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Why Study Corrosion 1

Why Study Corrosion 1 . Sheldon W. Dean 12/7/02. What is Corrosion?. What does it look like? How do you know when you have it?. What is Corrosion?. Metals made by smelting ( reduction of ore) Metals in air want to return to their oxidized state Corrosion is a natural process!.

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Why Study Corrosion 1

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  1. Why Study Corrosion 1 Sheldon W. Dean 12/7/02

  2. What is Corrosion? What does it look like? How do you know when you have it?

  3. What is Corrosion? • Metals made by smelting ( reduction of ore) • Metals in air want to return to their oxidized state • Corrosion is a natural process!

  4. Is Corrosion Important? • National issue? • International issue? • What industries are affected? • Does it affect us personally?

  5. Importance to USA • CC Technologies study – March 2002 • In 2000 about 3.1% of GDP spent on corrosion repair and control • Total cost $276Billion! • Of industries analyzed, the cost was $137.9 Billion

  6. Examples of Corrosion Damage • Automotive problems - body rust • Home examples- - Plumbing fixtures - Mail box - Exterior fixtures and fasteners • Concrete cracking

  7. Corrosion Affects Our Safety! • Unexpected failures of equipment and devices • Need to replace damaged items • Corrosion weakens structures - Need to evaluate fitness for service when corrosion occurs

  8. What Does Corrosion Look Like? • Rust and tarnish, red blue or gray scale • 8 types of damage – Fontana • Several others also.

  9. Most Common Forms of Corrosion • General attack (uniform wastage) • Pitting/ Crevice attack • Cracking (embrittlement) • Galvanic corrosion

  10. Corrosion is Electrochemical • Two different reactions occur - oxidation and reduction • Electron transfer occurs • Potential (voltage) driving force required • Oxidation occurs at anode • Reduction occurs at cathode

  11. Corrosion Reactions • Oxidation - e.g. Fe  Fe++ + 2e • Reduction – e.g. O2 + 2H2O  4OH- - 4e • Secondary - e.g. 4 Fe++ + O2  Fe2O3 + 8H+

  12. Conclusions • Corrosion rate depends upon the corrosion products that form • Solubility of corrosion products determines the rate • If solubility is high, the rate is high! • If solubility is low, the rate is low

  13. Potential/pH (Pourbaix) Diagram • Very useful way to present data • Developed by Marcel Pourbaix (1966) • Available for all metals and many other elements • Shows solubility and potential effects • If solubility is < 10-6 M/l, no corrosion is assumed

  14. Characteristics of Corrosion Products • Very thin and dense: protective,e.g., Cr, Al, Ti, 10 to 100 nm thick • Thin: protective but some corrosion occurs, e.g.,Cu, Zn, Pb 1 to 10 m • Thick and porous, e.g., Fe, >100 m Corrosion is a problem. • Soluble, e.g., Na, K Not able to be used.

  15. Dealing with Corrosion There are many ways to prevent or minimize corrosion damage

  16. Alloying to Resist Corrosion - Steel • Add >13% Cr (stainless steel) • Add >2% Mo to stainless (to resist pitting) • Add Si, P, Cu, Cr ( and others) to obtain weathering steel

  17. Alloying to Resist Corrosion - Copper • Add Ni and Fe (cupronickel) sea water • Add As, Sb, or P to prevent dealloying of brass (Cu + 10 to 35% Zn) • Add Al or Si to resist erosion

  18. Metallic Coatings • Widely used to protect steel and to make other metals more attractive • Zn and Zn alloys on steel – Galvanizing • Ni + Cr on steel, brass or zinc to give a bright finish • Cu + Ni + Cr also used for bright finish

  19. Organic Coatings - Paint • Barrier layer to keep water away • Adhesion is key to success • Susceptible to thermal damage • Susceptible to UV damage

  20. Electrochemical Protection • Cathodic protection – reduce the potential and also corrosion rate - widely used underground and in sea water • Anodic protection – increase potential to produce a less soluble corrosion product – used in some chemical plants

  21. Corrosion Inhibitors • Used in water systems: - Automotive cooling systems - Cooling towers - Boilers, especially high pressure steam • Temporary preservatives for metals - Volatile corrosion inhibitors • Paints and primers

  22. Quiz Time! • What is the most corrosive substance we can think of? • Corrosion damage only causes metals to become thinner – True or False? • How does corrosion affect me?

  23. Answers! • Water!!! • False! Corrosion also causes cracking, pitting, staining, wedging in crevices, loss of electrical conductivity, and failure of components • What is your answer?

  24. Break Time

  25. Why Study Corrosion - 2 Sheldon Dean 12/7/02

  26. Careers in CorrosionTechnician - Education • High school diploma + interest in chemistry or technology • Associates degree – possible night school - not required at entry level - Chemistry - Electrical technology - Materials science

  27. Careers in CorrosionTechnician-Work • Lab technician - Chemistry laboratory - Materials laboratory - Materials or chemical company • Field technician – civil engineering - Pipeline monitoring - Bridges, tunnels etc.

  28. Careers in CorrosionCivil Engineer - Education • Civil, mechanical or electrical SB • MBA or MS (not required but often helpful) • PE license • NACE Certification

  29. Careers in CorrosionCivil Engineer - Work • Engineering firm or consultant - Cathodic protection design - System monitoring and evaluation • State or local government - Specify protection systems for bridges, tunnels, other facilities - Inspection and monitoring

  30. Mat., Chem., Chem. Eng.Education • High School Diploma • College SB, Major: Mat. Eng., Chem., Chem. Eng., or Mech.Eng. • Grad school optional, MBA, MS or PhD • Certification NACE (optional) • PE License (optional)

  31. Mat.,Chem.,Chem. Eng.Work • Chemical, materials, petroleum, auto firm - Engineering - Safety - Research (PhD) - Plant Maintenance • Engineering or consultant firm

  32. NACE International • Short courses, some with certification • Annual meeting and show • Standards development • Local sections • Symposia • Books, videos and computer products

  33. NACE InternationalThe Corrosion Society • Address: P.O.Box218340, Houston,TX77218-8340 • Phone: 281-228-6200 • Website: www.nace.org

  34. ASTM International • Standards development, Vol.03.02 • Training courses • Symposia • Address:100 Barr Harbor Drive, West Conshocken, PA 19428-2959 • Website: www.astm.org • Corrosion committee: G-1

  35. Corrosion Testing • Used for a variety of purposes • Standard test methods available • Some tests are simple and easy to run • ASTM corrosion tests are in Volume 03.02 of the “Annual Book of ASTM Standards”

  36. Corrosion Testing-Purposes • Accelerated tests to demonstrate products durability • Acceptance tests to show that a material meets standard • Monitoring tests to show changes in a system corrosivity • Research tests to determine mechanism of corrosion

  37. Standard Tests • Usually corrosion tests have many parameters • Corrosion tests often give results that are difficult to reproduce – Standardization helps reproducibility • Consensus standard tests: ASTM and NACE

  38. Accelerated Test Example • ASTM G48 Pitting and Crevice Corrosion Resistance • Ferric chloride, 6%solution • 72Hrs at 22oC (room temperature) • Report pitting or crevice corrosion • Simulates sea water attack of stainless steels

  39. Acceptance Test - Al Alloys • ASTM G 69, Test of metallurgical condition of Al alloys • Measure potential,E, in salt solution • Cu increases E, Zn reduces E • Heat treatment determines condition • Condition affects strength and corrosion tendencies

  40. ASTM G 69 Continued • Solution: 1M Na Cl + 2.7%H2O2, 22oC • Surface preparation: 00 steel wool rub • 1 Hour immersion • Measure potential every 5 minutes after 30 minutes against SCE electrode • Average result: -750+/-10mV for pure Al • Al foil is pure Al

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