloys Active, anodic end GALVANIC SERIES

  12. Table.1 Change in weight of coupled and uncoupled steel and zinc, g

  13. Galvanic corrosion Large cathode area, small anode area showing relatively pronounced attack of the rivet head Large anode area, small cathode area showing relatively insignificant attack over a wide area of sheet.

  14. Prevention

  15. Galvanic corrosion in the Statue of Liberty Statue of Liberty

  16. CREVICE CORROSION • Intensive localized corrosion within crevices & shielded areas on metal surfaces • Small volumes of stagnant corrosive caused by holes, gaskets, surface deposits, lap joints CORROSION IN FLANG

  17. Mechansium of crevice

  18. crevice corrosion in a bolt and washer Rust stains can be seen in the roots of the threads

  19. PITTING CORROSION • Pitting corrosion is a localized form of corrosive attack that produces holes or small pits in a metal.

  20. Sewer Explosion due to Pitting Corrosion An example of corrosion damages with shared responsibilities was the sewer explosion that killed 215 people in Guadalajara, Mexico, in April 1992. Besides the fatalities, the series of blasts damaged 1,600 buildings and injured 1,500 people. Corrosion Pits are the primary source of leaks in water handling systems

  21. Corrosion Pit Shapes SIDEWAY PITS THROUGH PITS Subsurface Narrow, deep Shallow, wide Undercutting Elliptical Horizontal grain attack Vertical Grain Attack

  22. EROSION CORROSION Relative movement between corrosive fluid and the metal surface Erosion corrosion of condenser tube wall Erosion corrosion of stainless alloy pump impeller

  23. Cavitations corrosion •  Formation and collaps of vapur bubbles in a liquid state near metal surface • Control valves, pumps, propellers and impellers.

  24. Intergranular Corrosion

  25. FIG. Intergranular corrosion of a failed aircraft component made of 7075-T6 aluminum (picture width = 500 mm)  Fig. Severe problem in the welding of stainless steels, when it is termed weld decay.

  26. 18-8 SS

  27. Stress corrosion cracking Simultaneous presence of tensile stress and specific corrosive environment The collapsed Silver Bridge, as seen from the Ohio side

  28. Corrosion Measurement WEIGHT LOSS METHOD 534 W mpy= DAT W= weight loss, mg D= density of specimen, g/cm2 A= area of specimen, sq.in T= exposure time, hr

  29. Involve the use of a potentiostat for applying a potential (relative to a reference electrode) and measuring the current (flowing from the working electrode to the counter or auxiliary electrode) Corrosion Measurements

  30. Corrosion potential Corrosion current density

  31. Metal corrodes depends not only upon its electrode potential but also upon pH of the aqueous solution Figure 2: Pourbaix Diagram for Iron [1]. • Use of Inhibitors ( from point A to c ) • Anodic control ( from point A to b ) • Cathodic control( from point A to a )

  32. Corrosion prevention methods Material selection Metal and alloys

  33. Inhibitors • Added in small concentration to environment decreases the corrosion rate • Retarding catalyst • 1.Absorption- type inhibitors: • Organic compound which absorbs on metal surface and suppress metal dissolution and reduction reaction • e.g-amine • 2. Hydrogen evolution poisons: • Arsenic and antimony • Acid solution

  34. 3. Oxidizer: • Chromate, nitrate, and ferric salts • e.g- iron and its alloys and SS • 4. Scavengers • Removing corrosion reagents from solution • Sodium sulphate and hydrazine Inhibitive coating on steel surface

  35. DESIGN WALL THICKNESS: Wall thickness= 2* thickness • Design rules: • Weld rather than rivet tank • Design tanks and other containers for easy draining and easy cleaning • Avoid excessive stresses and stress conc. • Avoid electric contact between dissimilar metal

  36. Design

  37. Design Design tanks for easy drainage

  38. Cathodic protection 1824 HUMEPHERY DEVY USED CATHODIC PROTECTION ON BRTISH NAVEL SHIPS THE PRINCIPAL OF CATHODI C PROTECCTION: M = M n+ + ne- 2H+ + 2e- = H2 TWO METHODS OF CATHODIC PROTECTION 1. IMPRESSED CURRENT METHOD 2. USE OF SACRIFICAL ANODE

  39. Impressed current Cathodic protection of an underground tank using impressed current

  40. Galvanic coupling Protection of underground pipeline with magnesium rod Cathodic protection of Domestic hot-water tank using sacrificial anode

  41. Application • Protection of hull of a ship • Domestic and industrial water heater • Elevated water storage tank • Underground pipes • Boilers

  42. Anodic protection • Formation of protective of protective film on metals by externally applied anodic current • Metal to be protected made more anodic

  43. Anodic protection of stainless steel

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